How to void repeated TWI start condition using nrf_drv_twi_tx()

RE: How to void repeated TWI start condition using nrf_drv_twi_tx()

awneil — Wed, 10 Mar 2021 10:25:07 GMT

[quote userid="87195" url="~/f/nordic-q-a/72557/how-to-void-repeated-twi-start-condition-using-nrf_drv_twi_tx/298938#298938"] I have to copy up to 500 bytes at a time [/quote]

Check the nrf_drv_twi_tx() documentation: the length parameter is a uint8_t - so you can't do that anyhow.

https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.2/group__nrf__drv__twi.html#ga6c83eac2d358bc8fb5b53c53f22506b6

An nRF52832 has at least 32K RAM - so finding a 256 (or 257?) byte buffer shouldn't be too hard?

[quote userid="87195" url="~/f/nordic-q-a/72557/how-to-void-repeated-twi-start-condition-using-nrf_drv_twi_tx/298938#298938"]What can I do?[/quote]

Again, have you looked at the register level - ie, is this just a software API restriction, or is it an actual hardware limitation?

RE: How to void repeated TWI start condition using nrf_drv_twi_tx()

StefXinet — Wed, 10 Mar 2021 09:42:09 GMT

a big problem caused by having to put the address byte and the data bytes in the same array is that I don't know how to handle transmissions of a lot of data. I have to copy up to 500 bytes at a time and I cannot copy each time to RAM in a new array of 501 bytes, 1 byte of address and 500 bytes of data.

What can I do?

RE: How to void repeated TWI start condition using nrf_drv_twi_tx()

StefXinet — Tue, 09 Mar 2021 16:19:49 GMT

Dear awneil,

having the address and the data in the same array is not convenient because in this way the function nrf_drv_twi_tx() that has the same name in SDK 17 and SDK11 accepts the same parameters but produces two different outputs (I checked with the oscilloscope).
The only workaround seems to be to copy each time the address plus all the data in a single array and call the function function nrf_drv_twi_tx(), in this way it wastes time, and also RAM is wasted

RE: How to void repeated TWI start condition using nrf_drv_twi_tx()

awneil — Tue, 09 Mar 2021 16:14:36 GMT

[quote userid="87195" url="~/f/nordic-q-a/72557/how-to-void-repeated-twi-start-condition-using-nrf_drv_twi_tx/298726#298726"]is there a way to get the code to work without putting both the address and the data in the same array[/quote]

What's the problem with having them in the same array?

It doesn't look like the API supports it - dunno if you could do it with direct register access?

RE: How to void repeated TWI start condition using nrf_drv_twi_tx()

StefXinet — Tue, 09 Mar 2021 13:42:45 GMT

Yes, this could be a tricky workaround.

Im also using older SDK (ver 11) for nRF51 and for nRF51 there is no start repeated condition and no slave address repeated send.

So is there a way to get the code to work without putting both the address and the data in the same array?

RE: How to void repeated TWI start condition using nrf_drv_twi_tx()

awneil — Tue, 09 Mar 2021 13:21:02 GMT

[quote userid="87195" url="~/f/nordic-q-a/72557/how-to-void-repeated-twi-start-condition-using-nrf_drv_twi_tx"]the problem I have is that the start condition and the slave address are sent twice[/quote]

that's because you do two separate I2C transactions. You need to do them as just one - make the 'Word Address' the first byte of the buffer that you send:

p_buff[0] = word_address;
p_buff[1] = data_byte_1;
p_buff[2] = data_byte_2;

err_code = nrf_drv_twi_tx( &twi_instance, 0x50, p_buff, 3, false );