How to read calibration value of DMP?

[mfide]

How can I read calibration value of DMP and set it back later? Is there an interface for this in the library?

[PaulZC]

Hi Mehmet (@mfide ),

I had a chat with InvenSense about this. They say that it is possible / advisable to store the DMP bias values and restore them after power cycling. The bias values are here. You can read and write them using the readDMPmems and writeDMPmems commands. See here for a write example.

For reading, this should work but is untested:

unsigned char gyroBiasX[4]; // Big-endian
boolean success = (myICM.readDMPmems(GYRO_BIAS_X, 4, &gyroBiasX[0]) == ICM_20948_Stat_Ok); // Read DMP GYRO_BIAS_X register

You will need to reverse the byte order (big-endian to little-endian) if you want to convert gyroBiasX into a int32_t.

Please let me know if this is successful.
Best wishes,
Paul

[mfide]

Thank you Paul for your effort.

When I try to read them like you suggest, gyro bias are changing which is good but the rest of the values I read them as zero.

imu_gyro_bias_x = 19552
imu_gyro_bias_y = 123488
imu_gyro_bias_z = -137536
imu_accel_bias_x = 0
imu_accel_bias_y = 0
imu_accel_bias_z = 0
imu_mag_bias_x = 0
imu_mag_bias_y = 0
imu_mag_bias_z = 0

Is this the case for you as well ?

[PaulZC]

Hi Mehmet,
We are still gaining experience with the DMP and we don't have all the answers...
What happens if you enable the accel, gyro and compass directly?
https://github.com/sparkfun/SparkFun_ICM-20948_ArduinoLibrary/blob/master/examples/Arduino/Example9_DMP_MultipleSensors/Example9_DMP_MultipleSensors.ino#L296-L300
Best wishes,
Paul

[PaulZC]

Hi Mehmet,
Please try the new v1.2.5 of the library. I have made some important changes to the way the magnetometer data is read. Please let me know if the biases are now behaving better.
Best wishes,
Paul

[PaulZC]

Hi Mehmet (@mfide ),
Please take a look at Issue #60 . Ilia found that the bias data does get returned, but only after ~20 seconds or so.
Are you able to confirm this? Do you start to see the bias values if you give the DMP time to internally calibrate?
Best wishes,
Paul

[PaulZC]

Hi Mehmet (@mfide ),

Please try version 1.2.6 of the library. I have made one important change which was preventing the DMP from operating correctly.

I hope this solves your issue. But please re-open this issue if you are still unable to read the bias data, and I will do what I can to help.

Best wishes,
Paul

[mfide]

Hi Paul,

Thank you for the great effort. Today I just tested v1.2.7.
I could read imu_mag_bias_* registers which were coming as zero before.
But imu_accel_bias_* registers are still read as zero.

Mehmet.

[tobiasebsen]

Hi @PaulZC and @mfide

I'm having the same issue. When reading biases, only the Gyro bias reads non-zero values (after ~20 seconds).
Mehmet, how did you get Mag biases?

[Bongasman]

Hi Hi @PaulZC and @mfide, I have also been struggling for some time now to solve the issue of reading the complete 9DoF data, and loading it back on startup. Was anyone able to solve this issue?

[PaulZC]

Hi Bongas (@Bongasman ), Todd and colleagues,

Unfortunately I don't have an answer for you. The DMP is (almost) a complete black box and there are still many things we do not understand about it. I believe it should be possible to read, save and restore the DMP's internal 'calibration' data, and there are methods in the library to let you read and write the DMP registers, but we we have no information or guidance on which register values are the correct ones to save. If you do manage to solve this issue, please do send us an example. Myself and many other users will be very thankful.

Best wishes,
Paul

[Bongasman]

Hi Bongas (@Bongasman ), Todd and colleagues,

Unfortunately I don't have an answer for you. The DMP is (almost) a complete black box and there are still many things we do not understand about it. I believe it should be possible to read, save and restore the DMP's internal 'calibration' data, and there are methods in the library to let you read and write the DMP registers, but we we have no information or guidance on which register values are the correct ones to save. If you do manage to solve this issue, please do send us an example. Myself and many other users will be very thankful.

Best wishes, Paul

Thank you @PaulZC, If we find something helpful, we will let you know. Nevertheless you did a great job on your library thus far. I just wish InvenSense could do a library or example to address this issue.