IO port always readuing 0v in release mode.

[SSmit.13]

Hi

  I am using a STM32L433 and have a digital input pin, which is checked on bootup and enables the USB if 3.3v is in the pin.  When working in debug mode, it always works, but when I switch to release mode , using stm32CubeIDE , it always reads 0v, and my optimization is None. Below is my code .

 

 

RCC->AHB2ENR |= RCC_AHB2ENR_GPIOBEN; //Enable Port B clock

GPIOB->MODER &= ~GPIO_MODER_MODE12; //PB12 as input, check for usb interaction
inSetupMode=(GPIOB->IDR >> 12 )& 1; //=1 when using USB

 

 

Can anyone let me know what the issue is?

 

Many thanks

 

Scott

[Tesla DeLorean]

Hard to know.

Enable the clocks early. There is a hazard enabling the clock and then immediately writing the peripheral registers.

Read back the RCC->AHB2ENR  /  _DSB()

[SSmit.13]

Hi ,

what is _DSB?

 

What do I check ? Is it if the B clock is enabled?

 

And if its not what do I do if its not enabled?

 

Sorry for all the questions.

 

Scott

 

[gbm]

Not a check, just small delay. Also, I would suggest adding some small delay between MODER setting and reading the IDR.

[SSmit.13]

Many thanks for the reply. I will add a delay.

 

Thanks

Scott

 

[SSmit.13]

I added the line:

__DSB();

after the clocks being enabled, but never made a difference.

 

But when I added a 2ms delay after GPIOB->MODE and this worked.

Where do I add the DSB command, and is it just the DSB() on its own?

CHeers

Scott

 

[Tesla DeLorean]

After the write

See how HAL does the clock enables, reads back to insure writes complete first, as forces IN-ORDER-COMPLETION for the write buffers and pipeline, and adds perhaps 4 bus cycles to the transaction.

#define __HAL_RCC_GPIOB_CLK_ENABLE() do { \
 __IO uint32_t tmpreg; \
 SET_BIT(RCC->IOPENR, RCC_IOPENR_GPIOBEN); \
 /* Delay after an RCC peripheral clock enabling */ \
 tmpreg = READ_BIT(RCC->IOPENR, RCC_IOPENR_GPIOBEN); \
 UNUSED(tmpreg); \
 } while(0U)