SPRUIU1D July 2020 – December 2024 DRA821U , DRA821U-Q1
The XMODEM protocol is used to transfer boot data. Only CRC mode is supported (not checksum), with both 128- and 1024-byte block sizes. The general, format of received frames is shown in Table 4-70 and Table 4-71.
| STX | Block Num | Inv Block Num | 1024 data bytes | CRC | CRC | |||
| SOH | Block Num | Inv Block Num | 128 data bytes | CRC | CRC | |||
| Field | Value | Description |
|---|---|---|
| STX | 0x02 | The start character for 1024-byte CRC data blocks |
| SOH | 0x01 | The start character for 128-byte CRC data block |
| Block Num | 0x01-0xFF – 0x00 | The block number. The first block has value 1, and the block number wraps around 0xFF to 0 |
| Inv Block Num | 0xFE-0x00 | The inverse block number (bit inverse of the block number) |
| CRC | Calculated | The 16-bit CRC generated from the polynomial 0x1021 |
The XMODEM protocol is implemented as a half-duplex protocol as shown in Table 4-72.
| Transmitter Sends | Receiver Sends | |
|---|---|---|
| ← | Ping (‘C’) | |
| Frame 1 | → | |
| ← | ACK (or NACK) | |
| Frame 2 | → | |
| ← | ACK (or NACK) | |
| EOT | → | |
| ← | ACK (or NACK) |