Some examples for the STM32F4-Disco board

examples/stm32/f4/stm32f4-disco/blink/Makefile

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+#
+# This file is part of the libopencm3 project.
+#
+# This library is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this library.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+BINARY = blink
+
+LDSCRIPT = ../stm32f4-disco.ld
+
+include ../../Makefile.include

examples/stm32/f4/stm32f4-disco/blink/README

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+README
+------
+
+The "HelloWorld" of embedded systems. This code is really really simple,
+it sets up the system clock at a known frequency (168Mhz) and enables
+a GPIO pin as an output, that happens to be connected to an LED. And it
+blinks it on and off.
+

examples/stm32/f4/stm32f4-disco/blink/blink.c

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+/* 
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2014 Chuck McManis (cmcmanis@mcmanis.com)
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <libopencm3/stm32/f4/rcc.h>
+#include <libopencm3/stm32/f4/gpio.h>
+
+#define GREEN_LED	GPIO13
+#define RED_LED		GPIO13
+
+int main(void)
+{
+	int i;
+
+	/* Use parameters to set the STM32 clock to 168 MHz. */
+	rcc_clock_setup_hse_3v3(&hse_8mhz_3v3[CLOCK_3V3_168MHZ]);
+
+	/* Enable GPIOG clock. (this enables the pins to work) */
+	rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPGEN);
+
+	/* Set the "mode" of the GPIO pin to output, no pullups or pulldowns */
+	gpio_mode_setup(GPIOG, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GREEN_LED );
+
+	/* Turn on the GREEN led */
+	gpio_set(GPIOG, GREEN_LED);
+
+	/* Blink the GREEN LED on the board. */
+	while (1) {
+		/* Toggle LEDs. */
+		gpio_toggle(GPIOG, GREEN_LED);
+		for (i = 0; i < 10000000; i++) /* Wait a bit. */
+			__asm__("nop");
+	}
+
+	return 0;
+}

examples/stm32/f4/stm32f4-disco/sdram/Makefile

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+#
+# This file is part of the libopencm3 project.
+#
+# This library is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this library.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+OBJS = console.o clock.o
+
+BINARY = sdram
+
+LDSCRIPT = ../stm32f4-disco.ld
+
+include ../../Makefile.include
+

examples/stm32/f4/stm32f4-disco/sdram/clock.c

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+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2013 Chuck McManis <cmcmanis@mcmanis.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * Now this is just the clock setup code from systick-blink as it is the
+ * transferrable part.
+ */
+
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/cm3/nvic.h>
+#include <libopencm3/cm3/systick.h>
+
+/* Common function descriptions */
+#include "clock.h"
+
+/* milliseconds since boot */
+static volatile uint32_t system_millis;
+
+/* Called when systick fires */
+void sys_tick_handler(void) {
+	system_millis++;
+}
+
+/* simple sleep for delay milliseconds */
+void msleep(uint32_t delay) {
+	uint32_t wake = system_millis + delay;
+	while (wake > system_millis) ;
+}
+
+/* Getter function for the current time */
+uint32_t mtime(void) {
+	return system_millis;
+}
+
+/*
+ * clock_setup(void)
+ *
+ * This function sets up both the base board clock rate
+ * and a 1khz "system tick" count. The SYSTICK counter is
+ * a standard feature of the Cortex-M series.
+ */
+void clock_setup(void)
+{
+	/* Base board frequency, set to 168Mhz */
+	rcc_clock_setup_hse_3v3(&hse_8mhz_3v3[CLOCK_3V3_168MHZ]);
+
+	/* clock rate / 168000 to get 1mS interrupt rate */
+	systick_set_reload(168000);
+	systick_set_clocksource(STK_CSR_CLKSOURCE_AHB);
+	systick_counter_enable();
+
+	/* this done last */
+	systick_interrupt_enable();
+}

examples/stm32/f4/stm32f4-disco/sdram/clock.h

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+/*
+ * This include file describes the functions exported by clock.c
+ */
+#ifndef __CLOCK_H
+#define __CLOCK_H
+
+/*
+ * Definitions for functions being abstracted out
+ */
+void msleep(uint32_t);
+uint32_t mtime(void);
+void clock_setup(void);
+
+#endif /* generic header protector */
+

