jwang12340 opened a new pull request, #18039:
URL: https://github.com/apache/nuttx/pull/18039
## Summary
This comprehensive pull request introduces a complete enhancement to the CTU
CAN FD QEMU charcan driver through 6 sequential commits. The changes include:
1. **Bug fix**: CAN FD frame format flag inheritance
2. **Reliability improvement**: Complete TXMB status checking during
interrupt handling
3. **Foundation feature**: Register modification utility function (modreg)
4. **New functionality**: Transmit completion confirmation mechanism
5. **New functionality**: CAN message cancellation support
6. **New functionality**: Complete IOCTL interface for driver state control
## Background and Rationale
### Why These Changes Are Needed
The CTU CAN FD QEMU driver previously had several limitations:
1. **FDF Flag Issue**: When transmitting CAN FD frames, the driver hardcoded
FDF=0, making all frames appear as standard CAN format to the hardware,
preventing proper CAN FD feature utilization.
2. **Incomplete Interrupt Handling**: The interrupt handler could miss
completion events from some of the 4 available transmit mailboxes, potentially
causing transmission delays or hangs during high-frequency operations.
3. **Missing Register Operations**: There was no utility function for atomic
register bit modification, leading to code duplication and potential race
conditions in register operations.
4. **No Transmit Confirmation**: Applications had no standardized way to
know when their sent frames were successfully completed, limiting use in
real-time systems that need precise transmit acknowledgment.
5. **No Message Cancellation**: Once a frame was queued for transmission,
there was no way to cancel it, even before transmission started. This is
critical for real-time control systems that need to abort outdated commands.
6. **Limited Driver Control**: Applications lacked a standard interface to
control driver state (start/stop), recover from error conditions (BUS-OFF), or
manage transmit buffering.
## Impact
qemu ctu canfd charcan driver
## Testing
Test Environment: QEMU ARM v8-R (32-bit, Aarch32)
### Example Test Code
```c
#include <stdio.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <nuttx/can.h>
int main(void)
{
int fd = open("/dev/can0", O_RDWR);
unsigned long state;
struct can_msg_s msg;
printf("=== CTU CAN FD Driver Comprehensive Test ===\n\n");
// Test 1: Get state
ioctl(fd, CANIOC_GET_STATE, &state);
printf("Initial state: %lu\n", state);
// Test 2: Enable driver
state = CAN_STATE_START;
ioctl(fd, CANIOC_SET_STATE, state);
printf("Driver enabled\n");
// Test 3: Send CAN FD frame
msg.cm_hdr.ch_id = 0x123;
msg.cm_hdr.ch_dlc = 8;
msg.cm_hdr.ch_flags = CAN_FDF_FLAG;
memcpy(msg.cm_data, "FD_FRAME", 8);
write(fd, &msg, sizeof(msg));
printf("CAN FD frame sent\n");
// Test 4: Flush transmit buffer
ioctl(fd, CANIOC_OFLUSH, 0);
printf("Transmit buffer flushed\n");
// Test 5: Disable driver
state = CAN_STATE_STOP;
ioctl(fd, CANIOC_SET_STATE, state);
printf("Driver disabled\n");
close(fd);
printf("=== All tests completed successfully ===\n");
return 0;
}
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