Mesa 6i25: Troubleshooting Missing 7i77 Analog I/O

A LinuxCNC retrofit using a Mesa 6i25 with 7i77 and 7i76 daughtercards can show digital I/O in PNCconf while omitting the 7i77 analog-output and encoder configuration panes. The evidence identifies two separate checks: confirm the FPGA firmware matches the daughtercard combination, then test PNCconf under an English Debian locale. In the reported Debian 10 Buster, PREEMPT-RT, LinuxCNC 2.8.2 installation, changing the interface from French to English restored the missing panes.

Identify the Failure Mode

Separate Firmware Mapping from the Locale Defect

Do not treat the missing panes as a single-cause failure. The 6i25 must first expose the correct I/O mapping for both daughtercards. The recorded firmware package contains 5i25_7i77_7i76.bit for programming and 5i25_7i77_7i76.pin for reviewing the expected I/O assignment. Although the installed board is identified as a 6i25, the supplied filenames use the 5i25 prefix; preserve the package filename instead of silently renaming it.

If firmware readback matches the pin file but PNCconf still omits the analog-output and encoder pages, switch the Debian interface to English. Reinstalling Debian did not correct the reported behavior, while changing the locale did.

Verify and Load the FPGA Firmware

Install, power, and configure the Mesa card before running the firmware utility. The evidence records the following Mesaflash sequence. Confirm the command syntax supported by the installed Mesaflash package before use because no official command reference was supplied with the case.

1. Place 5i25_7i77_7i76.bit in the command's accessible working path. A file-not-found error occurred until the bitstream was placed where Mesaflash could locate it.
2. Read the current mapping and compare the output with 5i25_7i77_7i76.pin.

   sudo mesaflash device --5i25 --readmid

3. If the mapping is wrong, perform the recorded fallback write, reload, and readback.

   sudo mesaflash device --5i25 --fallback --write 5i25_7i77_7i76.bit
   sudo mesaflash device --5i25 --fallback --reload
   sudo mesaflash device --5i25 --readmid

4. Only after the fallback image produces the expected mapping, perform the recorded permanent write and verify it again.

   sudo mesaflash device --5i25 --write 5i25_7i77_7i76.bit
   sudo mesaflash device --5i25 --reload
   sudo mesaflash device --5i25 --readmid

Restore the Missing PNCconf Pages

1. Start PNCconf and select the 7i77_7i76 configuration.
2. If only digital I/O appears, change Debian from French to English and restart PNCconf.
3. Confirm that the 7i77 pane labeled PWM and the encoder configuration pane are now present.
4. Create the initial machine configuration in English. After generation, return Debian to French if required; the reported system retained operation even though the localized configuration-window problem remained.
5. For later customization, edit the generated INI and HAL files directly instead of depending exclusively on the configuration utility.

Verify Hardware and Configuration

Use three independent acceptance checks. First, Mesaflash readback must correspond to the I/O assignments documented in 5i25_7i77_7i76.pin. Second, PNCconf in English must display both the 7i77 analog-output/PWM pane and the encoder pane. Third, connect an encoder and verify that LinuxCNC reports its motion; the reported installation passed this encoder test after the panes became available.

Do not proceed from a visible digital-I/O list alone. It confirms only that some configuration data is available, not that the required analog and encoder functions have been exposed and configured.

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