nrf52832 - TWIM vs TWI - Transfer with long FIFOs

[akshaymishra]

Hello,

        I am using the nRF52832 in a design where I have to read long buffer (>255 bytes). Using "nrfx_twim_rx" keeps things reliable however with nrfx_twi_rx the transfer becomes inconsistent. I am unable to read beyond a couple of bytes.

The return code is successful so have been unable to diagnose the reason.

Please advise on the probable configuration differences to enable this.

Thanks,

[awneil]

have you used a scope or analyser to check what's happening on the wires?

[akshaymishra]

When using nrfx_twim_rx -- I can read upto 255 bytes without any issue.

When using nrfx_twi_rx -- the clock is visible for the duration but the data is not captured. No change in hardware/ settings.

I am attempting the nrfx_twi_rx since I assume I will be able to eventually read >255 bytes in 1-trasaction.

thanks,

[awneil]

akshaymishra said:

the data is not captured

not sure what you mean by that?

• the Slave is transmitting correctly on SDA, but your software is not seeing that data?
• there is no activity on SDA?
• other ... ?

[akshaymishra]

The slave is transmitted transmitting correctly. With twim reads the data is latched correct but with twi reads the only first few bytes (8-12) bytes get captured. the SDA line shows valid data.

Edit: grammar

[Kenneth]

The TWIM on nRF52832 only support 255bytes (8-bit), ref MAXCNT register:
https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52832.ps.v1.1/twim.html#register.RXD.MAXCNT

So if you set a value larger than 255bytes, it likely will likely mask bits that are >8-bit, thereby only a few bytes are read. 

The actual MAXCNT are different between nRF52 variants, see here:
https://devzone.nordicsemi.com/f/nordic-q-a/50513/twi-maximum-data-transfer-size-in-nrf52832/202150#202150 

However the twi driver should not have such limitation, since each byte will then be handled in interrupt mode. Though the twi driver was made back in the days when 8-bit was what was sufficient, so maybe there is something leftover 8-bit that prevent this to work as intended.

"When using nrfx_twi_rx -- the clock is visible for the duration but the data is not captured." 

Does it works when <255bytes? 

I could find this case that maybe is related:
https://devzone.nordicsemi.com/f/nordic-q-a/33996/twi-sending-wrong-data---sdk15 

Maybe check the buffers are static.

Kenneth

[akshaymishra]

I am, as yet, verifying my twi attempts with less than 255 bytes which does not seem to succeed. Have not attempted >255 bytes - not knowing what else it'll throw at me.