14.1.3 Data Packet Format

The Data Packet Format is used in either direction (Host to Client or Client to Host) to transfer opaque data. A command frame is used either to inform the Client that a data packet is about to be sent or to request the Client to send a data packet to the Host. In the case of Host to Client, the Client sends a response after the command and each subsequent data frame. The format of a data packet is shown below.

To support DMA hardware, a large data transfer may be fragmented into multiple smaller Data Packets. This is controlled by the value of DATA_PACKET_SIZE which is agreed between the Host and the Client in software and is a fixed value such as 256B, 512B, 1KB (default), 2KB, 4KB, or 8KB. If a transfer has a length of m, which exceeds DATA_PACKET_SIZE, the sender must split it into multiple DATA_PACKET_SIZE as shown in Equation 1:

(m – (n-1)* DATA_PACKET_SIZE) -------------------------- Equation 1

Where,

1.. n-1 = length of the DATA_PACKET_SIZE

n = frame length

This is illustrated below.

• If DMA count <= DATA_PACKET_SIZE:

  The data packet is “DATA_Header + DMA count +optional CRC16“, that is no padding.

  

• If DMA count > DATA_PACKET_SIZE:

  

• If remaining data < DATA_PACKET_SIZE, the last data packet is:

  “DATA_Header + remaining data + optional CRC16 “, that is no padding.