Feature: samd: Implemented support for the SAMC21 series

[koendv]

Detailed description

This PR adds a new target: Atmel SAMC21.

• The PR was tested on a Atmel SAMC21N18A (rev E) M0+, with parameters:

  • did: 0x11011420
  • family: 2
  • series: 1
  • devsel: 32

• SAMD_DID_MASK was changed from 0xff380000U to 0xfe380000U.
  This allows SAMC21 parts where DID begins with 0x11 to be accepted.

• SAMD_DID_FAMILY_MASK was changed from 0x3fU to 0x1fU.
  According to the datasheet, the field "family" in the DID Device Identification Register is a 5 bit field, so the mask ought to be 0x1f, not 0x3f.

• sample gdb session attached:
  samc21.txt

Your checklist for this pull request

• I've read the Code of Conduct
• I've read the guidelines for contributing to this repository
• It builds for hardware native (make PROBE_HOST=native)
• It builds as BMDA (make PROBE_HOST=hosted)
• I've tested it to the best of my ability
• My commit messages provide a useful short description of what the commits do

Closing issues

fixes #890

[dragonmux]

Before we go and review this, please correct your commit message to comply with the contribution guidelines. This modifies the file samd.c in the target tree, so should be suffixed like: samd: Implemented support for the SAMC21 series.

[dragonmux]

There are a couple of items to address, one of which technical rather than stylistic. With those addressed and the commit message point sorted, this looks good and we'll be happy to accept the PR.

[dragonmux]

This now needs rebasing on main due to #1662, but once done we'll mark it as accepted and merge. Thank you for fixing those issues.

[koendv]

OK, thanks.
FYI: A side issue. When I connect to an SAMC21, sometimes "mon swd" is instantaneous; sometimes there is a 2 second delay. If there is a delay when connecting, BMDA the gives the following message:

koen@nuc:~/src/blackmagic$ ./src/blackmagic 
Listening on TCP port: 2000
Halt via DHCSR(02000001): failure after 2001ms
Try again with longer timeout or connect under reset
adiv5: Failed to prepare AP, results may be unpredictable

If I then try "mon swd" a second time it's instantaneous; no error message; works fine.
This is just FYI.

[dragonmux]

Please could you use BMDA and run src/blackmagic -tv 5 twice in a row, capturing the log both times, so we can look into that and see what's going on there as that DHCSR value does indeed show the core not halting for some reason. Please open a new issue ticket with your results.