35.6.3.9.2 Pointer Operation in Client Mode

In Client mode, the transmit / receive sequence is started by the SPI receiving an SCK clock pulse. As soon as an SCK pulse is received, the SPI transmits the data pointed to by the SPIRDPTR. When a complete data is shifted in, the SPIRDPTR / SPIWRPTR are incremented, another data are shifted in/out, and so on. The newly received data is written to the RX FIFO location pointed to by SPIWRPTR. The CPUWRPTR is incremented by one every time the CPU writes a new data to the TX FIFO memory array. If the CPUWRPTR is pointing to location n, and SPIWRPTR is pointing to location n, and a wrap is not detected, the CPUWRPTR will auto-increment to SPIWRPTR, to keep up with SPIWRPTR. This is so that the next data to be transmitted will be placed in the correct position in the storage element. The CPU can read data from RX FIFO as long as FIFOSPACE.RXSPACE != 0. When both RX shifter and RX FIFO are full, the Buffer Overflow status bit is set (STATUS.BUFOVF) and optional ERROR interrupt is generated. The module will not respond to SCK transitions while BUFOVF is ‘1’, effectively disabling the module until software reads RX FIFO. All pointers increment to their maximum value, dictated by CTRLC.DATA32B bit, and then roll over to ‘0’. CPURDPTR will not increment past SPIWRPTR. In other words, if CPURDPTR = SPIWRPTR, and the CPU attempts another read, the pointer will stay at the value of SPIWRPTR.