sps30_stop_measurement issuing the wrong command

[utilebit]

First, thank you for providing this driver and implementation for the SPS30.

When the sps30_stop_measurement method in the sps30.c is called the SPS30 sensor's fan still runs and does not return to idle.

s16 sps30_stop_measurement() {
    u8 param_buf[] = SPS_SUBCMD_MEASUREMENT_STOP;

    return sensirion_shdlc_tx(SPS_ADDR, SPS_CMD_MEASUREMENT,
                              sizeof(param_buf), param_buf);
}

The sps30_stop_measurement method shown above sends a length of 1 and the stop command 0x00 as a sub-command to the sensirion_shdlc_tx method. The SPS30 datasheet for the stop command provides the following example frame for the stop command:

0x7E 0x00 0x01 0x00 0xFE 0x7E

This example frame uses the command 0x01 instead of 0x00 and since it does not have sub-commands it uses a length of zero. The current method does not send the example frame for MOSI described in the datasheet. For this reason, I believe this is a bug.

I was able to fix the bug by adding the constant:

#define SPS_CMD_STOP_MEASUREMENT 0x01

and modifying the method to be:

s16 sps30_stop_measurement() {
    return sensirion_shdlc_tx(SPS_ADDR, SPS_CMD_STOP_MEASUREMENT, 0, NULL);
}

[abrauchli]

Hi @utilebit, many thanks for the detailed report and the proposed fix. Would you like to submit a pull request or are you happy with leaving it to us?

When submitting a patch, consider that SPS_CMD_MEASUREMENT would also better be renamed to SPS_CMD_START_MEASUREMENT.

[utilebit]

You are welcome @abrauchli . I submitted a pull request with the fix and the renamed constant.

[abrauchli]

Thanks, merged as 6e3256e (#23)