How to use EasyDMA when calling nrfx_twim_tx

[Christopher Hunt]

Hi there,

I've got a situation when using TWI where an `NRF_ERROR_INVALID_ADDR` is returned having performed a call to `nrfx_twim_tx`. I understand that this relates to the data to be sent not being in an EasyDMA area of memory. My question is, how do I put data into the correct place? I've gone through the documentation and examples and cannot find any further guidance.

Here's my code thus far:

ret_code_t err_code = nrfx_twim_tx(&m_twim, &i2c_address, &data, sizeof(data), false);

It appears that where the size of the data is greater than 3, I get a NRF_ERROR_INVALID_ADDR in return. Specifically, I'm transferring 28 bytes when I get that error.

Thanks for any help.

Kind regards,
Christopher

[Christopher Hunt]

I think there's something uncanny about looking at something for a number of hours, posting a question, and then seemingly resolving it oneself. :-) In essence, I think the data being referred to in this case is in flash because it is declared as a `const`. I will report back.

[Christopher Hunt]

Yep, that was it. Ensure to not copy from const!

On a slightly related topic, the code I've been given is attempting to transfer a buffer of 2048 bytes... that's not going to work for TWI transfers, right?

[Christopher Hunt]

More info: I’m using the nrf52840. I’m confused as to how many bytes I can actually send in one transmission. Some forum posts are stating 255 bytes, others are stating up to 65535. I’m endeavouring you use the nrfx APIs.  

[Christopher Hunt]

Well... so it seems as though I can transmit 2048 bytes ok after all. The NRF_LOGGER seemed to overflow its own buffer when trying to hexdump print the buffer (I had TWI debug level logging on). The NRF_LOGGER shouldn't attempt to log more characters than that of NRF_LOG_STR_PUSH_BUFFER_SIZE or something, but I think it does. Turning off the debug log got things working.

[Marjeris Romero]

Christopher Hunt said:

’m confused as to how many bytes I can actually send in one transmission. Some forum posts are stating 255 bytes, others are stating up to 65535. I’m endeavouring you use the nrfx APIs.  

 Hi Christopher,

I am sorry your questions haven't been answered earlier, but it looks like you found out about the original problem in your ticket. Regarding how many bytes you can send in one transmission, it will depend on the "EasyDMA MAXCNT bit lenght", see an overview here. For nRF52840 TWI 16 bit lenght field will give you 65535. If you need any more help on this topic please open a new ticket, as I will mark your ticket here as "answered".

Best regards,

Marjeris