STM32F411 Only running correctly in debug mode with debugger attached

[Eqqman]

We have a project running on the STM32F411 via the standard discovery board :

https://www.st.com/en/evaluation-tools/32f411ediscovery.html

It has been verified that with the STLink port plugged in the BOOT0 pin is at GND and the NRST pin is at 3V.  We are running into the apparently very common issue that code which was running perfectly fine suddenly only works in debug mode.  Code has been added to light up LD3 (the orange LED) which connects to pin PD13 on the processor.  By placing this code as high up the execution chain as possible we see that the device hangs almost immediately as soon as the clock configuration code is executing.  The code running is now as follows:

// from stm32.h
/* modify bitfield */
#define _BMD(reg, msk, val)     (reg) = (((reg) & ~(msk)) | (val))
/* set bitfield */
#define _BST(reg, bits)         (reg) = ((reg) | (bits))
/* clear bitfield */
#define _BCL(reg, bits)         (reg) = ((reg) & ~(bits))
/* wait until bitfield set */
#define _WBS(reg, bits)         while(((reg) & (bits)) == 0)
/* wait until bitfield clear */
#define _WBC(reg, bits)         while(((reg) & (bits)) != 0)
/* wait for bitfield value */
#define _WVL(reg, msk, val)     while(((reg) & (msk)) != (val))
/* bit value */
#define _BV(bit)                (0x01 << (bit))

Our code:

void LD3_Init(void) {
    _BST(RCC->AHB1ENR, RCC_AHB1ENR_GPIODEN);
    _BMD(GPIOD->MODER, (0x03 << 26), (0x01 << 26));
    _BCL(GPIOD->OTYPER, (0x01 << 13));

} // end LD3_Init

void LD3_ON(void) {
    _BST(GPIOD->ODR, (0x01 << 13));

} // end LD3_ON

int main (void) {
    volatile uint32_t reg_value;

    // Original source assumes default RCC register setting of 0x0000_XX81
    //  which enables the HSI clock, but better perhaps to explicitly set it
    _BCL(RCC->CR, RCC_CR_PLLON);
    _BCL(RCC->CR, RCC_CR_HSEON);
    _BST(RCC->CR, RCC_CR_HSION);
    _WBS(RCC->CR, RCC_CR_HSIRDY);

    do {
        _BST(RCC->APB1ENR, RCC_APB1ENR_PWREN);
        reg_value = RCC->APB1ENR;
        (void)reg_value;
    } while (0x00);

    /* set flash latency 2WS */
    _BMD(FLASH->ACR, FLASH_ACR_LATENCY, FLASH_ACR_LATENCY_2WS);
    /* setting up PLL 16MHz HSI, VCO=144MHz, PLLP = 72MHz PLLQ = 48MHz  */
    _BMD(RCC->PLLCFGR,
        RCC_PLLCFGR_PLLM | RCC_PLLCFGR_PLLN | RCC_PLLCFGR_PLLSRC | RCC_PLLCFGR_PLLQ | RCC_PLLCFGR_PLLP,
        _VAL2FLD(RCC_PLLCFGR_PLLM, 😎 | _VAL2FLD(RCC_PLLCFGR_PLLN, 72) | _VAL2FLD(RCC_PLLCFGR_PLLQ, 3));

    // Original driver also fails to set the APB1 Prescaler as the APB1 clock must run 
    //  at or below 50MHz
    RCC->CFGR &= ~((uint32_t)(0x07 << 0x0A));
    RCC->CFGR |=  ((uint32_t)(0x04 << 0x0A));
    /* enabling PLL */
    _BST(RCC->CR, RCC_CR_PLLON);
    _WBS(RCC->CR, RCC_CR_PLLRDY);
    /* switching to PLL */
    _BMD(RCC->CFGR, RCC_CFGR_SW, RCC_CFGR_SW_PLL);
    _WVL(RCC->CFGR, RCC_CFGR_SWS, RCC_CFGR_SWS_PLL);

    // wait for the clock to stabilize
    reg_value = 0x0000FFFF;
    while (reg_value) { --reg_value; };
    LD3_Init();
    LD3_ON();
    // lots of other stuff...
} // 

The rest of the code is too much to post, but this suffices to show the problem.  When stepping through the debugger, the LED turns on, but won't do so in Release mode nor run in Debug mode without the debugger stepping the code (and of course, the LED is just an obvious test output, none of the rest of our code runs either).  This issue usually relates to incorrect HW settings on the external pins but that is not the case here, and we have numerous examples of this same code to configure the clocks running in other cases perfectly without issue.  Any suggestions as to what to look at would be appreciated.

