Prevent MCU from booting between pymcuprog commands?

[nabelekt]

I run two commands in sequence:

pymcuprog write  --tool uart --uart /dev/ttyUSB0 --clk 230400 --device avr128da32 --memory fuses --offset 0x05 --literal 0xCC
pymcuprog write  --tool uart --uart /dev/ttyUSB0 --clk 230400 --device avr128da32 --filename gnss_power_test_psmoo.hex --erase

and may add:

pymcuprog verify --tool uart --uart /dev/ttyUSB0 --clk 230400 --device avr128da32 --filename gnss_power_test_psmoo.hex

I do this very often. My problem is that between the two commands, the previous program starts running. I need it not to. Is there any way to prevent this programmatically, and keep the MCU from booting between commands? I think maybe the RESET line would need to be held LOW?

Thanks for this tool! It is immensely helpful.

[xedbg]

Hi @nabelekt - unfortunately there is currently no way to prevent the MCU from running. A modern AVR does not always have a RESET line, and its also not known whether the debugger even has control over it.
Since fuses are not erased by a chip erase on an AVR, is it an option to use the --erase command on the fuse write (after which the MCU will run NOPs) and then write the flash on the second command without --erase? Alternatively you could use an intel-hex tool to combine the fuses into the flash image...

[nabelekt]

Thanks for the suggestion, @xedbg. I finally got around to giving it a go. I tried running this as my first command

pymcuprog write  --tool uart --uart /dev/ttyUSB0 --clk 230400 --device avr128da32 --memory fuses --offset 0x05 --literal 0xCC --erase

But that returned the error here:

Connecting to SerialUPDI
Pinging device...
Ping response: 1E9709
pymcuprog.pymcuprog_main - ERROR - Erase switch (--erase) is only supported when writing a hex file!

I figure I can do this instead:

pymcuprog erase  --tool uart --uart /dev/ttyUSB0 --clk 230400 --device avr128da32
pymcuprog write  --tool uart --uart /dev/ttyUSB0 --clk 230400 --device avr128da32 --memory fuses --offset 0x05 --literal 0xCC
pymcuprog write  --tool uart --uart /dev/ttyUSB0 --clk 230400 --device avr128da32 --filename 2_USART.hex

It makes the programming process longer than I'd like, but it does work. Any particular reason why we can't erase when writing fuses?
Any other suggestions?
Thanks!

[xedbg]

@nabelekt - I think we just did not consider this use-case when adding the --literal write. We can consider this as a feature-request going forward.
Regarding programming 'speed' - have you tried tweaking the --uart-timeout TIMEOUT argument? This could at least reduce the initial handshake time.

[nabelekt]

I think we just did not consider this use-case when adding the --literal write. We can consider this as a feature-request going forward.

Please do. It would also be great if we could write both fuses and a program in a single command.

Regarding programming 'speed' - have you tried tweaking the --uart-timeout TIMEOUT argument? This could at least reduce the initial handshake time.

This indeed does help quite a bit! --uart-timeout 0.1 on each command seems to be working well for me. Thank you!