nrf_twi_mngr handling of transfers larger than 255 Bytes

[raemond]

I am trying to send more than 255 Bytes of data over I2C so I break it up into 255 byte transfers within a transaction.

I notice a stop/start condition is sent between I2C transfers even if I use the NRF_TWI_MNGR_NO_STOP flag for each transfer.

This seems to contrary to the comment at line 74 in nrf_twi_mngr.c:

/* If it is possible try to bind two transfers together. They can be combined if:
     * - there is no stop condition after current transfer.
     * - current transfer is TX.
     * - there is at least one more transfer in the transaction.
     * - address of next transfer is the same as current transfer.

*/

Is there a way to accomplish this?

[Jakub Rzeszutko]

Hi,

1. What SDK are you using?

2. What uC are you using?

3. Do you use I2C with EasyDMA support?

[raemond]

1. SDK 15.0.0

2. nRF52840

3. EasyDMA is enabled for the interface.

[raemond]

It seems to happen whether or not EasyDMA is enabled.

[jakub]

I think I know what the problem is, twi_mngr is using legacy driver. Legacy driver has hard coded limitation set on transmit buffers to 8bits.

One needs to migrate twi_mngr to use nrfx driver and the problem will be solved. Nrfx driver is capable to use tx buffer according to used SoC:

•  8   bit for nrf52832
• 10 bit for nrf52810
• 16 bit for nrf52840

[raemond]

I noticed the limitation on the length set by the usage of a uint8_t buffer length variable. So that's why I broke it up into pieces. Comments with the twi_mngr indicated that they would be grouped if I used the NRF_TWI_MNGR_NO_STOP flag, but that doesn't appear to be the case.