DLPU082C August 2021 – March 2024 DLPC7540
The Response packet is the format in which the DLP Controller replies to the host. The Response packet format is followed for both Write Response and Read Responses. For write commands, the Response packet is sent only if the "reply requested" bit is set in the command header.
The DLP Controller matches the response header to the same format as the incoming Command packet header. There is however an exception - if the Response packet is for a command that expects variable number of data bytes, the Response packet includes the length field (irrespective of whether the command packet had length mentioned or not). Also see Section 18.6 related to variable sized commands.
Similar to the definition of Command packet, fields in bold represents fields that are always present.
| Field | Size (bytes) | Description |
|---|---|---|
| Header | 1 | See Table 18-4 |
| Length | 2 or 0 (Optional as per Datalength Present field in the header) | Length of the command data in bytes following this byte. Checksum is not included in length. For example, length=10 means there are 10 bytes of data after this length field. The LSB of length is sent first followed by the MSB. |
| Data | 0-511 (total of max 512 bytes in the whole message including header and checksum) |
Response data bytes depends on the command code. If error bit in the header is set, there is one data byte. This byte indicates the error code that caused the command to nack. The error code definitions are listed in Table 18-5. |
| Checksum |
1 or 0 (optional as per Checksum present field of header byte) |
Checksum of all bytes in the message including header bytes. Fletcher's checksum. |
| Bits | Field Name | Values |
|---|---|---|
| 0:2 | Destination | See Section 18.3 |
| 3 | Reserved | NA |
| 4 | Datalength Present | 1 = Length field present in the extended header 0 = No length field |
| 5 | Checksum Present | 1 = Checksum present after data bytes 0 = Checksum not present |
| 6 | Error | 1 = Error. First data byte will have the error code that gives more information about the failure 0 = No error |
| 7 | Busy | 1=system busy/response not ready; 0=response ready. Applicable only for I2C based communication |
| Error Code | Description |
|---|---|
| 1 | Invalid destination |
| 2 | Invalid or unknown command |
| 3 | Invalid length |
| 4 | Allocated buffer is not enough to store a command |
| 5 | Length information missing for a variable sized command |
| 6 | Checksum mismatch |
| 7 | Controller not compatible to run the application |
| 8 | Read not supported |
| 9 | Write not supported |
| 10 | Execution failed |
| 11 | Invalid response length |
| 12 | Buffer full |
Write responses are optional as described in the command header description above. If response is requested, it is imperative to read the response (both Write Response and Read Response) immediately following the respective Command Packet. The response of a command is lost as soon as the DLP Controller receives another set of bytes from the host.