Arduino for STM32

BJHenry wrote: Thu Feb 27, 2020 8:19 am My understanding was the STM32s will look for an external clock source, and if there isn't one they'll default to using the internal RC.

Just4Fun wrote: Thu Feb 27, 2020 1:23 pm If I remember well, driving BOOT0 to 3.3V will start the internal serial bootloader for ever.
In this way, after every reset you will start the internal bootloader, not your "user" program...

So may be better:

1) disconnect NRST from the serial-usb DTR
2) reset the stm32 (BOOT0 = 3.3V -> Serial bootloader activated)
3) upload the "user" program with arduino (serial bootloader)
4) jumper BOOT0 to GND ( -> execute "user" program from flash)
5) reset.

Now your blink test should work...

stevestrong wrote: Thu Feb 27, 2020 1:40 pm

BJHenry wrote: Thu Feb 27, 2020 8:19 am My understanding was the STM32s will look for an external clock source, and if there isn't one they'll default to using the internal RC.

That is wrong.
The system clock must be selected manually in the clock configuration register RCC_CFGR. The parameter SW (System Clock Switch) is responsible to select HSI (internal 8 MHz clock), HSE (external quartz) or PLL. Have a look into RM0360 chapter 7.

If you don't have any external resonator components, you have to set SW to 00.
This is the default value, but you have to check whether your application or core startup files will change this value or not.

7.2.6 System clock (SYSCLK) selectionVarious clock sources can be used to drive the system clock (SYSCLK):HSI oscillatorHSE oscillatorPLLAfter a system reset, the HSI oscillator is selected as system clock. When a clock source is used directly or through the PLL as a system clock, it is not possible to stop it.A switch from one clock source to another occurs only if the target clock source is ready (clock stable after startup delay or PLL locked). If a clock source which is not yet ready is selected, the switch will occur when the clock source becomes ready.

/**
* Description: This function enables the interrupt on HSE ready,
*
 and start the HSE as external clock.
*/
__INLINE void StartHSE(void)
{
/* Configure NVIC for RCC */
/* (1) Enable Interrupt on RCC */
/* (2) Set priority for RCC */
NVIC_EnableIRQ(RCC_CRS_IRQn); /* (1)*/
NVIC_SetPriority(RCC_CRS_IRQn,0); /* (2) */
/* (1) Enable interrupt on HSE ready */
/* (2) Enable the CSS
Enable the HSE and set HSEBYP to use the external clock
instead of an oscillator
Enable HSE */
/* Note : the clock is switched to HSE in the RCC_CRS_IRQHandler ISR */
RCC->CIR |= RCC_CIR_HSERDYIE; /* (1) */
RCC->CR |= RCC_CR_CSSON | RCC_CR_HSEBYP | RCC_CR_HSEON; /* (2) */
}

1. To modify the PLL configuration, proceed as follows:
2. Disable the PLL by setting PLLON to 0.
3. Wait until PLLRDY is cleared. The PLL is now fully stopped.
4. Change the desired parameter.
5. Enable the PLL again by setting PLLON to 1.
6. Wait until PLLRDY is set.

BJHenry wrote: Tue Mar 03, 2020 5:14 am
You were on the money. After the upload has finished I can ground the BOOT0 pin and reset the MCU to make it work.
This behaviour is different to what I've seen on an STM32F103C8 that I've used on another project- with that one it automatically starts the user code after upload is finished.

BJHenry wrote: Tue Mar 03, 2020 5:14 am ...I took this to mean that it wouldn't change from internal to external oscillator until the external one was up and running satisfactorily.

BJHenry wrote: Tue Mar 03, 2020 5:14 am ...I took this to mean that it wouldn't change from internal to external oscillator until the external one was up and running satisfactorily.