[feature] Add "Connect under Reset" option

[Gamadril]

• Programmer/board type: e.g Stlink/v2-onboard
• Programmer firmware version: e.g STSW-LINK007 2.27.15
• Operating system: Mac OS X
• Stlink tools version and/or git commit hash: 1.3.1-9-gc04df7f
• Stlink commandline tool name: st-flash
• Target chip (and optional board): e.g STM32F030F4

SWCLK and SWDIO pins of my mcu are used and configured as output. That means to program the flash I have to use the "Connect Under Reset" option. This option seems to be missing. At least adding --reset does not help in that case.

[xor-gate]

Connect under reset is not to difficult the stlink has a command to assert the nRST pin and then try to connect. But this needs to be implemented.

[iglooom]

I have a same trouble and use this workaround iglooom@19381ff
It is not fully "connect under reset", but working for me.

[xor-gate]

The nRST reset pin is assert differently. I'm not sure what the output state of the pin is in your commit. First we need to measure and then implement a fix which works for everybody.

[geoffreymbrown]

I also needed this functionality. While I added it to my own copy of the repo, it'd be nice if it made it in somehow. Here are the issues in stlink_open_usb:

1. Reset has to be asserted before any mode change can happen
2. It's somewhat less than optimal that stlink_load_device_params(sl); happens in this routine, since loading flash parameters doesn't seem to work under reset.

Here's what I changed --

1. reset parameter from bool to number : values 0,1 keep current behavior. reset == 2 is used to change the following code :

    if (stlink_current_mode(sl) != STLINK_DEV_DEBUG_MODE) stlink_enter_swd_mode(sl);

    if (reset) {
        if ( sl->version.stlink_v > 1) stlink_jtag_reset(sl, 2);
        stlink_reset(sl);
        usleep(10000);
    }`

To:

   if (reset == 2)  stlink_jtag_reset(sl,0);
   if (stlink_current_mode(sl) != STLINK_DEV_DEBUG_MODE) stlink_enter_swd_mode(sl);

    if (reset == 1) {
        if ( sl->version.stlink_v > 1) stlink_jtag_reset(sl, 2);
        stlink_reset(sl);
        usleep(10000);
    }

[Nightwalker-87]

@geoffreymbrown: What about proposing a PR?

[geoffreymbrown]

The various existing apps wouldn't automatically make use of it, but anything using the library could.
I'm happy to propose a narrow PR (just the changes to make this work)
Geoffrey