Detailed description
- This is a minor new feature.
- The problem is rudimentary/poor implementation of
jtagtap_cycle()in jlink.c backend used by BMDA. (and it didn't even exist until very recently) - This PR solves it by providing one moderately optimized variant.
Tracking: #2180.
Note that jlink_jtag_init() used to rely on a direct jlink_transfer() of a baked byte buffer with 56 idle clocks and SWD-to-JTAG switch sequence, I replaced that with a jlink_jtag_cycle() call for 56-5=51 clocks and a shorter, 16-bit sequence. The caveat is that new function may raise an exception, and at scan time it results in immediate SIGABRT because it's unhandled (by any TRY-CATCH up the callsite). It also happens to be the first 0xCF opcode transfer. If such behaviour is unwanted, discard commit 1.
Tested on J-Link V9 against a RISC-V MCU.
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 (see Building the firmware)
- It builds as BMDA (see Building the BMDA)
- 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
## Detailed description
* This is a minor new feature.
* The problem is rudimentary/poor implementation of `jtagtap_cycle()` in jlink.c backend used by BMDA. (and it didn't even exist until very recently)
* This PR solves it by providing one moderately optimized variant.
Tracking: #2180.
Note that `jlink_jtag_init()` used to rely on a direct `jlink_transfer()` of a baked byte buffer with 56 idle clocks and SWD-to-JTAG switch sequence, I replaced that with a `jlink_jtag_cycle()` call for 56-5=51 clocks and a shorter, 16-bit sequence. The caveat is that new function may raise an exception, and at scan time it results in immediate SIGABRT because it's unhandled (by any TRY-CATCH up the callsite). It also happens to be the first 0xCF opcode transfer. If such behaviour is unwanted, discard commit 1.
Tested on J-Link V9 against a RISC-V MCU.
## Your checklist for this pull request
* [x] I've read the [Code of Conduct](https://github.com/blackmagic-debug/blackmagic/blob/main/CODE_OF_CONDUCT.md)
* [x] I've read the [guidelines for contributing](https://github.com/blackmagic-debug/blackmagic/blob/main/CONTRIBUTING.md) to this repository
* [x] It builds for hardware native (see [Building the firmware](https://github.com/blackmagic-debug/blackmagic?tab=readme-ov-file#building-black-magic-debug-firmware))
* [x] It builds as BMDA (see [Building the BMDA](https://github.com/blackmagic-debug/blackmagic?tab=readme-ov-file#building-black-magic-debug-app))
* [x] I've tested it to the best of my ability
* [x] My commit messages provide a useful short description of what the commits do
## Closing issues