stm32/h7: Implemented support for the HSI48

include/libopencm3/stm32/h7/rcc.h

@@ -770,6 +770,13 @@ BEGIN_DECLS
  */
 void rcc_clock_setup_pll(const struct rcc_pll_config *config);
 
+/**
+ * Setup and bring up the HSI48 for use by the USB controller.
+ *
+ * Note: Should be used with the CRS for stability
+ */
+void rcc_clock_setup_hsi48(void);
+
 /**
  * Get the clock rate (in Hz) of the specified clock source. There are
  * numerous clock sources and configurations on the H7, so rates for each

lib/stm32/h7/rcc.c

@@ -226,6 +226,13 @@ void rcc_clock_setup_pll(const struct rcc_pll_config *config) {
 	}
 }
 
+void rcc_clock_setup_hsi48(void)
+{
+	RCC_CR |= RCC_CR_HSI48ON;
+	while (!(RCC_CR & RCC_CR_HSI48RDY))
+		continue;
+}
+
 uint32_t rcc_get_bus_clk_freq(enum rcc_clock_source source) {
 	uint32_t clksel;
 	switch (source) {