PWM documentation and/logic for kernel 4.9.XX

[Co M]

Hi,

I am using C blacklib to handle some i2c and spi devices. Also I have few PWM's  P9_14 and 16 let's say.

I learned the hard way that P9_14 and P9_16 are to be    found in '48302200'. For P9_14 for example

/sys/devices/platform/ocp/48302000.epwmss/48302200.pwm/pwm/pwmchipX  

which is a link from

/sys/class/pwm/pwmchip3/

became available as pwm0 after echoing 0 to  /sys/class/pwm/pwmchip3/export

as

root@beaglebone:/sys/class/pwm/pwmchip3/pwm0# pwd
/sys/class/pwm/pwmchip3/pwm0
root@beaglebone:/sys/class/pwm/pwmchip3/pwm0# ls -l
total 0
-rw-rw-r-- 1 root pwm 4096 Feb 22 03:14 capture
-rw-rw-r-- 1 root pwm 4096 Feb 22 03:14 duty_cycle
-rw-rw-r-- 1 root pwm 4096 Feb 22 03:14 enable
-rw-rw-r-- 1 root pwm 4096 Feb 22 03:14 period
-rw-rw-r-- 1 root pwm 4096 Feb 22 03:14 polarity
drwxrwxr-x 2 root pwm    0 Feb 22 03:14 power
-rw-rw-r-- 1 root pwm 4096 Feb 22 03:14 uevent
root@beaglebone:/sys/class/pwm/pwmchip3/pwm0#

The blacklib still doing old slot way of finding out which /sys/... files are  matching  for P9_14 pwm, going
from symbolic links to some hardcoded PXY->1,2,3 mapping finally to find out the /sys/class/.../pwm/period.. and such...

My question is:

   How do I determine which X,Y from /sys/class/pwm/pwmchipX/pwmY  maps to (X,Y) of a pwm pin PX_Y 

Thank you

 

[James Fitzsimons]

Hi there,

I've just gone through this myself, and you've already figured out all you need to know. The pwmchipX mapping can change on boot so you can't rely on the /sys/class/pwm structure. Figure out which address maps the epwmss device you want to use and navigate down the /sys/device tree as you have already posted. i.e. /sys/devices/platform/ocp/48302000.epwmss/48302200.pwm/pwm/pwmchipX  

See Roberts response to my question here https://groups.google.com/forum/#!category-topic/beagleboard/software/uAHEiJTkE5E

FWIW I found the Technical Reference Manual for the AM335x which has all the addresses for the peripherals here https://blog.dest-unreach.be/wp-content/uploads/2017/07/AM335x-TRM.pdf - it doesn't seem to be on the TI site anymore, at least not that I could find.

HTH,

James Fitzsimons

[evilwulfie]

http://www.ti.com/lit/pdf/spruh73

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