TWI is not working with SoftDevice

[diode]

This seems to be a common problem after searching in this forum. In my case, I need to read from an I2C slave and send the data out in BLE. I have made it work without SoftDevice using this library code http://pastebin.com/qLLAy418 . However, it failed to work with SoftDevice. I also tried with another version which has SoftDevice knobs http://pastebin.com/AV6cQK0x. It doesn't work either. I also tried other code github.com/.../twi_hw_master.c that someone claimed to work (devzone.nordicsemi.com/.../), but it doesn't work for me. Can anyone provide any suggestion on this problem?

[RK]

What does 'doesn't work' mean? Crashes, sends erratically, goes to the hardfault handler, the board bursts into flames, what?

The TWI handler in the library works with the softdevice quite happily, as it should, they are entirely separate things.

So what exactly happens when you use the nordic TWI driver from the SDK for your board with and without the softdevice?

[RK]

I can't make any sense of that logic analyser trace at all. For a start the trace marked data is way too regular, that looks like a clock, and the other one never changes, if it was data it would at least have to go low at some point for a start bit. And if anything was clock stretching the clock line would stay low, not high.

I think you need to start over and capture a full trace without the softdevice and a full trace with it and see if/where they start to differ. If it works without the softdevice I'd start putting in some delays in the code to simulate the times the softdevice is busy during which the TWI should be in SUSPEND mode (holding SCL low) until the byte is read and it's RESUMEd at which point it should read the next one. That should tell you if the peripheral you're trying to read from is doing the right thing. TWI is a hardware peripheral, SD should make no difference.