how to use nrf52832 twis easyDMA with larger (>255) packetsize?

[Andrej]

Hi,

my current project needs an i2c slave eeprom emulation like it is in the example projects of the sdk. The difference is that I need a larger packagesize of one transmission.

I tried to reload the easyDMA while transmitting without any success. In other questions some users mentioned a list mode function.

Can someone give me an example how to send larger packagesizes?

Best regards

Andrej

[bjorn-spockeli]

The MAXCNT register is 8 bit and the Easy DMA does not support LIST feature for TWIS, so its not possible to send more than 255 bytes per transmission as you have to update the packet pointers manually.

Best regards

Bjørn

[Andrej]

First, thanks for your post. Could you tell me where, when and how i have to update the easyDMA? I tried on the Overread Event to update the pointer but i noticed that it would be one byte to late.

An example would be great.

[bjorn-spockeli]

I am afraid that its not possible to do that with the TWIS of the nRF52. As you stated if your TWI Master performs a sequential read of more than 255 bytes, i.e. sents an ACK after byte 255, then you'll get OVERREAD event when it tries to read the 256th byte and at this point its to late to update the EasyDMA TXD.PTR pointer. If we had implemented the TWIS in such a way that you got an event when there was 1 byte left in the TX buffer, then it would have been possible stretch the clock and update the TXD.PTR.