# I2C bus driver issues on VOXL2 SLPI

Source: https://forum.modalai.com/topic/3029/i2c-bus-driver-issues-on-voxl2-slpi
Category: General Questions (https://forum.modalai.com/category/2/general-questions)
Posted: 2024-01-18 19:32:38 UTC by brahim
Replies: 2 · Views: 815

## brahim · 2024-01-18 19:32:38 UTC

I am developing a driver for an external i2c sensor and using **J19 pins 7 & 8.** ( SSC_QUP3)

When I start the driver I am doing so like this: 
"qshell xm125_evk start -X -b 4"

Assuming  "SSC_QUP3" is i2c bus 4 (correct me if I am wrong). I am using the external device i2c address correctly in the driver and on another non-voxl platform I can confirm this i2c address with i2cdetect. 

When I include the bus number at driver instantiation it will timeout and I won't see any output on mini-dm. However if I leave off the bus # it will start the driver but fail to probe and I get a bunch of read register fails at the voxl-px4 driver level while receiving the following on mini-dm:
```
[08500/02]  23:37.838  0044:01: SDSP: Error: sns_scp_simple_rw failed  1020  sns_flight_controller_sensor_
```
Additionally the command will fail after many of these errors and then I will get BARO 0 timeout fails that I don't normally see, which I think is the result of clobbering the onboard baro.

Any tips for dsp i2c driver development would be helpful, especially trying to figure out why when instantiating a bus it times out. I am basing the driver off of the "tf02pro" that is in voxl-px4 currently and then configuring voxl2-slpi default.px4board to include the driver.

## Reply by Eric Katzfey (ModalAI staff) · 2024-01-18 20:37:16 UTC

@brahim Is the code public? Can I take a look?

## Reply by brahim · 2024-01-18 22:37:29 UTC

Hey Eric, so I ruled out the dsp as the problem since I am getting the same behavior on an nxp nuttx-flashed board. It appears the external device is the issue as it is not responding to i2c commands. From what I can tell qurt uses the same I2C 'transfer' command at least with the same parameters. It can find the device on the bus when I give the command "qshell xm125_evk start -X -b 4" but probing it appears to be impossible right now.