2x1=10

Now what a fun: Unboxed my brand new STM32F3-Dis­cov­ery, plugged it in — sweet blink­ing rap­ture. Com­piled my first demo pro­gram, played around with the timers, all was so good. Until I had a clos­er look at the sys­tem clock speed: 8 MHz it said. So I dug into the unknown grounds of STM32F3 devel­op­ment, end­ed up in the gen­er­at­ed firmware’s sys­tem ini­tial­iza­tion func­tion in system_stm32f30x.c — which looks like this:

static void SetSysClock(void)
{
    __IO uint32_t StartUpCounter = 0, HSEStatus = 0;

    /* SYSCLK, HCLK, PCLK2 and PCLK1 configuration -----------*/
    /* Enable HSE */
    RCC->CR |= ((uint32_t)RCC_CR_HSEON);

    /* Wait till HSE is ready and if Time out is reached exit */
    do
    {
        HSEStatus = RCC->CR & RCC_CR_HSERDY;
        StartUpCounter++;
    } while((HSEStatus == 0) && (StartUpCounter != HSE_STARTUP_TIMEOUT));

    if ((RCC->CR & RCC_CR_HSERDY) != RESET)
    {
        HSEStatus = (uint32_t)0x01; // all good
    }
    else
    {
        HSEStatus = (uint32_t)0x00; // nah.
    }

    /* ... */

I did so, only to find out that HSEStatus nev­er switched to 0x01 because the RCC_CR_HSERDY flag was nev­er assert­ed in the first place.

Obvi­ous­ly no one else in the whole wide web had trou­ble with this. Cold water? Let’s dive!
Some dude at the ST forums point­ed me to the trick to out­put the RCC clock sig­nal to the board’s PA8 pin, which I did like so:

void InitializeMCOGPIO() {
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);

    /* Configure MCO (PA8) */
    GPIO_InitTypeDef gpioStructure;
    gpioStructure.GPIO_Pin = GPIO_Pin_8;
    gpioStructure.GPIO_Speed = GPIO_Speed_50MHz;
    gpioStructure.GPIO_Mode = GPIO_Mode_AF;
    gpioStructure.GPIO_OType = GPIO_OType_PP;
    gpioStructure.GPIO_PuPd = GPIO_PuPd_NOPULL ;
    GPIO_Init(GPIOA, &gpioStructure);

    /* Output HSE clock on MCO pin (PA8) */
    RCC_MCOConfig(RCC_MCOSource_HSE);
}

Turned out … well, noth­ing. Flat­line on that pin. So I took my mul­ti­me­ter and went upstream from the oscil­la­tor pins. Sol­der bridge SB12, of course bridged, work­ing fine, SB17 open as request­ed, and then — silence on RB48. No beeps on my meter, no val­ue, just plain high imped­ance.

To make a long sto­ry short: That 100 Ω resis­tor was borked, so I replaced it with some spare parts of an old scan­ner board I had float­ing around in the to-do stash. I’m not exact­ly known for mas­sive sol­der­ing expe­ri­ence, but this video helped a lot here.

Final result:

Ugly but effec­tive. Works like a charm now.