[waclawek.jan]

And if you don't switch clock to PLL, things do work as expected?

Read out and check/post content of RCC and FLASH registers. Is the default VOS setting adequate for the system frequency you are using?

This may be also a hardware problem, e.g. inadequate VCAP or problematic ground routing. Try on a"known good" board such as Nucleo.

JW

[Eqqman]

Blocking the switch to PLL input doesn't help (this wouldn't be a good solution anyway, as we need to run on the PLL clock).

The default VOS bits read 0x02 which is the correct setting (84MHz or less).  Stepping through the code we see no changes to these bits.  The reference manual indicates that the HW will set this to 0x03 on its own (100MHz or less) if you turn PLL OFF, which we're not doing via our own code.

Given that we're using the Discovery board produced and sold by ST, it would be hoped this falls into the "known good" category.  Same issue is happening on two different physical boards.

[waclawek.jan]

> Given that we're using the Discovery board

I overlooked that, sorry.

Reduce the code to absolute minimum but complete compilable and still exhibiting the problem, and post, preferrably together with the resulting .elf.

JW

[Eqqman]

The code is being generated by Segger Embedded Studio.  Using an LED as the test in Release mode to see where the code stops executing, it was traced down to this function that is part of the Segger Embedded Studio boilerplate code for setting up the C runtime environment:

START_FUNC _start
        //
        // Call linker init functions which in turn performs the following:
        // * Perform segment init
        // * Perform heap init (if used)
        // * Call constructors of global Objects (if any exist)
        //
        ldr     R4, =__SEGGER_init_table__      // Set table pointer to start of initialization table
L(RunInit):
        ldr     R0, [R4]                        // Get next initialization function from table
        adds    R4, R4, #4                      // Increment table pointer to point to function arguments
        blx     R0                              // Call initialization function
        b       L(RunInit)
MARK_FUNC __SEGGER_init_done
MARK_FUNC __startup_complete
        //
        // Time to call main(), the application entry point.
        //
#ifndef FULL_LIBRARY
        //
        // In a real embedded application ("Free-standing environment"),
        // main() does not get any arguments,
        // which means it is not necessary to init R0 and R1.
        //
        bl      APP_ENTRY_POINT                 // Call to application entry point (usually main())
END_FUNC _start

With the LED code at the start of this function, it turns on, but not if it's at the end (again, no issues though when running a debug session).  The RunInit process calls these two functions in order:

<__SEGGER_init_zero>
    6820        ldr r0, [r4]
    6861        ldr r1, [r4, #4]
    3408        adds r4, #8
    2200        movs r2, #0
    E000        b 0x08014016
    5442        strb r2, [r0, r1]
    3901        subs r1, #1
    D5FC        bpl 0x08014014
    4770        bx lr

<__SEGGER_init_copy>
    6820        ldr r0, [r4]
    6861        ldr r1, [r4, #4]
    68A2        ldr r2, [r4, #8]
    340C        adds r4, #12
    E001        b 0x08013D0E
    5C8B        ldrb r3, [r1, r2]
    5483        strb r3, [r0, r2]
    3A01        subs r2, #1
    D5FB        bpl 0x08013D0A
    4770        bx lr

With __SEGGER_init_zero being invoked many, many, times, so many I gave up trying to step through it and just ran to a break point at __SEGGER_init_copy.  So by skipping this code I can get the LED to turn on but of course nothing else in the code runs properly since the runtime environment is not correctly initialized.

Attached file is ELF with extension renamed to HEX.  Most, but not all, of our code has been removed and the problem still presets itself.

[Eqqman]

Trying to attach the file didn't work.

[waclawek.jan]

Try this:

void LD3_Init(void) {
    _BST(RCC->AHB1ENR, RCC_AHB1ENR_GPIODEN);
__NOP();
__NOP();
__NOP();
__NOP();
    _BMD(GPIOD->MODER, (0x03 << 26), (0x01 << 26));
    _BCL(GPIOD->OTYPER, (0x01 << 13));
} // end LD3_Init

as some peripherals may require some time after enabling in RCC, before they can be accessed.

JW