Fix JTAG sanity check in BYPASS device counting #2178

ALTracer commented 2026年01月24日 11:23:28 +01:00 (Migrated from github.com)

Detailed description

• This is not a new feature.
• The existing problem is an error triggered in BMD logic for chips which are debuggable by OpenOCD using same adapteres.
• The PR solves it by ensuring DR value is predictable.

jtag_scan: Sanity check failed: BYPASS dev count doesn't match IR scan
Not tested yet. The error/warning demotion will be rebased away once I confirm the solution works.
Upd: tested to improve the situation, the chip in question became scannable by BMF. Sanity check restored.

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 not a new feature. * The existing problem is an error triggered in BMD logic for chips which are debuggable by OpenOCD using same adapteres. * The PR solves it by ensuring DR value is predictable. `jtag_scan: Sanity check failed: BYPASS dev count doesn't match IR scan` Not tested yet. The error/warning demotion will be rebased away once I confirm the solution works. Upd: tested to improve the situation, the chip in question became scannable by BMF. Sanity check restored. ## 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

ALTracer commented 2026年01月26日 17:07:32 +01:00 (Migrated from github.com)

Logs with a FT2232H-attached board (unsupported) on this branch. Please state whether I should keep or discard the jtag_scan: DR=1 by default in BYPASS message, which confirms such chips exist.

$ ./build/blackmagic -tjv 1 -c ftdijtag
Black Magic Debug App v2.0.0-304-g11bd1f2c
 for Black Magic Probe, ST-Link v2 and v3, CMSIS-DAP, J-Link, FTDI (MPSSE) and WCH-Link
Using 0403:6010 <no serial number> FTDI
 Dual RS232-HS ---
Running in Test Mode
Target voltage: Unknown
Speed set to 3.750MHz for JTAG
Resetting TAP
Change state to Shift-DR
Scanning out ID codes
Return to Run-Test/Idle
Change state to Shift-IR
Scanning out IRs
Return to Run-Test/Idle
Change state to Shift-DR
jtag_scan: DR=1 by default in BYPASS
Return to Run-Test/Idle
ID code 0x000006df: Unknown
Given target number 1 not available max 0

Logs with a FT2232H-attached board (unsupported) on this branch. Please state whether I should keep or discard the `jtag_scan: DR=1 by default in BYPASS` message, which confirms such chips exist. ```c $ ./build/blackmagic -tjv 1 -c ftdijtag Black Magic Debug App v2.0.0-304-g11bd1f2c for Black Magic Probe, ST-Link v2 and v3, CMSIS-DAP, J-Link, FTDI (MPSSE) and WCH-Link Using 0403:6010 <no serial number> FTDI Dual RS232-HS --- Running in Test Mode Target voltage: Unknown Speed set to 3.750MHz for JTAG Resetting TAP Change state to Shift-DR Scanning out ID codes Return to Run-Test/Idle Change state to Shift-IR Scanning out IRs Return to Run-Test/Idle Change state to Shift-DR jtag_scan: DR=1 by default in BYPASS Return to Run-Test/Idle ID code 0x000006df: Unknown Given target number 1 not available max 0 ```

dragonmux commented 2026年01月26日 17:08:49 +01:00

You've been able to prove the purpose of this PR with that message but we don't think it adds anything to scans more generally, so please drop the extra logging message.

You've been able to prove the purpose of this PR with that message but we don't think it adds anything to scans more generally, so please drop the extra logging message.