MCU Protocol Command 0xC1 failed

mangOH Yellow
1

I also posted this request over on the Sierra forum, hope you don’t mind me duplicating it here:

I’m running into an issue with the WP7702 on a mangOH Yellow. I’m going into ultra low power mode and waking up when the ADC reading is above a threshold. A few times, I have been able to get the modem into a state where the internal MCU seems to stop responding. The I2C bus still seems fine because it’s still taking to other chips on the I2C bus fine, but the internal I2C communications to the MCU fail:

[   36.793392] MCU Protocol Command 0xC1 failed, retry=1
[   36.804479] MCU Protocol Command 0xC1 failed, retry=2
[   37.322292] MCU Protocol Command 0xC1 failed, retry=3
[   37.844914] MCU Protocol Command 0xC1 failed, retry=4
[   38.365039] MCU Protocol Command 0xC1 failed, retry=5
[   38.884934] MCU Protocol Command 0xC1 failed, retry=6
[   39.402401] MCU Protocol Command 0xC1 failed, retry=7
[   39.924921] MCU Protocol Command 0xC1 failed, retry=8
[   40.445489] MCU Protocol Command 0xC1 failed, retry=9
[   40.964935] MCU Protocol Command 0xC1 failed, retry=10
[   41.484742] MCU Protocol Command 0xC1 failed, retry=11

Rebooting doesn’t fix it, so the modem gets stuck in this state with no possible way of recovering. Here is info about my versions:

root@swi-mdm9x28-wp:~# cm info
Device:                        WP7702
IMEI:                          352653090203043
IMEISV:                        4
FSN:                           4L935170120410
Firmware Version:              SWI9X06Y_02.32.02.00 c2e98c jenkins 2019/08/30 07:28:21
Bootloader Version:            SWI9X06Y_02.32.02.00 c2e98c jenkins 2019/08/30 07:28:21
MCU Version:                   002.013
PRI Part Number (PN):          9909138
PRI Revision:                  001.001 
Carrier PRI Name:              SIERRA
Carrier PRI Revision:          001.027_000
SKU:                           1104405
Last Reset Cause:              Power Down
Resets Count:                  Expected: 152    Unexpected: 1

I’ve also seen other commands fail, like 0xCA. Sometimes it ends in the module constantly rebooting over and over again, and sometimes it ends in the module being stuck in ULPM with no way to wake it up.

Has anyone else ever seen this problem? This is a showstopper for our product, and I’m surprised that I couldn’t find any other references to this error message on Google.