Jetson Nano Tachometer Measurement Update Rate

Robotics & Edge Computing Jetson & Embedded Systems Jetson Nano
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1

Hello all,

I am working on an autonomous robot with Jetson Nano and I need to read the RPM signal coming from a brushless motor phase sensor. At the moment I am using the J15 pin for reading the RPM signal and I am reading the /sys/devices/pwm-fan/rpm_measured file for the measurement. However, I am getting measurements in 1 Hz which is slow for my application.

I wonder if someone knows what is the update rate of the rpm_measurement in /sys files. Does the limitation come from the sensor refresh rate or update rate of /sys files?

Thanks in advance!

3

hello ozan_f1_3,

it’s driver to wait for “tach_period” msec after enable “tach_enabled” to get right RPM value.
you should dig into kernel driver,
for example,
$L4T_Sources/r32.5.1/Linux_for_Tegra/source/public/kernel/nvidia/drivers/thermal/pwm_fan.c

please also refer to kernel documentation for the Linux PWM interface.
for example,
$L4T_Sources/r32.5.1/Linux_for_Tegra/source/public/kernel/kernel-4.9/Documentation/pwm.txt

4

Thanks a lot, I will give this a chance. I guess I can compile a new kernel module and change its update rate. I will post my results.