Tricky SPI communication with request and response structure.

[davidmeetsall]

Hi Friends,

I have to implement a request_response function for 8-bit PIC microcontroller. This function has two arguments one is request command structure and other is response structure which is filled after getting response. Its 8-bytes i.e.,

typdef struct{
uint16_t data0;
uint16_t data1;
uint16_t data2;
uint16_t data3;
}data_st;

extern data_st *request;
extern data_st *response;

request_response(&request, &response);

There are 3-4 set of request and response. Which is sent one by one.
When request0 is sent first response must be discarded as there is 8-bytes(64 bits) gap in response from the other system. When request1 is sent response0 is gotten. Same way request2 is sent response1 is received. Same way request..n ...response..n-1 and request_dummy will be sent in the last to receive response..n.

I have to collect the correct response for a request. Means need to map response0 for request0 , response1 for request1 and response2 for request2 for further processing.

How to manage this? Please help.

Thanks,
david.

 

[Okada]

Can't you use sizeof(your struct) and point to to proper location.

 

[alexxx]

If I got this right, then the solution is simple. Create an array of request and responses and call the function as many times as needed. Something like.

extern data_st request[8];
extern data_st response[8];

request_response(&request[0], &response[7]);
request_response(&request[1], &response[0]);
//..................................
request_response(&request[7], &response[6]);

Note that the first call uses response[7], this could be your dummy response for the request 0 case.

 

[ftsolutions]

Can you add another byte or two bytes to the structure and the SPI message?
If you can have multiple requests pending/waiting for a response at a time, just include an incrementing transaction ID number that is set by the Master when the request is done. The response will have to include the same transaction ID # in its response. Or, if your system is not to send another request until the first response is ready to be processed, you could either "poll" the device for a "ready"/complete" status, or you could dedicate an I/O pin on the microcontroller to be activated when a response is ready to be read from the target device.