examples/stm32/f4/stm32f4-disco/sdram/console.c

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+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2013 Chuck McManis <cmcmanis@mcmanis.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * USART example (alternate console)
+ *
+ * This version then adds in interrupts, which is really handy for
+ * the receive function as it is impossible to predict when someone
+ * might type a character, further you can create a "character based
+ * reset" capability if you choose to.
+ */
+
+#include <stdint.h>
+#include <setjmp.h>
+#include <libopencm3/stm32/gpio.h>
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/usart.h>
+#include <libopencm3/cm3/nvic.h>
+#include <libopencm3/stm32/iwdg.h>
+#include <libopencm3/cm3/scb.h>
+#include <libopencm3/cm3/cortex.h>
+#include "console.h"
+
+
+/*
+ * Some definitions of our console "functions" attached to the 
+ * USART.
+ *
+ * These define sort of the minimum "library" of functions which
+ * we can use on a serial port.
+ */
+
+
+#define CONSOLE_UART	USART2
+
+
+/* This is a ring buffer to holding characters as they are typed
+ * it maintains both the place to put the next character received
+ * from the UART, and the place where the last character was
+ * read by the program. See the README file for a discussion of
+ * the failure semantics.
+ */
+#define RECV_BUF_SIZE	128		// Arbitrary buffer size
+char recv_buf[RECV_BUF_SIZE];
+volatile int recv_ndx_nxt;		// Next place to store
+volatile int recv_ndx_cur;		// Next place to read
+
+/* For interrupt handling we add a new function which is called
+ * when recieve interrupts happen. The name (usart2_isr) is created
+ * by the irq.json file in libopencm3 calling this interrupt for
+ * USART2 'usart2', adding the suffix '_isr', and then weakly binding
+ * it to the 'do nothing' interrupt function in vec.c.
+ *
+ * By defining it in this file the linker will override that weak
+ * binding and instead bind it here, but you have to get the name
+ * right or it won't work. And you'll wonder where your interrupts
+ * are going.
+ */
+void usart2_isr(void) {
+	uint32_t	reg;
+	int			i;
+
+	do {
+		reg = USART_SR(CONSOLE_UART);
+		if (reg & USART_SR_RXNE) {
+			recv_buf[recv_ndx_nxt] = USART_DR(CONSOLE_UART);
+#ifdef RESET_ON_CTRLC
+			/* Check for "reset" */
+			if (recv_buf[recv_ndx_nxt] == '\003') {
+				/* reset the system */
+				volatile uint32_t *ret = (&reg) + 7;	// Return address on stack
+				
+				*ret = (uint32_t) &reset_handler;		// force system reset
+				return;									// go to new address
+			}
+#endif
+			/* Check for "overrun" */
+			i = (recv_ndx_nxt + 1) % RECV_BUF_SIZE;
+			if (i != recv_ndx_cur) {
+				recv_ndx_nxt = i;
+			}
+		}
+	} while ((reg & USART_SR_RXNE) != 0); // can read back-to-back interrupts
+}
+
+/*
+ * console_putc(char c)
+ *
+ * Send the character 'c' to the USART, wait for the USART
+ * transmit buffer to be empty first.
+ */
+void console_putc(char c) {
+	uint32_t	reg;
+	do {
+		reg = USART_SR(CONSOLE_UART);
+	} while ((reg & USART_SR_TXE) == 0);
+	USART_DR(CONSOLE_UART) = (uint16_t) c & 0xff;
+}
+
+/*
+ * char = console_getc(int wait)
+ *
+ * Check the console for a character. If the wait flag is
+ * non-zero. Continue checking until a character is received
+ * otherwise return 0 if called and no character was available.
+ *
+ * The implementation is a bit different however, now it looks
+ * in the ring buffer to see if a character has arrived.
+ */
+char console_getc(int wait) {
+	char		c = 0;
+
+	while ((wait != 0) && (recv_ndx_cur == recv_ndx_nxt)) ;
+	if (recv_ndx_cur != recv_ndx_nxt) {
+		c = recv_buf[recv_ndx_cur];
+		recv_ndx_cur = (recv_ndx_cur + 1) % RECV_BUF_SIZE;
+	}
+	return c;
+}
+
+/*
+ * void console_puts(char *s)
+ *
+ * Send a string to the console, one character at a time, return
+ * after the last character, as indicated by a NUL character, is
+ * reached.
+ */
+void console_puts(char *s) {
+	while (*s != '\000') {
+		console_putc(*s);
+		/* Add in a carraige return, after sending line feed */
+		if (*s == '\n') {
+			console_putc('\r');
+		}
+		s++;
+	}
+}
+
+/*
+ * int console_gets(char *s, int len)
+ *
+ * Wait for a string to be entered on the console, limited
+ * support for editing characters (back space and delete)
+ * end when a <CR> character is received.
+ */
+int console_gets(char *s, int len) {
+	char *t = s;
+	char c;
+
+	*t = '\000';
+	/* read until a <CR> is received */
+	while ((c = console_getc(1)) != '\r') {
+		if ((c == '\010') || (c == '\127')) {
+			if (t > s) {
+				/* send ^H ^H to erase previous character */
+				console_puts("\010 \010");
+				t--;
+			}
+		} else {
+			*t = c;
+			console_putc(c);
+			if ((t - s) < len) {
+				t++;
+			}
+		}
+		/* update end of string with NUL */
+		*t = '\000';
+	}
+	return (t - s);
+}
+
+/*
+ * Set up the GPIO subsystem with an "Alternate Function"
+ * on some of the pins, in this case connected to a
+ * USART.
+ */
+void console_setup(void) {
+
+	/* MUST enable the GPIO clock in ADDITION to the USART clock */
+	rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPDEN);
+
+	/* This example uses PD5 and PD6 for Tx and Rx respectively
+	 * but other pins are available for this role on USART2 (our chosen
+ 	 * USART) as well, such as PA2 and PA3. You can also split them
+	 * so PA2 for Tx, PD6 for Rx but you would have to enable both
+	 * the GPIOA and GPIOD clocks in that case
+	 */
+	gpio_mode_setup(GPIOD, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO5 | GPIO6);
+
+	/* Actual Alternate function number (in this case 7) is part
+	 * depenedent, check the data sheet for the right number to
+	 * use.
+	 */
+	gpio_set_af(GPIOD, GPIO_AF7, GPIO5 | GPIO6);
+
+
+	/* This then enables the clock to the USART2 peripheral which is
+	 * attached inside the chip to the APB2 bus. Different peripherals
+	 * attach to different buses, and even some UARTS are attached to
+	 * APB1 and some to APB2, again the data sheet is useful here.
+	 */
+	rcc_peripheral_enable_clock(&RCC_APB1ENR, RCC_APB1ENR_USART2EN);
+
+	/* Set up USART/UART parameters using the libopencm3 helper functions */
+	usart_set_baudrate(CONSOLE_UART, 115200);
+	usart_set_databits(CONSOLE_UART, 8);
+	usart_set_stopbits(CONSOLE_UART, USART_STOPBITS_1);
+	usart_set_mode(CONSOLE_UART, USART_MODE_TX_RX);
+	usart_set_parity(CONSOLE_UART, USART_PARITY_NONE);
+	usart_set_flow_control(CONSOLE_UART, USART_FLOWCONTROL_NONE);
+	usart_enable(CONSOLE_UART);
+
+	/* Enable interrupts from the USART */
+	nvic_enable_irq(NVIC_USART2_IRQ);
+
+	/* Specifically enable recieve interrupts */
+	usart_enable_rx_interrupt(CONSOLE_UART);
+}

examples/stm32/f4/stm32f4-disco/sdram/console.h

@@ -0,0 +1,13 @@
+/*
+ * Our simple console definitions
+ */
+
+void console_putc(char c);
+char console_getc(int wait);
+void console_puts(char *s);
+int console_gets(char *s, int len);
+void console_setup(void);
+
+/* this is for fun, if you type ^C to this example it will reset */
+#define RESET_ON_CTRLC
+

