How to use select() on default uart console for timeout on blocking read
Posted: Sat Oct 04, 2025 11:58 pm
Hi all. I have a custom `console_get()` function I use to implement a blocking read operation with a timeout. This implementation allows me to use the REPL loop to, for example, interact with the watchdog.
I had this working well on an ESP32-S3, but currently working on an ESP32 it is not working. The console is different on the ESP32, using the default UART setup. I have studied the UART select example but don't see where I might have gone wrong.
The code is below - it should work. I assume the problem is the interaction between VFS and the uart. I use the same console initialization used in the advanced console example. I don't use linenoise. Perhaps the UART has a hardware buffer that cannot be used with select?
I appreciate your help.
I had this working well on an ESP32-S3, but currently working on an ESP32 it is not working. The console is different on the ESP32, using the default UART setup. I have studied the UART select example but don't see where I might have gone wrong.
The code is below - it should work. I assume the problem is the interaction between VFS and the uart. I use the same console initialization used in the advanced console example. I don't use linenoise. Perhaps the UART has a hardware buffer that cannot be used with select?
I appreciate your help.
Code: Select all
int console_get(const char **p_line) {
fd_set readfds;
struct timeval tv;
int rval = ESP_OK;
int time_count = 0;
static char c = 0;
if (c=='\n') { // reset line buffer
buffer_ix = 0;
c = 0;
}
while ((time_count<timeout) && (c!='\n')) {
FD_ZERO(&readfds);
FD_SET(fd_in, &readfds);
tv.tv_sec = 1; // 1 sec timeout
tv.tv_usec = 0;
int result = select(fd_in+1, &readfds, NULL, NULL, &tv);
if (result == -1) {
rval = -1; // note that this will only be returned on the last cycle
} else if (result) { // data
result = read( fd_in, &c, 1);
if (result<=0) {
rval = -2; // should not happen
}
else {
if ((c=='\n') || (c=='\r')) { // done
rval = buffer_ix; // string size
buffer[buffer_ix] = 0;
}
else {
buffer[buffer_ix++] = c;
if ((buffer_ix+1)==BUFFER_SIZE) {
c = '\n'; // clear buffer on next entry
buffer[buffer_ix] = 0;
}
}
}
}
time_count++;
}
if (c=='\n') {
*p_line = buffer;
rval = buffer_ix;
}
return rval;
}