38.5.4.2 Memory to Peripheral Transfer

XDMAC reads data from source memory location and writes to the destination peripheral.

Memory to Peripheral transfer is also a peripheral synchronized transfer. It has totally four levels of data transactions. They are Host, Block, Microblock, and Chunk level transactions. Host, Block, and Microblock level transactions work exactly the same way as explained earlier in the memory to memory data transfer section. In memory to peripheral data transfer, the burst level transaction is not present. The microblock is directly split into chunk level data transaction.

XDMAC Chunk and Incomplete Chunk: When a memory to peripheral transfer is activated, the microblock level transaction is directly split into a number of data chunks. The chunk size is configured in CSIZE field of XDMAC Channel Configuration Register (XDMAC_CCx). The chunk size denotes the number of ‘data’ to be transferred from memory to the corresponding peripheral transmit register. In general, the chunk size is set as ‘1 data’ in most of the peripherals (example: - UART, SPI, TWI, etc.), as the maximum size of their transmit register is ‘1 data’. In specific scenarios, the chunk size is chosen more than 1 data. For example, the data transmit/output registers of AES and HSMCI modules can hold more than ‘1 data’. So, the chunk size can be chosen as '2/4/8/16 data' accordingly. In this case, the larger the chunk size is, the better the performance is. During ‘memory to peripheral’ transfer, the data chunks are immediately transferred when there is a hardware/software trigger. Memory burst size doesn't play any role here. When the microblock size is not a multiple of the chunk size, the last chunk being transferred contains the last trailing data.