BME280: Reading Temperature Skipped

[ttuser]

Hello,

I have a BME280 device and read the data out with the Linux kernel module bmp280-i2c. From time to time, I get the message "reading temperature skipped", i.e. the device sends the value 0x80000. It happens irregularly. If it happens, this error arises several times within a period of some seconds, then it takes few hours until the error comes next time.

In the data sheet it is written that temperature read out can be skipped by setting the oversampling ratio to zero and then the device sends the 0x80000 value. My oversampling ratio for the temperature is 16 and I don't change it at all. I have checked that the oversampling ratio is not zero when the 0x80000 value is sent.

What are possible reasons that the device sends this value?

[FAE_CA1]

Hi,

Thank you. Please send a private message to me with your company email address. I will introduce you to our local FAE for further support.

Thanks.

[yanboss]

Hi,

I have the exact same issue. What was the solution?

It is not clear from the data sheet if:

1. a value of 0x800000 always means the reading was skipped (as the kernel driver assumes)
2. is a valid reading if the measurement is not being skipped and is the value read if it is being skipped
   
   

Could you confirm which answer is correct so I can either fix the kernel driver or need further support to understand why readings are being skipped.

I am based in the UK

Thanks

[FAE_CA1]

Hi,

If the sensor is continuously running in normal mode, 'skipped values' (0x80000) should not be observed in the data registers anymore as soon as one conversion was successfully completed, since the previous value with remained cached if the register is over-read.

In my opinion, the most probable root causes for the behavior on the log could be that:

• The OS/driver triggers configuration updates/changes to the sensor. If the sensor is at least temporarily switched to sleep mode, or the ‘osrs_t’ (temperature oversampling) settings is temporarily set to ‘0’, then the temperature ADC register will be reset to 'skipped values' (0x80000) until the first measurement/conversion cycle is completed,
• The OS/driver triggers a hard- or soft-reset of the sensor from time to time. Again here booting from sleep mode would reset the temperature ADC registers to 0x80000 until the first conversion is completed.

Please let us know how it goes.

Thanks.

[yanboss]

Thanks for your reply.

Can Iconfirm you are saying it is not possible for the BME280 to read 0x800000 for temperature if the temperature has been successfully read by the chip? Even if the temperature current temperature would give this value?

Looking at a log of the data on the I2C bus neither of your suggestions seem to fit the data I have recorded. The BME280 is always on in our design so is only hard reset on a system power cycle. In the log below from you can see a successful read of 0x77FF10, followed by the "skipped" value of 0x800000 1 second later with several retries as this value is currently considered bad. Then finally 1 second later a successful read of 0x800050.

To me this looks like option 2 of the data sheet interpretations I gave above with the value of 0x800000 being valid (it corresponds to a temperature of 23.34 C using the  compenstation formulat in the linux driver).

The ctrl_meas register (0xF4) is set to 0x57 when the driver first loads. This corresponds to osrs_t = 010 2x oversampling and osrs_p = 101 16x oversampling, normal mode.
The config register is set once to 0x08, t_standby 0.5ms, filter coefficient 4 

Time [s]	Decoded Protocol Result
-1.00761985	Setup Write to [0x77] + ACK
-1.00697025	0xFA + ACK
-1.0062784	Setup Read to [0x77] + ACK
-1.0056269	0x7F + ACK
-1.0049568	0xFF + ACK
-1.00480575	0x10 + NAK
-1.00446535	Setup Write to [0x77] + ACK
-1.0043149	0xFD + ACK
-1.0041434	Setup Read to [0x77] + ACK
-1.0039917	0x65 + ACK
-1.00384005	0x7D + NAK
-1.0034806	Setup Write to [0x77] + ACK
-1.0033302	0xFA + ACK
-1.0031587	Setup Read to [0x77] + ACK
-1.00300765	0x7F + ACK
-1.0028579	0xFF + ACK
-1.0027075	0x10 + NAK
-1.0023701	Setup Write to [0x77] + ACK
-1.0022197	0xF7 + ACK
-1.00204815	Setup Read to [0x77] + ACK
-1.0018965	0x4F + ACK
-1.0016949	0x3A + ACK
-1.00154255	0xF0 + NAK
-0.00679885	Setup Write to [0x77] + ACK
-0.00664845	0xFA + ACK
-0.00647755	Setup Read to [0x77] + ACK
-0.0063265	0x80 + ACK
-0.00617675	0x00 + ACK
-0.00602635	0x00 + NAK
0.00160155	Setup Write to [0x77] + ACK
0.0017801	0xFA + ACK
0.00200155	Setup Read to [0x77] + ACK
0.00215515	0x80 + ACK
0.0023081	0x00 + ACK
0.00245915	0x00 + NAK
0.0109354	Setup Write to [0x77] + ACK
0.0111037	0xFA + ACK
0.0112317	Setup Read to [0x77] + ACK
0.01133475	0x80 + ACK
0.0114365	0x00 + ACK
0.01153825	0x00 + NAK
0.01936935	Setup Write to [0x77] + ACK
0.01952745	0xFA + ACK
0.01970025	Setup Read to [0x77] + ACK
0.0198519	0x80 + ACK
0.0200017	0x00 + ACK
0.02015785	0x00 + NAK
0.9924992	Setup Write to [0x77] + ACK
0.9926016	0xFA + ACK
0.99272385	Setup Read to [0x77] + ACK
0.9928256	0x80 + ACK
0.9929261	0x00 + ACK
0.99302785	0x50 + NAK
0.993318	Setup Write to [0x77] + ACK
0.9934198	0xFD + ACK
0.99354265	Setup Read to [0x77] + ACK
0.9936444	0x65 + ACK
0.9937462	0x70 + NAK
0.99405475	Setup Write to [0x77] + ACK
0.9941565	0xFA + ACK
0.99427875	Setup Read to [0x77] + ACK
0.9943805	0x80 + ACK
0.99448165	0x00 + ACK
0.9945834	0x50 + NAK
0.9948706	Setup Write to [0x77] + ACK
0.99497235	0xF7 + ACK
0.9950946	Setup Read to [0x77] + ACK
0.99519635	0x4F + ACK
0.99529745	0x3A + ACK
0.9953992	0xC0 + NAK

[FAE_CA1 · Accepted solution]

Hi,

Please try the attached "bme280_v1.3.1_Linux_driver.zip" to see if the issue can be resolved or not.

Thanks.