How to enable ePWM by setting register on AM335x (Beaglebone) ?

Kim Seonghyun

Hi,

I am working on Beaglebone (AM335x)and tried to control PWM.

I have a plan to control PWM by using "register" only with datasheet (http://www.ti.com/lit/ug/spruh73i/spruh73i.pdf) and would like not to use "pwm_test device driver" because of real time issue.

I found it controlling "frequency" and "duty cycle" by using register only is quite easy. (https://github.com/zedoul/rtdm-pwm/blob/master/rtdm/mf2044-pwm-drv.c)

but controlling "init/deinit PWM" is quite confusing and still could not make it. I read kernel source - pwm-tipwmss.c, pwm-tiehrpwm.c, and pwm_test.c, but still could not get it too. Also I asked "Beaglebone google group" but they don't make it too. So I guess this thread is my last chance.

So my questions are :

* Is it possible to enable/disable PWM by controlling "registers" only? If not, which prerequisites should be placed in order to make it?

* Could you let me know the sample code for enabling PWM which is equivalent to "echo bone_pwm_P9_14 > /sys/devices/bone_capemgr.7/slots" ?

* Could you let me know the document to read in order to activate PWM?

Thanks in advance.

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

Hi Kim,

Perhaps Starterware is what you are looking for. Here is a link to PWM programming in Starterware: http://processors.wiki.ti.com/index.php/StarterWare_EHRPWM

0 Kim Seonghyun over 10 years ago in reply to Biser Gatchev-XID

Prodigy 50 points

Thanks, Biser Gatchev-XID. I will check it.

Could you let me know where is the manual or how can I use those functions? I use "grep" to see whether some functions are exist or not in driver/pwm folder which imports pwm-tiehrpwm.c and etc and I couldn't find them.

I mean I need to know which header I should include at least.

0 Biser Gatchev-XID over 10 years ago in reply to Kim Seonghyun

TI__Guru**** 393215 points

The Starterware manual can be found here: http://processors.wiki.ti.com/index.php/StarterWare_02.00.01.01_User_Guide

This is the Starterware download page, with links to documentation: http://software-dl.ti.com/dsps/dsps_public_sw/am_bu/starterware/latest/index_FDS.html

0 Kim Seonghyun over 10 years ago in reply to Biser Gatchev-XID

Prodigy 50 points

Thank you for your response.

It could be solution, however, it seems like that I still don't get my initial answer - how to enable pwm by using register. I really would like to control PWM by using "only" registers"

Is it not possible? If possible, I will be very happy if you let me know the example or the document (with chapter which is related)

0 Biser Gatchev-XID over 10 years ago in reply to Kim Seonghyun

TI__Guru**** 393215 points

Have you seen section 15.2.3 in the AM335X TRM rev.I? There are examples there with corresponding initialization sequences. Other than that I don't think any public code exists, other than Starterware.

0 Kim Seonghyun over 10 years ago in reply to Biser Gatchev-XID

Prodigy 50 points

Of course I checked that section, especially Table 15-43. EPWM1 Initialization for Figure 15-58 / Table 15-44. EPWM1 Initialization for Figure 15-58 / Table 15-45. EPWM1 Initialization for Figure 15-58. However, some register value couldn't changed before I launch "pwm_test".

For example, "TBPRD" register, which need to be changed to 0x578 for EPWM2. It can not be changed until launching pwm_test.

I am certain there are some prerequisite action before that but I couldn't find any in datasheet. One of prerequisite is EPWMSS1_CLK_CTRL which need to become "0x2" is one of them. But I do not know about the others.

StarterWare would be a detour, but I really would like to fix in straight way.

I really want to see how I can change TBPRD register without launching pwm_test.

0 Biser Gatchev-XID over 10 years ago in reply to Kim Seonghyun

TI__Guru**** 393215 points

From the AM335X TRM, section 15.2.4.6:

Shadowing of this register is enabled and disabled by the TBCTL[PRDLD] bit. By default this register is shadowed.

(a) If TBCTL[PRDLD] = 0, then the shadow is enabled and any write or read will automatically go to the shadow register. In this case, the active register will be loaded from the shadow register when the time-base counter equals zero.

(b) If TBCTL[PRDLD] = 1, then the shadow is disabled and any write or read will go directly to the active register, that is the register actively controlling the hardware.

0 Kim Seonghyun over 10 years ago in reply to Biser Gatchev-XID

Prodigy 50 points

It seems like it doesn't work too.

whenever I tried to fix TBCTL[PRDLD] = 0 or 1, I couldn't fix TBPRD.

The process is I set TBCTL[PRDLD] = 1 to set value directly to TBPRD, then I set TBPRD and just check what happened.

What I expected is TBPRD is changed but what I actually saw is "not changed"

my code is like this

orReg(EPWM1_TBCTL,0x1 << 3)

register_fix(EPWM1_TBPRD,"PRD",0x258)

(https://github.com/zedoul/rtdm-pwm/blob/master/testcodes/initPWM.py)

0 richa mehndiratta over 10 years ago in reply to Kim Seonghyun

Prodigy 10 points

could you solve the issue?....m too stuck at accessing pwm through registers

0 Don Lawrence over 9 years ago in reply to richa mehndiratta

Expert 1315 points

me too. the starterware wiki

StarterWare EHRPWM

Revision as of 15:20, 1 March 2012 by Sujithkv

at http://processors.wiki.ti.com/index.php?oldid=99133

references functions that are nowhere in the starterware device tree or drivers.

i have been pouring over the TRM spruh73j for days to no avail.

i have been writing drivers for decades, so i think a simple rc-servo driver example

is not too much to ask for. pleeeeeeeze

thank you...........don

0 Matthijs van Duin over 9 years ago in reply to Don Lawrence

Mastermind 8020 points

In case you still care (or anyone else who might find this thread): be sure to set the appropriate tbclken bit in the pwmss_ctrl register of the control module.

0 Don Lawrence over 9 years ago in reply to Matthijs van Duin

Expert 1315 points

Hi Matt. I am not sure what you are driving at.

However, I pretty much hacked the PWM and posted it here.

Search Beaglebone bare metal PWM driver.

btw, have you tried i2c? I need help with this & gcc.

later............dd

0 Matthijs van Duin over 9 years ago in reply to Don Lawrence

Mastermind 8020 points

Don Lawrence said:
Hi Matt. I am not sure what you are driving at.

The timebase clock enable bits in the control module are a likely candidate for the "prequisite action" the original poster was looking for, they are easy to overlook.

Don Lawrence said:
btw, have you tried i2c?

I do in fact have experience with that (buggy piece of ***) peripheral, but please open a new thread with your question about it.

Processors

Processors forum

How to enable ePWM by setting register on AM335x (Beaglebone) ?

StarterWare EHRPWM