examples/stm32/f4/stm32f4-disco/sdram/sdram.c

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+/*
+ * sdram.c - SDRAM controller example
+ *
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2013 Chuck McManis <cmcmanis@mcmanis.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <libopencm3/stm32/gpio.h>
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/fsmc.h>
+#include "clock.h"
+#include "console.h"
+
+#define SDRAM_BASE_ADDRESS ((uint8_t *)(0xd0000000))
+
+void sdram_init(void);
+
+#ifndef NULL
+#define NULL	(void *)(0)
+#endif
+
+/*
+ * This is just syntactic sugar but it helps, all of these
+ * GPIO pins get configured in exactly the same way.
+ */
+static struct {
+	uint32_t	gpio;
+	uint16_t	pins;
+} sdram_pins[6] = {
+	{GPIOB, GPIO5 | GPIO6 },
+	{GPIOC, GPIO0 },
+	{GPIOD, GPIO0 | GPIO1 | GPIO8 | GPIO9 | GPIO10 | GPIO14 | GPIO15},
+	{GPIOE, GPIO0 | GPIO1 | GPIO7 | GPIO8 | GPIO9 | GPIO10 |
+			GPIO11 | GPIO12 | GPIO13 | GPIO14 | GPIO15 },
+	{GPIOF, GPIO0 | GPIO1 | GPIO2 | GPIO3 | GPIO4 | GPIO5 | GPIO11 |
+			GPIO12 | GPIO13 | GPIO14 | GPIO15 },
+	{GPIOG, GPIO0 | GPIO1 | GPIO4 | GPIO5 |GPIO8 | GPIO15}
+};
+
+static struct sdram_timing timing = {
+	.trcd = 2,		/* RCD Delay */
+	.trp = 2,		/* RP Delay */
+	.twr = 2,		/* Write Recovery Time */
+	.trc = 7,		/* Row Cycle Delay */
+	.tras = 4,		/* Self Refresh Time */
+	.txsr = 7,		/* Exit Self Refresh Time */
+	.tmrd = 2,		/* Load to Active Delay */
+};
+
+/*
+ * Initialize the SD RAM controller.
+ */
+void
+sdram_init(void) {
+	int i;
+	uint32_t cr_tmp, tr_tmp; // control, timing registers
+
+	/*
+	* First all the GPIO pins that end up as SDRAM pins
+	*/
+	rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPBEN);
+	rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPCEN);
+	rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPDEN);
+	rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPEEN);
+	rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPFEN);
+	rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPGEN);
+
+	for (i = 0; i < 6; i++) {
+		gpio_mode_setup(sdram_pins[i].gpio, GPIO_MODE_AF, GPIO_PUPD_NONE,
+						sdram_pins[i].pins);
+		gpio_set_output_options(sdram_pins[i].gpio, GPIO_OTYPE_PP,
+						GPIO_OSPEED_50MHZ, sdram_pins[i].pins);
+		gpio_set_af(sdram_pins[i].gpio, GPIO_AF12, sdram_pins[i].pins);
+	}
+
+	/* Enable the SDRAM Controller */
+	rcc_peripheral_enable_clock(&RCC_AHB3ENR, RCC_AHB3ENR_FMCEN);
+
+	/* Note the STM32F429-DISCO board has the ram attached to bank 2 */
+	/* Timing parameters computed for a 168Mhz clock */
+	/* These parameters are specific to the SDRAM chip on the board */
+
+	cr_tmp  = FMC_SDCR_RPIPE_1CLK;
+	cr_tmp |= FMC_SDCR_SDCLK_2HCLK;
+	cr_tmp |= FMC_SDCR_CAS_3CYC;
+	cr_tmp |= FMC_SDCR_NB4;
+	cr_tmp |= FMC_SDCR_MWID_16b;
+	cr_tmp |= FMC_SDCR_NR_12;
+	cr_tmp |= FMC_SDCR_NC_8;
+
+	/* We're programming BANK 2, but per the manual some of the parameters
+	 * only work in CR1 and TR1 so we pull those off and put them in the
+	 * right place.
+	 */
+	FMC_SDCR1 |= (cr_tmp & FMC_SDCR_DNC_MASK);
+	FMC_SDCR2 = cr_tmp;
+	
+	tr_tmp = sdram_timing(&timing);
+	FMC_SDTR1 |= (tr_tmp & FMC_SDTR_DNC_MASK);
+	FMC_SDTR2 = tr_tmp;
+
+	/* Now start up the Controller per the manual
+	 *	- Clock config enable
+	 *	- PALL state
+	 *	- set auto refresh
+	 *	- Load the Mode Register
+	 */
+	sdram_command(SDRAM_BANK2, SDRAM_CLK_CONF, 1, 0);
+	msleep(1); // sleep at least 100uS
+	sdram_command(SDRAM_BANK2, SDRAM_PALL, 1, 0);
+	sdram_command(SDRAM_BANK2, SDRAM_AUTO_REFRESH, 4, 0);
+	tr_tmp = SDRAM_MODE_BURST_LENGTH_2				|
+				SDRAM_MODE_BURST_TYPE_SEQUENTIAL	|
+				SDRAM_MODE_CAS_LATENCY_3			|
+				SDRAM_MODE_OPERATING_MODE_STANDARD	|
+				SDRAM_MODE_WRITEBURST_MODE_SINGLE;
+	sdram_command(SDRAM_BANK2, SDRAM_LOAD_MODE, 1, tr_tmp);
+
+	/*
+	 * set the refresh counter to insure we kick off an
+	 * auto refresh often enough to prevent data loss.
+	 */
+	FMC_SDRTR = 683;
+	/* and Poof! a 8 megabytes of ram shows up in the address space */
+}
+
+/*
+ * This code are some routines that implement a "classic"
+ * hex dump style memory dump. So you can look at what is
+ * in the RAM, alter it (in a couple of automated ways)
+ */
+void dump_byte(uint8_t b);
+void dump_long(uint32_t l);
+uint8_t *dump_line(uint8_t *, uint8_t *);
+uint8_t *dump_page(uint8_t *, uint8_t *);
+
+
+/* make a nybble into an ascii hex character 0 - 9, A-F */
+#define HEX_CHAR(x)	((((x) + '0') > '9') ? ((x) + '7') : ((x) + '0'))
+
+/* send an 8 bit byte as two HEX characters to the console */
+void dump_byte(uint8_t b) {
+	console_putc(HEX_CHAR((b >> 4) & 0xf));
+	console_putc(HEX_CHAR(b & 0xf));
+}
+
+/* send a 32 bit value as 8 hex characters to the console */
+void dump_long(uint32_t l) {
+	int i = 0;
+	for (i = 0; i < 8; i++) {
+		console_putc(HEX_CHAR((l >> (28 - i * 4)) & 0xf));
+	}
+}
+
+/*
+ * dump a 'line' (an address, 16 bytes, and then the
+ * ASCII representation of those bytes) to the console.
+ * Takes an address (and possiblye a 'base' parameter
+ * so that you can offset the address) and sends 16
+ * bytes out. Returns the address +16 so you can
+ * just call it repeatedly and it will send the
+ * next 16 bytes out.
+ */
+uint8_t *
+dump_line(uint8_t *addr, uint8_t *base) {
+	uint8_t *line_addr;
+	uint8_t b;
+	uint32_t tmp;
+	int i;
+
+	line_addr = addr;
+	tmp = (uint32_t)line_addr - (uint32_t) base;
+	dump_long(tmp);
+	console_puts(" | ");
+	for (i = 0; i < 16; i++) {
+		dump_byte(*(line_addr+i));
+		console_putc(' ');
+		if (i == 7) {
+			console_puts("  ");
+		}
+	}
+	console_puts("| ");
+	for (i = 0; i < 16; i++) {
+		b = *line_addr++;
+		console_putc(((b > 126) || (b < 32)) ? '.' : (char) b);
+	}
+	console_puts("\n");
+	return line_addr;
+}
+
+
+/*
+ * dump a 'page' like the function dump_line except this
+ * does 16 lines for a total of 256 bytes. Back in the
+ * day when you had a 24 x 80 terminal this fit nicely
+ * on the screen with some other information.
+ */
+uint8_t *
+dump_page(uint8_t *addr, uint8_t *base) {
+	int i;
+	for (i = 0; i < 16; i++) {
+		addr = dump_line(addr, base);
+	}
+	return addr;
+}
+
+/*
+ * This example initializes the SDRAM controller and dumps
+ * it out to the console. You can do various things like
+ * (FI) fill with increment, (F0) fill with 0, (FF) fill
+ * with FF. NP (next page), PP (prev page), NL (next line),
+ * (PL) previous line, and (?) for help.
+ */
+int
+main(void) {
+	int i;
+	uint8_t *addr;
+	char	c;
+
+	clock_setup();
+	console_setup();
+	sdram_init();
+
+	console_puts("SDRAM Example.\n");
+	console_puts("Original data:\n");
+	addr = (uint8_t *)(0xd0000000);
+	(void) dump_page(addr, NULL);
+	addr = SDRAM_BASE_ADDRESS;
+	for (i = 0; i < 256; i++) {
+		*(addr + i) = i;
+	}
+	console_puts("Modified data (with Fill Increment)\n");
+	addr = SDRAM_BASE_ADDRESS;
+	addr = dump_page( addr, NULL);
+	while (1) {
+		console_puts("CMD> ");
+		switch (c = console_getc(1)) {
+			case 'f':
+			case 'F':
+				console_puts("Fill ");
+				switch (c = console_getc(1)) {
+					case 'i':
+					case 'I':
+						console_puts("Increment\n");
+						for (i = 0; i < 256; i++) {
+							*(addr+i) = i;
+						}
+						dump_page(addr, NULL);
+						break;
+					case '0':
+						console_puts("Zero\n");
+						for (i = 0; i < 256; i++) {
+							*(addr+i) = 0;
+						}
+						dump_page(addr, NULL);
+						break;
+					case 'f':
+					case 'F':
+						console_puts("Ones (0xff)\n");
+						for (i = 0; i < 256; i++) {
+							*(addr+i) = 0xff;
+						}
+						dump_page(addr, NULL);
+						break;
+					default:
+						console_puts("Unrecognized Command, press ? for help\n");
+				}
+				break;
+			case 'n':
+			case 'N':
+				console_puts("Next ");
+				switch (c = console_getc(1)) {
+					case 'p':
+					case 'P':
+						console_puts("Page\n");
+						addr += 256;
+						dump_page(addr, NULL);
+						break;
+					case 'l':
+					case 'L':
+						console_puts("Line\n");
+						addr += 16;
+						dump_line(addr, NULL);
+						break;
+					default:
+						console_puts("Unrecognized Command, press ? for help\n");
+				}
+				break;
+			case 'p':
+			case 'P':
+				console_puts("Previous ");
+				switch (c = console_getc(1)) {
+					case 'p':
+					case 'P':
+						console_puts("Page\n");
+						addr -= 256;
+						dump_page(addr, NULL);
+						break;
+					case 'l':
+					case 'L':
+						console_puts("Line\n");
+						addr -= 16;
+						dump_line(addr, NULL);
+						break;
+					default:
+						console_puts("Unrecognized Command, press ? for help\n");
+				}
+				break;
+			case '?':
+			default:
+				console_puts("Help\n");
+				console_puts(" n p - dump next page\n");
+				console_puts(" n l - dump next line\n");
+				console_puts(" p p - dump previous page\n");
+				console_puts(" p l - dump previous line\n");
+				console_puts(" f 0 - fill current page with 0\n");
+				console_puts(" f i - fill current page with 0 to 255\n");
+				console_puts(" f f - fill current page with 0xff\n");
+				console_puts(" ? - this message\n");
+				break;
+		}
+	}
+}

