Inconsistent Error Code in Modbus Client

[aatoof1]

Hi,

In function mbc_validate_wr_response line 230, the return code is ENXIO without the minus sign, is this a bug?

zephyr/subsys/modbus/modbus_client.c

Lines 224 to 234 in 4677920

	switch (fc) {
	case MODBUS_FC05_COIL_WR:
	case MODBUS_FC06_HOLDING_REG_WR:
	case MODBUS_FC15_COILS_WR:
	case MODBUS_FC16_HOLDING_REGS_WR:
	if (req_addr != resp_addr || req_value != resp_value) {
	err = ENXIO;
	} else {
	err = 0;
	}
	break;

In the rest of the code if a positive return code is returned, this indicates a Modbus exception code. See:

zephyr/subsys/modbus/modbus_client.c

Lines 46 to 52 in 4677920

	if (resp_fc & excep_bit) {
	if (excep_code > MODBUS_EXC_NONE) {
	return excep_code;
	}
	return -EIO;
	}

Also in other parts of the code when there is a mismatch between request and response values (i.e function code, unit id) the error code -EIO is returned, with this case being the only exception. See:

zephyr/subsys/modbus/modbus_client.c

Lines 38 to 44 in 4677920

	if (unit_id != ctx->rx_adu.unit_id) {
	return -EIO;
	}
	if (fc != (resp_fc & excep_mask)) {
	return -EIO;
	}

Should ENXIO be changed to -EIO to be consistent with the rest of the Modbus code?

Thanks

[jukkar]

@aatoof1 I think you could send a PR and propose this change, then it gets assigned and reviewed by relevant people.