is F407 discovery serial pll correct?

Limited support for STM32F4 Discovery, Nucleo and custom F4 boards
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Joined: Mon Nov 21, 2016 6:34 pm

is F407 discovery serial pll correct?

Post by holla2040 » Mon Nov 21, 2016 7:01 pm


Has anyone got Serial.println on the stm32f4 discovery without USB to work correctly? I'm having a baud rate problem here. I did find this post,, which says it works but my results are different.

Here's my setup
#define LED PD12

void setup() {
pinMode(LED, OUTPUT);

void loop() {
digitalWrite(LED, !digitalRead(LED));

I'm running arduino 1.6.12 on ubuntu 16.04

pin PA9 (serial1tx) connected to 3.3V ttl serial-usb dongle rx. I verified my setup with an old arduino nano, that works.

using the stm32f4 discovery board, I see garbage on the terminal screen, but I am getting chars once a secong but wrong baud rate.

I poked around and found this posting ... tviews=397

which mentions the f407 discovery board uses a 8MHz clock source not 25MHz. I started looking at stm32arduino code
Arduino/hardware/Arduino_STM32/STM32F4/cores/maple/libmaple/rccF2.c. I think function rcc_clk_init2 sets up the PLL, but I'm not very familiar with the arm at this level.

Can someone point me to which PLL register to investigate? CFGR? PLLCFGR?


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