examples/stm32/f4/stm32f4-disco/stm32f4-disco.ld

@@ -0,0 +1,32 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2009 Uwe Hermann <uwe@hermann-uwe.de>
+ * Copyright (C) 2011 Stephen Caudle <scaudle@doceme.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/* Linker script for ST STM32F4DISCOVERY "DISCO" (STM32F429, 2024K flash, 192K RAM). */
+
+/* Define memory regions. */
+MEMORY
+{
+	rom (rx) : ORIGIN = 0x08000000, LENGTH = 2048K
+	ram (rwx) : ORIGIN = 0x20000000, LENGTH = 128K
+}
+
+/* Include the common ld script. */
+INCLUDE libopencm3_stm32f4.ld
+

examples/stm32/f4/stm32f4-disco/systick-blink/Makefile

@@ -0,0 +1,22 @@
+#
+# This file is part of the libopencm3 project.
+#
+# This library is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this library.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+BINARY = systick-blink
+
+LDSCRIPT = ../stm32f4-disco.ld
+
+include ../../Makefile.include

examples/stm32/f4/stm32f4-disco/systick-blink/README

@@ -0,0 +1,7 @@
+Systick Blink
+-------------
+
+This version of blink is slightly more sophisticated, it shows how you
+can initialize the Cortex M SYSTICK register to give a regular interrupt.
+It adds a function for doing precise delays. The original blink code
+is then rewritten with this in mind to create a 10Hz blinking pattern.

