The SPI-MEMS example, its not great but it does use the SPI

port and can tell you the temperature of the room you are in.

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

@@ -0,0 +1,54 @@
+/*
+ * 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/>.
+ */
+
+#ifndef __CONSOLE_H
+#define __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. 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
+
+/*
+ * 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(int baudrate);
+
+/* this is for fun, if you type ^C to this example it will reset */
+#define RESET_ON_CTRLC
+
+#endif