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From:   Jean-Baptiste Maneyrol <JManeyrol@invensense.com>
To:     Andreea Lutac <andreea.lutac@fixposition.ch>
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Subject: Re: ICM20602 buffer issues with the inv_mpu6050 driver
Thread-Topic: ICM20602 buffer issues with the inv_mpu6050 driver
Thread-Index: AQHVD8GjTipz5tzQVUSj/IxhuD+TzaZ3NPiE
Date:   Wed, 22 May 2019 14:33:44 +0000
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Hello,=0A=
=0A=
I had a look inside the driver to verify the buffer implementation. It look=
s correct to me. I don't see where the problem can come from. I am sorry I =
don't have a setup currently to test in live.=0A=
=0A=
For sure you can have a different result by reading the buffer through the =
char device file compared to reading the raw sysfs entry. The buffer is tak=
ing the data from the FIFO and the raw sysfs from the sensor data registers=
.=0A=
=0A=
You can perhaps test value 1 by 1 in the buffer, and verify the correctness=
 of every attributes. If you can also send a complete buffer log that would=
 be helpful.=0A=
Every data is 2 bytes long and in the following order: accel_x, accel_y, ac=
cel_z, temp, gyro_x, gyro_y, gyro_z=0A=
=0A=
Best regards,=0A=
JB Maneyrol=0A=
=0A=
From: Andreea Lutac <andreea.lutac@fixposition.ch>=0A=
Sent: Tuesday, May 21, 2019 12:40=0A=
Cc: Jean-Baptiste Maneyrol; stevemo@skydio.com; jic23@kernel.org; knaack.h@=
gmx.de; lars@metafoo.de; pmeerw@pmeerw.net; linux-iio@vger.kernel.org; linu=
x-kernel@vger.kernel.org=0A=
Subject: ICM20602 buffer issues with the inv_mpu6050 driver=0A=
=A0=0A=
Hello,=0A=
=0A=
I've been trying to get some data samples from the ICM20602 IMU using the m=
pu6050 driver which recently added support for it, but I'm encountering an =
issue with the ordering of the data in the FIFO.=0A=
According to the specs of the device, if the accel and gyro XYZ channels ar=
e enabled, then the hardware FIFO is filled with 14 bytes corresponding to =
the following channels: accel_x, accel_y, accel_z, temp, anglvel_x, anglvel=
_y, anglvel_z. However, when reading out the buffer, the value I get for an=
glvel_x seems to actually be the temperature. This=A0 occurs both when read=
ing with iio_channel_read (via libiio) and also if I read directly from /de=
v/iio:device with only in_anglvel_x_en set. But in_anglvel_x_raw reports co=
rrect values, which made me suspect that maybe somewhere in the driver this=
 interleaved temp channel is not accounted for in the buffer structure.=0A=
=0A=
I had a look at the driver code and inv_mpu6050_read_fifo() in particular, =
but I can't identify anything amiss. I've applied the recent patch that add=
ed the extra 2 temperature bytes ( ), but the problem persists. So far I've=
 tried changing the size of the data buffer, defined in inv_mpu_iio.h:=0A=
=0A=
/* 6 + 6 round up and plus 8 */=0A=
#define INV_MPU6050_OUTPUT_DATA_SIZE=A0=A0=A0=A0 24=0A=
=0A=
from 24 to 32, according to the intuition that 24 corresponds to readings w=
ithout temperature (i.e. 6 bytes for accel, rounded up to 8 + 6 bytes for g=
yro, rounded up to 8 + 8 bytes for the timestamp =3D 24) and thus another 8=
 bytes would be needed, but that doesn't seem to have solved it.=0A=
=0A=
I'm quite new to driver development though, so I think there might be somet=
hing I'm not getting. I would be really grateful if anyone could shed some =
light over what's happening here or give some advice as to what I could be =
doing wrong.=0A=
=0A=
Best regards,=0A=
Andreea Lutac=0A=
=0A=