38.6.5.4 Debug on CAN Support
Debug messages are stored into Rx Buffers. For debug handling three consecutive Rx buffers (e.g. #61, #62, #63) have to be used for storage of debug messages A, B, and C. The format is the same as for an Rx Buffer or an Rx FIFO element (see 38.7.2 Rx Buffer and FIFO Element ).
Advantage: Fixed start address for the DMA transfers (relative to RXBC.RBSA), no additional configuration required.
For filtering of debug messages Standard / Extended Filter Elements with SFEC / EFEC = “111” have to be set up. Messages matching these filter elements are stored into the Rx Buffers addressed by SFID2 / EFID2[5:0].
After message C has been stored, the DMA request output is activated and the three messages can be read from the Message RAM under DMA control. The RAM words holding the debug messages will not be changed by the CAN while DMA request is activated. The behavior is similar to that of an Rx Buffers with its New Data flag set.
After the DMA has completed the DMA unit sets the DMA acknowledge. This resets DMA request. Now the CAN is prepared to receive the next set of debug messages.
Filtering for Debug Messages
Filtering for debug messages is done by configuring one Standard / Extended Message ID Filter Element for each of the three debug messages. To enable a filter element to filter for debug messages SFEC / EFEC has to be programmed to “111”. In this case fields SFID1 / SFID2 and EFID1 / EFID2 have a different meaning (see 38.7.5 Standard Message ID Filter Element and 38.7.6 Extended Message ID Filter Element). While SFID2 / EFID2[10:9] controls the debug message handling state machine, SFID2 / EFID2[5:0] controls the location for storage of a received debug message.
When a debug message is stored, neither the respective New Data flag nor IR.DRX are set. The reception of debug messages can be monitored via RXF1S.DMS.
| Filter Element | SFID1[10:0] / EFID1[28:0] | SFID2[10:9] / EFID2[10:9] | SFID2[5:0] / EFID2[5:0] |
|---|---|---|---|
| 0 | ID debug message A | 01 | 11 1101 |
| 1 | ID debug message B | 10 | 11 1110 |
| 2 | ID debug message C | 11 | 11 1111 |
Debug Message Handling
The debug message handling state machine assures that debug messages are stored to three consecutive Rx Buffers in correct order. In case of missing messages the process is restarted. The DMA request is activated only when all three debug messages A, B, C have been received in correct order.