examples/stm32/f4/stm32f4-disco/systick-blink/systick-blink.c

@@ -0,0 +1,93 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2013 Chuck McManis <cmcmanis@mcmanis.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/* This version derived from fancy blink */
+
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/gpio.h>
+#include <libopencm3/cm3/nvic.h>
+#include <libopencm3/cm3/systick.h>
+
+/*
+ * Definitions for functions being abstracted out
+ */
+void msleep(uint32_t);
+void clock_setup(void);
+
+/* monotonically increasing number of milliseconds from reset
+ * overflows every 49 days if you're wondering
+ */
+volatile uint32_t system_millis;
+
+/* Called when systick fires */
+void sys_tick_handler(void) {
+	system_millis++;
+}
+
+/* sleep for delay milliseconds */
+void msleep(uint32_t delay) {
+	uint32_t wake = system_millis + delay;
+	while (wake > system_millis) ;
+}
+
+
+/*
+ * clock_setup(void)
+ *
+ * This function sets up both the base board clock rate
+ * and a 1khz "system tick" count. The SYSTICK counter is
+ * a standard feature of the Cortex-M series.
+ */
+void clock_setup(void)
+{
+	/* Base board frequency, set to 168Mhz */
+	rcc_clock_setup_hse_3v3(&hse_8mhz_3v3[CLOCK_3V3_168MHZ]);
+
+	/* clock rate / 168000 to get 1mS interrupt rate */
+	systick_set_reload(168000);
+	systick_set_clocksource(STK_CSR_CLKSOURCE_AHB);
+	systick_counter_enable();
+
+	/* this done last */
+	systick_interrupt_enable();
+}
+
+int main(void)
+{
+	/* Set up clock and systick */
+	clock_setup();
+
+	/* Enable GPIOD clock. */
+	rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPGEN);
+
+	/* Set GPIO13-14 (in GPIO port G) to 'output push-pull'. */
+	gpio_mode_setup(GPIOG, GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GPIO13 | GPIO14);
+
+	/* Set LED for alternating effect when toggling. */
+	gpio_set(GPIOG, GPIO13);
+
+	/* Blink the LEDs (PD12, PD13, PD14 and PD15) on the board. */
+	while (1) {
+		gpio_toggle(GPIOG, GPIO13 | GPIO14);
+		/* Now sleep for 100ms which toggles at 10hz rate */
+		msleep(100);
+	}
+
+	return 0;
+}

examples/stm32/f4/stm32f4-disco/usart-irq/Makefile

@@ -0,0 +1,28 @@
+#
+# This file is part of the libopencm3 project.
+#
+# This library is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this library.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+OBJS = clock.o
+
+BINARY = usart-irq
+
+# Example showing how to generate a map file.
+LDFLAGS += -Wl,--Map=$(BINARY).map
+
+LDSCRIPT = ../stm32f4-disco.ld
+
+include ../../Makefile.include
+

examples/stm32/f4/stm32f4-disco/usart-irq/README

@@ -0,0 +1,27 @@
+USART IRQ
+---------
+
+This is a slightly fancier console interface using interrupts. Basically
+this example sets up the USART for serial input and output as before
+except that the receive side is interrupt driven. That means you program
+won't miss a character if it happens to be taking its time printing something
+at the time.
+
+I've demonstrated this by setting it up so that if you type ^C to the
+program it causes an interrupt to occur that resets the program back
+to the start. This is done in a slightly tricky way to accomodate the
+Cortex M architecture. When you are interrupted in the Cortex M, the 
+proccessor goes into "Handler" mode, saves information on the stack,
+and takes the interrupt. Part of this involves saving a special value
+on the stack in the LR register. The useful thing is that it means you
+can write interrupt service routines as regular C code, the not so useful
+thing is that if you don't return from that stack, the processor gets
+confused about what state it should be in. So to avoid confusing the
+processor, the interrupt routine changes where the code will return, then
+does the return. This pops the processor out of Handler mode and back into
+Thread mode, at which point the C code can do a longjump.
+
+In the future, the C library may be able to note that the processor needs
+to change state for you, and save the special gymnastics here, but in the
+mean time this works and will continue to work in the future.
+

examples/stm32/f4/stm32f4-disco/usart-irq/clock.c

@@ -0,0 +1,70 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2013 Chuck McManis <cmcmanis@mcmanis.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * Now this is just the clock setup code from systick-blink as it is the
+ * transferrable part.
+ */
+
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/cm3/nvic.h>
+#include <libopencm3/cm3/systick.h>
+
+/* Common function descriptions */
+#include "clock.h"
+
+/* milliseconds since boot */
+static volatile uint32_t system_millis;
+
+/* Called when systick fires */
+void sys_tick_handler(void) {
+	system_millis++;
+}
+
+/* simple sleep for delay milliseconds */
+void msleep(uint32_t delay) {
+	uint32_t wake = system_millis + delay;
+	while (wake > system_millis) ;
+}
+
+/* Getter function for the current time */
+uint32_t mtime(void) {
+	return system_millis;
+}
+
+/*
+ * clock_setup(void)
+ *
+ * This function sets up both the base board clock rate
+ * and a 1khz "system tick" count. The SYSTICK counter is
+ * a standard feature of the Cortex-M series.
+ */
+void clock_setup(void)
+{
+	/* Base board frequency, set to 168Mhz */
+	rcc_clock_setup_hse_3v3(&hse_8mhz_3v3[CLOCK_3V3_168MHZ]);
+
+	/* clock rate / 168000 to get 1mS interrupt rate */
+	systick_set_reload(168000);
+	systick_set_clocksource(STK_CSR_CLKSOURCE_AHB);
+	systick_counter_enable();
+
+	/* this done last */
+	systick_interrupt_enable();
+}

examples/stm32/f4/stm32f4-disco/usart-irq/clock.h

@@ -0,0 +1,16 @@
+/* vim: set noexpandtab ts=4 :
+ *
+ * This include file describes the functions exported by clock.c
+ */
+#ifndef __CLOCK_H
+#define __CLOCK_H
+
+/*
+ * Definitions for functions being abstracted out
+ */
+void msleep(uint32_t);
+uint32_t mtime(void);
+void clock_setup(void);
+
+#endif /* generic header protector */
+

