Incrementing the TX buffer in PPI-driven SPI

RE: Incrementing the TX buffer in PPI-driven SPI

user113706 — Mon, 30 May 2022 11:08:03 GMT

Sorry for the late reply.

I am currently on another task and will try the method you advised once that is complete.

RE: Incrementing the TX buffer in PPI-driven SPI

user2111 — Tue, 24 May 2022 07:55:17 GMT

So you need to for intance set SPIM.TXD_MAXCNT and SPIM.TXD_PTR like any SPIM transfer, however if you also enable SPIM.TXD_LIST, then for each 'n' SPIM transfer that you call SPIM.TASKS_START then the TXD_PTR will point to the memory address TXD_PTR+MACNT*'n'.

So that is why you need to define for instance:

#define BUFFER_SIZE 2

typedef struct ArrayList
{
uint8_t buffer[BUFFER_SIZE];
} ArrayList_type;

ArrayList_type TXDList[10] ;

NRF_SPIM->TXD.MAXCNT = BUFFER_SIZE;
NRF_SPIM->TXD.PTR = &TXDList;
NRF_SPIM->TXD.LIST = 1;

You may also need to do the same for RXD buffer if you want it to increment the same way.

If you want to start from the beginning of the ArraList again then you need to write one time to NRF_SPIM->TXD.PTR before calling start task again.

Best regards,
Kenneth

RE: Incrementing the TX buffer in PPI-driven SPI

user113706 — Tue, 24 May 2022 04:34:10 GMT

Reply, thanks.

https://infocenter.nordicsemi.com/topic/ps_nrf52840/easydma.html#arraylist
in the EasyDMA array list for examples and Figure 3.
So the questions are.

(1) ’Then each start task will increment the buffer pointer:’
What is a pointer in this case? Does the pointer here mean READER.PTR = &ReaderList = 0x20000000?

(2) Read order
In this example, does this mean that the address to be read is incremented as follows?
RaderList[0]-buffer[0]--->RaderList[0]-buffer[1]--->RaderList[0]-buffer[2]--->RaderList[0]-buffer[3]--->RaderList[1]-buffer[0]--->RaderList[1]-buffer[1]--->--->--->--->--->--->--->--->--->--->--->----->--->--->--->--->--->--->--->--->--->RaderList[2]-buffer[2]--->RaderList[2]-buffer[3].

(3) 'Then you need to update the buffer array and set the pointer to the start of the buffer array again.'
The following is a list of the Specifically.
--RaderList[0]-buffer[0] to RaderList[2]-buffer[3] then you need to update the contents of the buffer array.
--READER.PTR = &ReaderList = 0x20000000, revert.
Does this mean?

RE: Incrementing the TX buffer in PPI-driven SPI

user2111 — Mon, 23 May 2022 13:49:16 GMT

Sounds to me that you need to look at array list, then each start task will increment the buffer pointer:
https://infocenter.nordicsemi.com/topic/ps_nrf52840/easydma.html#arraylist

Then after executing the start task let's say 10 times, then you need to update the buffer array and set the pointer to the start of the buffer array again.

Alternatively you need to look into giving the spi interrupt priority 0, but that may affect the real-time handling of the ESB protocol in a negative way (e.g. affect ack).

In either case the CPU will need to do some CPU processing before/after e.g. 10 transfers.

Kenneth