Version 1100 wrong ERROR_ID read? about ccs811

[maarten-pennings]

Hi @iKlask
You might be right, the buf[5]=0 is fishy.
Do you have a proposed fix?

[dodo041]

Hi @maarten-pennings, I'm working with an adaptation of your code for the CCS811 sensor, written in plain C. Checking the logics, I came across the same issue which was presented by the author. I'm thinking about a fix for the issue, since the else case in line if( ok && stat==CCS811_ERRSTAT_OK ) ok= i2cread(CCS811_ALG_RESULT_DATA,8,buf); else buf[5]=0; definitely seems wrong, since there's no point in overwriting the byte buf[5] containing the error information, when the status byte suggests the existence of an error.

My idea was to read the error id from the error register, when the error bit in the status register is set. So (as before) you read the status register only, check for existing errors, and if the error bit in the status register is set, read the error register e.g. with ok= i2cread(CCS811_ERROR_ID,8,buf); (with CCS811_ERROR_ID being the address 0xE0 in the application register), and then just proccessing the error id as needed.
Afterwards replace the status byte from ALG data with the previously read "correct" status, and if needed the errror id byte with the read error id, otherwise (if there's no error and the error id byte is also errnoeous) set it to 0.

Before going along with this simple fix, I'd like you to supply me with some information (if you still can remember, since the issue is opened for almost 3 years now):

• What was the issue you encountered with the returned status byte, when using firmware version < 2.0.0? @iKlask pointed out, that he did not have problems with versions lower than that.
• Why was it sufficient for you to assume, that there's no error, when
  stat == CCS811_ERRSTAT_OK returned true? If the statement was true, this should only indicate, that 1. the ALG data is ready, 2. the firmware is valid, and 3. the firmware is in application mode: #define CCS811_ERRSTAT_OK (CCS811_ERRSTAT_DATA_READY | CCS811_ERRSTAT_APP_VALID | CCS811_ERRSTAT_FW_MODE)
  An error would only be clearly indicated if the bit at CCS811_ERRSTAT_ERROR is set. In my opinion you wanted to have something like this statement:
  status & CCS811_ERRSTAT_ERROR (or the opposite: we'd have no error when
  status & ~CCS811_ERRSTAT_ERROR returns true)
  Did you even want to check for an existing error, or just for an OK running application?
• In case we indeed look for an error, and the status from CCS811_ALG_RESULT_DATA indeed was wrong, was the error id byte wrong as well? I assume it was, since there would be no point in attempting to set the byte to 0. That would mean, we'd need to update the error byte as described above, but only in case it's wrong just as the status byte is.

Maybe I'm leaving something obvious and important out of my considerations, but for now this seems like the only plausible way of a workaround, if there really were any errors with that firmware versions and the status bytes in ALG data.

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