examples/stm32/f4/stm32f4-disco/usart-irq/usart-irq.c

@@ -0,0 +1,341 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2013 Chuck McManis <cmcmanis@mcmanis.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * USART interrupt driven example
+ *
+ * This version then adds in interrupts, which is really handy for
+ * the receive function as it is impossible to predict when someone
+ * might type a character, further you can create a "character based
+ * reset" capability if you choose to.
+ */
+
+#include <stdint.h>
+#include <setjmp.h>
+#include <libopencm3/stm32/gpio.h>
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/usart.h>
+#include <libopencm3/cm3/nvic.h>
+#include <libopencm3/stm32/iwdg.h>
+#include <libopencm3/cm3/scb.h>
+#include <libopencm3/cm3/cortex.h>
+#include "clock.h"
+
+
+/*
+ * Some definitions of our console "functions" attached to the
+ * USART.
+ *
+ * These define sort of the minimum "library" of functions which
+ * we can use on a serial port. If you wish to use a different
+ * USART there are several things to change:
+ * 	- CONSOLE_UART change this
+ *	- Change the peripheral enable clock
+ *	- add usartx_isr for interrupts
+ *	- nvic_enable_interrupt(your choice of USART/UART)
+ *	- GPIO pins for transmit/receive
+ *		(may be on different alternate functions as well)
+ */
+
+
+#define CONSOLE_UART	USART2
+
+void console_putc(char c);
+char console_getc(int wait);
+void console_puts(char *s);
+int console_gets(char *s, int len);
+
+/* this is for fun, if you type ^C to this example it will reset */
+#define RESET_ON_CTRLC
+
+#ifdef RESET_ON_CTRLC
+
+/* Jump buffer for setjmp/longjmp */
+jmp_buf	jump_buf;
+
+static void do_the_nasty(void);
+/*
+ * do_the_nasty
+ *
+ * This is a hack to implement the equivalent of a signal interrupt
+ * in a system without signals or a kernel or scheduler. Basically
+ * when the console_getc() function reads a '^C' character, it munges
+ * the return address of the interrupt to here, and then this function
+ * does a longjump to the last place we did a setjmp.
+ */
+static void do_the_nasty(void) {
+	longjmp(jump_buf, 1);
+	while(1) ;
+}
+#endif
+
+/* This is a ring buffer to holding characters as they are typed
+ * it maintains both the place to put the next character received
+ * from the UART, and the place where the last character was
+ * read by the program. See the README file for a discussion of
+ * the failure semantics.
+ */
+#define RECV_BUF_SIZE	128		// Arbitrary buffer size
+char recv_buf[RECV_BUF_SIZE];
+volatile int recv_ndx_nxt;		// Next place to store
+volatile int recv_ndx_cur;		// Next place to read
+
+/* For interrupt handling we add a new function which is called
+ * when recieve interrupts happen. The name (usart2_isr) is created
+ * by the irq.json file in libopencm3 calling this interrupt for
+ * USART2 'usart2', adding the suffix '_isr', and then weakly binding
+ * it to the 'do nothing' interrupt function in vec.c.
+ *
+ * By defining it in this file the linker will override that weak
+ * binding and instead bind it here, but you have to get the name
+ * right or it won't work. And you'll wonder where your interrupts
+ * are going.
+ */
+void usart2_isr(void) {
+	uint32_t	reg;
+	int			i;
+
+	do {
+		reg = USART_SR(CONSOLE_UART);
+		if (reg & USART_SR_RXNE) {
+			recv_buf[recv_ndx_nxt] = USART_DR(CONSOLE_UART);
+#ifdef RESET_ON_CTRLC
+			/* Check for "reset" */
+			if (recv_buf[recv_ndx_nxt] == '\003') {
+				/* reset the system
+				 * volatile definition of return address on the stack
+				 * to insure it gets stored, changed to point to
+				 * the trampoline function (do_the_nasty) which is
+				 * required because we need to return of an interrupt
+				 * to get the internal value of the LR register reset
+				 * and put the processor back into "Thread" mode from
+				 * "Handler" mode.
+				 *
+				 * See the PM0214 Programming Manual for Cortex M,
+				 * pg 42, to see the format of the Cortex M4 stack after
+				 * an interrupt or exception has occurred.
+				 */
+				volatile uint32_t *ret = (&reg) + 7;
+				
+				*ret = (uint32_t) &do_the_nasty;
+				return;
+			}
+#endif
+			/* Check for "overrun" */
+			i = (recv_ndx_nxt + 1) % RECV_BUF_SIZE;
+			if (i != recv_ndx_cur) {
+				recv_ndx_nxt = i;
+			}
+		}
+	} while ((reg & USART_SR_RXNE) != 0); // can read back-to-back interrupts
+}
+
+/*
+ * console_putc(char c)
+ *
+ * Send the character 'c' to the USART, wait for the USART
+ * transmit buffer to be empty first.
+ */
+void console_putc(char c) {
+	uint32_t	reg;
+	do {
+		reg = USART_SR(CONSOLE_UART);
+	} while ((reg & USART_SR_TXE) == 0);
+	USART_DR(CONSOLE_UART) = (uint16_t) c & 0xff;
+}
+
+/*
+ * char = console_getc(int wait)
+ *
+ * Check the console for a character. If the wait flag is
+ * non-zero. Continue checking until a character is received
+ * otherwise return 0 if called and no character was available.
+ *
+ * The implementation is a bit different however, now it looks
+ * in the ring buffer to see if a character has arrived.
+ */
+char console_getc(int wait) {
+	char		c = 0;
+
+	while ((wait != 0) && (recv_ndx_cur == recv_ndx_nxt)) ;
+	if (recv_ndx_cur != recv_ndx_nxt) {
+		c = recv_buf[recv_ndx_cur];
+		recv_ndx_cur = (recv_ndx_cur + 1) % RECV_BUF_SIZE;
+	}
+	return c;
+}
+
+/*
+ * void console_puts(char *s)
+ *
+ * Send a string to the console, one character at a time, return
+ * after the last character, as indicated by a NUL character, is
+ * reached.
+ */
+void console_puts(char *s) {
+	while (*s != '\000') {
+		console_putc(*s);
+		/* Add in a carraige return, after sending line feed */
+		if (*s == '\n') {
+			console_putc('\r');
+		}
+		s++;
+	}
+}
+
+/*
+ * int console_gets(char *s, int len)
+ *
+ * Wait for a string to be entered on the console, limited
+ * support for editing characters (back space and delete)
+ * end when a <CR> character is received.
+ */
+int console_gets(char *s, int len) {
+	char *t = s;
+	char c;
+
+	*t = '\000';
+	/* read until a <CR> is received */
+	while ((c = console_getc(1)) != '\r') {
+		if ((c == '\010') || (c == '\127')) {
+			if (t > s) {
+				/* send ^H ^H to erase previous character */
+				console_puts("\010 \010");
+				t--;
+			}
+		} else {
+			*t = c;
+			console_putc(c);
+			if ((t - s) < len) {
+				t++;
+			}
+		}
+		/* update end of string with NUL */
+		*t = '\000';
+	}
+	return (t - s);
+}
+
+void countdown(void);
+
+/*
+ * countdown
+ *
+ * Count down for 20 seconds to 0.
+ *
+ * This provides an example function which is constantly
+ * printing for 20 seconds and not looking for typed characters.
+ * however with the interrupt driven receieve queue you can type
+ * ^C while it is counting down and it will be interrupted. 
+ */
+void countdown(void) {
+	int i = 200;
+	while (i-- > 0) {
+		console_puts("Countdown: ");
+		console_putc( (i / 600) + '0');
+		console_putc(':');
+		console_putc( ((i % 600) / 100) + '0');
+		console_putc( (((i % 600) / 10) % 10) + '0');
+		console_putc('.');
+		console_putc( ((i % 600) % 10) + '0');
+		console_putc('\r');
+		msleep(100);
+	}
+}
+
+/*
+ * Set up the GPIO subsystem with an "Alternate Function"
+ * on some of the pins, in this case connected to a
+ * USART.
+ */
+int main(void) {
+	char buf[128];
+	int	len;
+	bool pmask;
+
+	clock_setup(); // initialize our clock
+
+	/* MUST enable the GPIO clock in ADDITION to the USART clock */
+	rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPDEN);
+
+	/* This example uses PD5 and PD6 for Tx and Rx respectively
+	 * but other pins are available for this role on USART2 (our chosen
+ 	 * USART) as well, such as PA2 and PA3. You can also split them
+	 * so PA2 for Tx, PD6 for Rx but you would have to enable both
+	 * the GPIOA and GPIOD clocks in that case
+	 */
+	gpio_mode_setup(GPIOD, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO5 | GPIO6);
+
+	/* Actual Alternate function number (in this case 7) is part
+	 * depenedent, CHECK THE DATA SHEET for the right number to
+	 * use.
+	 */
+	gpio_set_af(GPIOD, GPIO_AF7, GPIO5 | GPIO6);
+
+
+	/* This then enables the clock to the USART2 peripheral which is
+	 * attached inside the chip to the APB2 bus. Different peripherals
+	 * attach to different buses, and even some UARTS are attached to
+	 * APB1 and some to APB2, again the data sheet is useful here.
+	 */
+	rcc_peripheral_enable_clock(&RCC_APB1ENR, RCC_APB1ENR_USART2EN);
+
+	/* Set up USART/UART parameters using the libopencm3 helper functions */
+	usart_set_baudrate(CONSOLE_UART, 115200);
+	usart_set_databits(CONSOLE_UART, 8);
+	usart_set_stopbits(CONSOLE_UART, USART_STOPBITS_1);
+	usart_set_mode(CONSOLE_UART, USART_MODE_TX_RX);
+	usart_set_parity(CONSOLE_UART, USART_PARITY_NONE);
+	usart_set_flow_control(CONSOLE_UART, USART_FLOWCONTROL_NONE);
+	usart_enable(CONSOLE_UART);
+
+	/* Enable interrupts from the USART */
+	nvic_enable_irq(NVIC_USART2_IRQ);
+
+	/* Specifically enable recieve interrupts */
+	usart_enable_rx_interrupt(CONSOLE_UART);
+
+	/* At this point our console is ready to go so we can create our
+	 * simple application to run on it.
+	 */
+	console_puts("\nUART Demonstration Application\n");
+#ifdef RESET_ON_CTRLC
+	console_puts("Press ^C at any time to reset system.\n");
+	pmask = cm_mask_interrupts(0);
+	cm_mask_interrupts(pmask);
+	if (setjmp(jump_buf)) {
+		console_puts("\nInterrupt received! Restarting from the top\n");
+	}
+#endif
+	while (1) {
+		console_puts("Enter a string: ");
+		len = console_gets(buf, 128);
+		if (len) {
+			if (buf[0] == 'c') {
+				console_puts("\n");
+				countdown();	// long running thing (20 seconds)
+			}
+			console_puts("\nYou entered : '");
+			console_puts(buf);
+			console_puts("'\n");
+		} else {
+			console_puts("\nNo string entered\n");
+		}
+	}
+}

