STM32F407 debuugger not working when PORTA in use

[Mark Greally]

Posted on October 10, 2017 at 12:42

Hi.

Using a STM32F407 I am having an issue using the debugger when PORTA is in use. The debugger works fine when PORTA is not in use. I am using MCO1 which is on PORTA and when I set the MODER register the debugger fails.

    // Enable MCO1 clock on PA8

     GPIOA->MODER = (1 << 17);  // same as *GPIOAMODER = (1 << 17);     GPIOA->OSPEEDR = 0x30000;  // very high speed. OSPEEDR8     GPIOA->PUPDR = 0x0;        // No pull-up, pull-down     GPIOA->AFR[0] = 0x0;       // AF0     GPIOA->AFR[1] = 0x0;       // AF0

PA8 does not share any pins with the debugger so this should work. Is there some additional settings that need to be set to allow this??

Thanks.

[waclawek.jan]

Posted on October 10, 2017 at 12:51

Don't override MODER/AFRL/H for the SWD/JTAG pins (nor other GPIO registers for those pins).

Hint: look at their default values.

JW

[Mark Greally]

Posted on October 10, 2017 at 14:56

Thanks Guys. I replaced the first line with GPIOA->MODER |= (1 << 17); to set the individual bit and it works now. I thought the pins P13, P14 and P15 defaulted to 00 not 01. Its not very clear in the RM.

[Mark Greally]

Posted on October 10, 2017 at 13:13

Removing the alternate function code has no affect. The code works fine when not in debug mode as it should, The MCO clock is generating as it should. I also tried MCO2 which is on PORTC and debug mode works then when PORTA is not in use. Its only PORTA when in debug mode that it doesn't work. I have isolated it to: 

GPIOA->MODER = (1 << 17); 

It works for all other lines but of course I need the above for the clock. This is really strange because as soon as I program in non debug mode it works fine. Does setting the MODER (in PORTA) register somehow disable debugging mode?

[Tesla DeLorean]

Posted on October 10, 2017 at 14:05

Yes, because 

GPIOA->MODER = (1 << 17); nukes the ENTIRE register of its existing content, and the debug interface uses PA13/PA14. Perhaps you should modify the content while respecting the bits you aren't looking to change?

[waclawek.jan]

Posted on October 10, 2017 at 14:06

I've told you above: don't override the debug pins' settings in GPIO.

Those two pins have to be  set as AF in MODER (plus their AFRL/AFRH setting as AF0 and OSPEDR as... some of the high speed).

Read the GPIO chapter in RM. And use the default values.

JW

[waclawek.jan]

Posted on October 10, 2017 at 15:15

They default to 10 and not 01.

Also, you don't want to override their OSPEEDR settings too.

JW

[Mark Greally]

Posted on October 10, 2017 at 15:43

Sorry my typo, thanks.

[Tesla DeLorean]

Posted on October 10, 2017 at 16:56

Also the debugger can change clock and pin configurations to suit it's needs, so things might not always be in reset/default conditions.

You should mask off the content, and change the specific bits of interest for PA8 vs PA[0..15]

[Mark Greally]

Posted on October 10, 2017 at 17:42

Thanks, I will keep this in mind.