It turned out to be trying to read from wrong Serial port.
Reading from /dev/ttyS3 worked.
I later realize that serial port are from /dev/ttyS0 .. /dev/ttyS9
Pergunta
I am trying to write a c program to read data for morningstar sunsaver MPPT.
This is the simple program I found in net. But my program is unable to read data from register.
#include <stdlib.h>
#include <errno.h>
#include "src/modbus.h"
int main(void)
{
modbus_t *ctx;
uint16_t tab_reg[64];
int rc;
int i;
ctx = modbus_new_rtu("/dev/ttyS0", 115200, 'N',8,1);
if (ctx == NULL) {
fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));
modbus_free(ctx);
return -1;
}
rc = modbus_read_registers(ctx, 0, 10, tab_reg);
if (rc == -1) {
fprintf(stderr, "%s\n", modbus_strerror(errno));
return -1;
}
for (i=0; i < rc; i++) {
printf("reg[%d]=%d (0x%X)\n", i, tab_reg[i], tab_reg[i]);
}
modbus_close(ctx);
modbus_free(ctx);
}
It does not work for me. I get the following error message:
Bad file descriptor
Solução 2
It turned out to be trying to read from wrong Serial port.
Reading from /dev/ttyS3 worked.
I later realize that serial port are from /dev/ttyS0 .. /dev/ttyS9
Outras dicas
By reading the documentation from LibModBus, I think you're missing a call to modbus_connect.
Try connecting before reading registers:
ctx = modbus_new_rtu("/dev/ttyS0", 115200, 'N',8,1);
if (ctx == NULL) {
fprintf(stderr, "Creation failed: %s\n", modbus_strerror(errno));
return -1;
}
if (modbus_connect(ctx) == -1) {
fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno));
modbus_free(ctx);
return -1;
}
Also, remember to modbus_close
and modbus_free
your context before exiting due to further error conditions. For example:
rc = modbus_read_registers(ctx, 0, 10, tab_reg);
if (rc == -1) {
fprintf(stderr, "%s\n", modbus_strerror(errno));
modbus_close(ctx);
modbus_free(ctx);
return -1;
}