[reset] Reset and force debug for Cortex M0 targets

[mlu]

It seems that for CortexM0 targets, tested with STM32L053, memory and memory mapped registers cannot be accesed with _stlink_usb_read_debug32 unless the core is halted in debug state after a call to stlink_force_debug(sl). Resetting the core seems to start it again. This has implications for how we can identify the chip reading the cip-id registers.

For cortex M3 and M4 the memory is accessible from the debugger while the core and a program is running so this is not an issue for these cores.

Now the three programs st-util, st-flash and st-info have different behavior and therefore works and fails under different circumstances, making the situation confusing.

st-util normally halts and enters debug mode before handing control to gdb, and calls open with resetflag 0, stlink_open_usb(state.logging_level, 0); and it correctly identifies STM32L053

st-flash must enter debug mode to run RAM based flash loaders, calls open with reset flag 1, stlink_open_usb(state.logging_level, 1); and it fails to identify STM32L053

st-info calls open with reset flag 1, stlink_open_usb(state.logging_level, 1); and it fails to identify STM32L053

This is a bit of a mess and it should be cleaned up, so input is wanted, we dont want to break what is working.

[xor-gate]

This should be fixed in latest v1.2.0 and master, could you verify?

[Ant-ON]

@Nightwalker-87
I think it might be closed by #1114
The behavior is now more standardized. All applications are called with reset 1 (normal). You can switch to reset 2 (connect under reset) by command line argument. st-info and st-util can use reset 0 (hot plug).

[Nightwalker-87]

I think this should be documented before we close this issue.

[Ant-ON]

@Nightwalker-87 I added information about args to https://github.com/stlink-org/stlink/blob/develop/doc/tutorial.md

[Nightwalker-87]

@Ant-ON I have taken note of that, but was pointing at

The behavior is now more standardized. All applications are called with reset 1 (normal). You can switch to reset 2 (connect under reset) by command line argument. st-info and st-util can use reset 0 (hot plug).

on the code-layer and not on the command line level.

[Ant-ON]

@Nightwalker-87 in command line layer too. See --hot-plug and --connect-under-reset in tutorial.md.
I no added the --connect-under-reset to gdb. I don't know how to do it there yet. I will add the --hot-plug to the st-flash at evning.

[Nightwalker-87]

Ah now I get it - reset 0, 1 & 2 sounded like enum cases in the code to me at first... That's fine then.
I was aware of the mentioned command options being listed in the tutorial, as you mentioned it above.

[Nightwalker-87]

As #1114, which addresses this ticket, also includes the related documentation, we can now close this issue as resolved.