examples/stm32/f4/stm32f4-disco/usart/Makefile

@@ -0,0 +1,25 @@
+#
+# This file is part of the libopencm3 project.
+#
+# This library is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this library.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+OBJS = clock.o
+
+BINARY = usart
+
+LDSCRIPT = ../stm32f4-disco.ld
+
+include ../../Makefile.include
+

examples/stm32/f4/stm32f4-disco/usart/README

@@ -0,0 +1,9 @@
+Simple USART Example
+--------------------
+
+This example sets up a USART port and provides a few simple
+character handling functions to that a short interactive program
+can be demonstrated. It re-uses the clock setup from systick_blink
+and that means you could do times delays but that aspect isn't used.
+
+After this example we do character handling with interrupts.

examples/stm32/f4/stm32f4-disco/usart/clock.c

@@ -0,0 +1,71 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2013 Chuck McManis <cmcmanis@mcmanis.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * Now this is just the clock setup code from systick-blink as it is the
+ * transferrable part.
+ */
+
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/gpio.h>
+#include <libopencm3/cm3/nvic.h>
+#include <libopencm3/cm3/systick.h>
+
+/* Common function descriptions */
+#include "clock.h"
+
+/* milliseconds since boot */
+static volatile uint32_t system_millis;
+
+/* Called when systick fires */
+void sys_tick_handler(void) {
+	system_millis++;
+}
+
+/* simple sleep for delay milliseconds */
+void msleep(uint32_t delay) {
+	uint32_t wake = system_millis + delay;
+	while (wake > system_millis) ;
+}
+
+/* Getter function for the current time */
+uint32_t mtime(void) {
+	return system_millis;
+}
+
+/*
+ * clock_setup(void)
+ *
+ * This function sets up both the base board clock rate
+ * and a 1khz "system tick" count. The SYSTICK counter is
+ * a standard feature of the Cortex-M series.
+ */
+void clock_setup(void)
+{
+	/* Base board frequency, set to 168Mhz */
+	rcc_clock_setup_hse_3v3(&hse_8mhz_3v3[CLOCK_3V3_168MHZ]);
+
+	/* clock rate / 168000 to get 1mS interrupt rate */
+	systick_set_reload(168000);
+	systick_set_clocksource(STK_CSR_CLKSOURCE_AHB);
+	systick_counter_enable();
+
+	/* this done last */
+	systick_interrupt_enable();
+}

