Cynerd opened a new pull request, #17283:
URL: https://github.com/apache/nuttx/pull/17283
## Summary
This adds ioctl to NuttX's CAN that allows control of the read behavior.
## Impact
The old behavior of reading multiple frames with a single read is preserved.
The new ioctl just adds the ability to limit it. That includes not only
disabilities but also more versatile limitations based on the size, which
allows for multiple frames to be read.
## Testing
Tested on a custom SAMv7 board.
```c
int fd = open("/dev/can0", O_RDWR);
if (fd < 0) {
syslog(LOG_ERR, "Failed to open can: %s", strerror(errno));
return -1;
}
size_t iw = SIZE_MAX;
ioctl(fd, CANIOC_SET_IWATERMARK, &iw);
while (true) {
sleep(1); /* Give us some time to use cansend multiple times*/
struct can_msg_s frame;
size_t n = read(fd, &frame, sizeof frame);
syslog(LOG_INFO, "Read %d id%d", n, frame.cm_hdr.ch_id);
}
```
```
for i in {0..4}; do cansend can0 "00$i##0"; done
```
For `iw == SIZE_MAX`:
```
[1762352028.612600] startup_main: Read 4 id0
[1762352029.613000] startup_main: Read 16 id1
```
for `iw == 0`:
```
[1762352153.185100] startup_main: Read 4 id0
[1762352154.185500] startup_main: Read 4 id1
[1762352155.185900] startup_main: Read 4 id2
[1762352156.186300] startup_main: Read 4 id3
[1762352157.186700] startup_main: Read 4 id4
```
for `iw == 5`:
```
[1762352293.124000] startup_main: Read 4 id0
[1762352294.124400] startup_main: Read 8 id1
[1762352295.124900] startup_main: Read 8 id3
```
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