Bootloader troubleshooting

DOCon.1 · ‎2020-09-29

Hello. I'm using an STM32F3, and am struggling to get the bootloader working on my custom board. It works on the F3 discovery board (If you remove SB19 and wire up a pull-high).

Steps: Plug USB port into PC. Boot1 is confirmed to be set high in MCU software. Pull Boot0 to +3V3 using a 10K PU. Cycle power or reset. What should happen: MCU doesn't boot normal program. PC (eg Windows) Device manager should show `STM32Bootloader`, and DFU-util can be used to flash. This is what happens on the discovery.

On my board, it boots up as normal, and Windows can't see the bootloader.

Additional data: I can confirm there's a working HSE, and the data lines work. And something weird: When I use a scope, Boot0 is reading low with the 10KPU... It only goes high if I wire it directly to a 3V3 line. (This is only on my board; dev board shows normal). This is very odd, and implies the MCU is pulling Boot0 low... which I don't think it should do.

Thank you.

TDK · ‎2020-09-29

If BOOT0 is low despite a 10kOhm pullup, and the chip is under reset (NRST low), there's a hardware issue somewhere. I'd sort that out before you tackle debugging the bootloader. Check resistance between BOOT0 and ground. It should be well over 10kOhm. Possibly a solder bridge or similar short somewhere.

> I can confirm there's a working HSE, and the data lines work.

How do you know this? You're able to load and run programs okay, just not boot to the bootloader?

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TDK · ‎2020-09-29

If BOOT0 is low despite a 10kOhm pullup, and the chip is under reset (NRST low), there's a hardware issue somewhere. I'd sort that out before you tackle debugging the bootloader. Check resistance between BOOT0 and ground. It should be well over 10kOhm. Possibly a solder bridge or similar short somewhere.

> I can confirm there's a working HSE, and the data lines work.

How do you know this? You're able to load and run programs okay, just not boot to the bootloader?

If you feel a post has answered your question, please click "Accept as Solution".

DOCon.1 · ‎2020-09-29

The boot0 reading low issue is weird. I've read boot0 is read only... It's like that on several revisions of my board, and I can't find an obvious hardware problem that would lead to it. I'll check the resistance. It's wired through a button, so I can try removing the button and seeing what the deal is. Of note, when I pull it high without a resistor, the device doesn't do its normal activity (Which is expected), but doesn't show as a bootloader.

I know the HSE/data lines work because I can communicate with the computer using USB-Serial.

Does the Boot1 bit persist when no power's applied? It's set when I load a program to check on both dev, and my boards.

DOCon.1 · ‎2020-09-29

Solved! This was indeed something with the pulling low. I removed the button, and it now works! Due to me not understanding how 4-pin buttons work.