examples/stm32/f4/stm32f4-disco/usart/clock.h

@@ -0,0 +1,15 @@
+/*
+ * This include file describes the functions exported by clock.c
+ */
+#ifndef __CLOCK_H
+#define __CLOCK_H
+
+/*
+ * Definitions for functions being abstracted out
+ */
+void msleep(uint32_t);
+uint32_t mtime(void);
+void clock_setup(void);
+
+#endif /* generic header protector */
+

examples/stm32/f4/stm32f4-disco/usart/usart.c

@@ -0,0 +1,184 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2013 Chuck McManis <cmcmanis@mcmanis.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * USART example (alternate console)
+ */
+
+#include <stdint.h>
+#include <libopencm3/stm32/gpio.h>
+#include <libopencm3/stm32/rcc.h>
+#include <libopencm3/stm32/usart.h>
+#include "clock.h"
+
+/*
+ * Some definitions of our console "functions" attached to the
+ * USART.
+ *
+ * These define sort of the minimum "library" of functions which
+ * we can use on a serial port. 
+ */
+
+#define CONSOLE_UART	USART2
+
+void console_putc(char c);
+char console_getc(int wait);
+void console_puts(char *s);
+int console_gets(char *s, int len);
+
+/*
+ * console_putc(char c)
+ *
+ * Send the character 'c' to the USART, wait for the USART
+ * transmit buffer to be empty first.
+ */
+void console_putc(char c) {
+	uint32_t	reg;
+	do {
+		reg = USART_SR(CONSOLE_UART);
+	} while ((reg & USART_SR_TXE) == 0);
+	USART_DR(CONSOLE_UART) = (uint16_t) c & 0xff;
+}
+
+/*
+ * char = console_getc(int wait)
+ *
+ * Check the console for a character. If the wait flag is
+ * non-zero. Continue checking until a character is received
+ * otherwise return 0 if called and no character was available.
+ */
+char console_getc(int wait) {
+	uint32_t	reg;
+	do {
+		reg = USART_SR(CONSOLE_UART);
+	} while ((wait != 0) && ((reg & USART_SR_RXNE) == 0));
+	return (reg & USART_SR_RXNE) ? USART_DR(CONSOLE_UART) : '\000';
+}
+
+/*
+ * void console_puts(char *s)
+ *
+ * Send a string to the console, one character at a time, return
+ * after the last character, as indicated by a NUL character, is
+ * reached.
+ */
+void console_puts(char *s) {
+	while (*s != '\000') {
+		console_putc(*s);
+		/* Add in a carraige return, after sending line feed */
+		if (*s == '\n') {
+			console_putc('\r');
+		}
+		s++;
+	}
+}
+
+/*
+ * int console_gets(char *s, int len)
+ *
+ * Wait for a string to be entered on the console, limited
+ * support for editing characters (back space and delete)
+ * end when a <CR> character is received.
+ */
+int console_gets(char *s, int len) {
+	char *t = s;
+	char c;
+
+	*t = '\000';
+	/* read until a <CR> is received */
+	while ((c = console_getc(1)) != '\r') {
+		if ((c == '\010') || (c == '\127')) {
+			if (t > s) {
+				/* send ^H ^H to erase previous character */
+				console_puts("\010 \010");
+				t--;
+			}
+		} else {
+			*t = c;
+			console_putc(c);
+			if ((t - s) < len) {
+				t++;
+			}
+		}
+		/* update end of string with NUL */
+		*t = '\000';
+	}
+	return (t - s);
+}
+
+/*
+ * Set up the GPIO subsystem with an "Alternate Function"
+ * on some of the pins, in this case connected to a
+ * USART.
+ */
+int main(void) {
+	char buf[128];
+	int	len;
+
+	clock_setup(); // initialize our clock
+
+	/* MUST enable the GPIO clock in ADDITION to the USART clock */
+	rcc_peripheral_enable_clock(&RCC_AHB1ENR, RCC_AHB1ENR_IOPDEN);
+
+	/* This example uses PD5 and PD6 for Tx and Rx respectively
+     * but other pins are available for this role on USART2 (our chosen
+ 	 * USART) as well, such as PA2 and PA3. You can also split them
+	 * so PA2 for Tx, PD6 for Rx but you would have to enable both
+	 * the GPIOA and GPIOD clocks in that case
+	 */
+	gpio_mode_setup(GPIOD, GPIO_MODE_AF, GPIO_PUPD_NONE, GPIO5 | GPIO6);
+
+	/* Actual Alternate function number (in this case 7) is part
+	 * depenedent, check the data sheet for the right number to
+	 * use.
+	 */
+	gpio_set_af(GPIOD, GPIO_AF7, GPIO5 | GPIO6);
+
+	/* This then enables the clock to the USART2 peripheral which is
+	 * attached inside the chip to the APB2 bus. Different peripherals
+	 * attach to different buses, and even some UARTS are attached to
+	 * APB1 and some to APB2, again the data sheet is useful here.
+	 */
+	rcc_peripheral_enable_clock(&RCC_APB1ENR, RCC_APB1ENR_USART2EN);
+
+	/* Set up USART/UART parameters using the libopencm3 helper functions */
+	usart_set_baudrate(CONSOLE_UART, 115200);
+	usart_set_databits(CONSOLE_UART, 8);
+	usart_set_stopbits(CONSOLE_UART, USART_STOPBITS_1);
+	usart_set_mode(CONSOLE_UART, USART_MODE_TX_RX);
+	usart_set_parity(CONSOLE_UART, USART_PARITY_NONE);
+	usart_set_flow_control(CONSOLE_UART, USART_FLOWCONTROL_NONE);
+	usart_enable(CONSOLE_UART);
+
+	/* At this point our console is ready to go so we can create our
+	 * simple application to run on it.
+	 */
+	console_puts("\nUART Demonstration Application\n");
+	while (1) {
+		console_puts("Enter a string: ");
+		len = console_gets(buf, 128);
+		if (len) {
+			console_puts("\nYou entered : '");
+			console_puts(buf);
+			console_puts("'\n");
+		} else {
+			console_puts("\nNo string entered\n");
+		}
+	}
+}