EBC Exercise 13 Pulse Width Modulation - Revision history

Yoder at 16:34, 31 May 2013

2013-05-31T16:34:46Z

Yoder: /* Resources */ Removed

2013-05-31T16:34:17Z

‎Resources: Removed

Yoder: /* PWM on the xM */ Removed

2013-05-31T16:33:01Z

‎PWM on the xM: Removed

Yoder: /* PWM on the Bone */

2013-05-31T16:27:15Z

‎PWM on the Bone

Yoder: Updating for 3.8

2013-05-31T16:01:36Z

Updating for 3.8

Yoder: /* The Slick Way */ Removed

2013-05-31T14:45:52Z

‎The Slick Way: Removed

Yoder: Switched to 3.8 kernel

2013-05-31T14:32:41Z

Switched to 3.8 kernel

Lobdeljt: /* Either Way */

2012-09-13T06:04:58Z

‎Either Way

Yoder: /* The Slick Way */ Added check to see if symlink is correct

2012-09-10T20:58:55Z

‎The Slick Way: Added check to see if symlink is correct

Jungeml: /* Assignment */

2012-09-09T19:35:21Z

‎Assignment

@@ Line 6: / Line 6: @@
 In a previous exercise ([[EBC Exercise 11 gpio Polling and Interrupts]]) you saw how to use the gpio to produce a square wave out using a C program and sysfs. I was able to get a 1.5kHz square wave out; however we can do much better using some built in hardware on the Beagle.
-In this exercise you will learn how to use the Beagle's pulse width modulation (pwm) hardware using the sysfs interface and also learn about pin multiplexing (pin mux) on the way.
+In this exercise you will learn how to use the Beagle's pulse width modulation (pwm) hardware using the sysfs interface.
 == PWM on the Bone ==

← Older revision		Revision as of 16:34, 31 May 2013
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	Stick a scope on the pin and see if the frequency and duty cycle are right. What's the highest frequency you can get? What's the lowest?		Stick a scope on the pin and see if the frequency and duty cycle are right. What's the highest frequency you can get? What's the lowest?
−
−	~~== Resources ==~~
−
−	~~# [[BeagleBoardPWM]] from ECE597~~
−	~~# [[BeagleBoard/GSoC/2010_Projects/Pulse_Width_Modulation]] Google SoC project~~
−	~~# [[BeagleBoardPinMux]], how to set the pin mux.~~
−	~~# [http://www.gigamegablog.com/ Buttons and PWM]~~
−	~~# [http://veter-project.blogspot.com/2011/09/real-time-enough-about-pwms-and-shaky.html Shaky PWMs]~~
−	~~# [https://groups.google.com/forum/#!searchin/beagleboard/bone$20pwm/beagleboard/alKf67dwMHI/t_tIQpJyM8wJ PWM on the bone]~~

	{{YoderFoot}}		{{YoderFoot}}

← Older revision		Revision as of 16:33, 31 May 2013
Line 45:		Line 45:

	Stick a scope on the pin and see if the frequency and duty cycle are right. What's the highest frequency you can get? What's the lowest?		Stick a scope on the pin and see if the frequency and duty cycle are right. What's the highest frequency you can get? What's the lowest?
−
−	~~== PWM on the xM ==~~
−	~~'''This section needs updating to use /sys/kernel/debug/omap_mux to get the pin MUXes.'''~~
−
−	The DM3730 has 11 general purpose timers, 4 of which (gpt8-gpt11) can be brought out of the chip and used for pulse width modulation ([http://www.ti.com/product/dm3730#technicaldocuments DM3730 TRM page 2689]). The problem is the DM3730 has more internal lines than hardware I/O pins. The solution is that I/O pins run though a MUX that selects which internal lines appear on I/O pins. A given pin can have one from as many as eight lines assigned to it.
−
−	These MUXes are set at boot time, and must be set when the kernel boots, or in u-boot. I couldn't set them during kernel boot with the 2.6.32 kernel, so I used u-boot. [[BeagleBoardPinMux]] is a good place to learn about the pin MUXing. The u-boot details are [[BeagleBoardPinMux#Setting_Mux_Through_u-boot \| here]].
−
−	[[BeagleBoardPWM]] is a nice overview of how to do PWM on the Beagle. The version of the kernel and u-boot that I've given you should already be configured to access the PWM pins. If it isn't you'll have to recompile the Kernel and u-boot.
−
−	The standard way to interface with the outside world in Linux is through Kernel Drivers. Currently there are no standard PWM driver for the Beagle, though a couple have been proposed ([https://groups.google.com/d/topic/beagleboard/RI3qTxn68bY/discussion], [http://git.billgatliff.com/pwm.git/?p=pwm.git;a=commit;h=a49cbfff0fa09bff40d328f8985a0a7a7b951d6f] and [http://git.pengutronix.de/?p=imx/linux-2.6.git;a=commit;h=137654cde98a2ffe548f47f02e7fde512bc2091c]). [[BeagleBoardPWM]] takes a more traditional MCU approach by accessing the memory mapped PWD registers directly using '''mmap''' in a C program. Although this approach works, it is really transitional until a standard can be established.
−
−	~~You could even do PWM from a shell command by using [http://esdw.wordpress.com/2010/03/25/a-useful-tool-devmem2/ devmem2] to write to the memory mapped registers from a command line.~~
−
−	~~[http://www.jumpnowtek.com/index.php?option=com_content&view=article&id=56&Itemid=63 Here's] another PWM lead.~~
−
−	~~=== Assignment ===~~
−
−	~~If your git repository is set up just:~~
−	~~beagle$ '''cd exercises'''~~
−	~~beagle$ '''git pull'''~~
−	~~beagle$ '''cd pwm'''~~
−	~~(Follow the instructions [[EBC_Exercise_01a_Getting_Exercise_Support_Materials \| here]] if you aren't set up for git.)~~
−
−	~~# Look at the files to see what they are doing.~~
−	~~# Run '''make''', then '''pwm-demo'''.~~
−	~~# Hook up a oscilloscope. (See Table 22 of the [http://beagleboard.org/static/BBxMSRM_latest.pdf Beagle System Reference manual] to see where to probe.) Are the pwm outputs doing what you expected?~~
−	~~# What's the highest frequency you can generate? What's the lowest?~~
−	~~# Create a new C program, based on pwm-demo, that takes 3 parameters, the <pwm to use>, <frequency> and <duty cycle>.~~
−	~~# Create a shell file that will call your new program and set up the three pwm's that appear on the expansion header and program them to do something interesting.~~
−	~~# Write a shell file that will do the pin MUXing using '''devmem2'''.~~
−	~~# Rewrite '''pwm-demo''' as a shell file that uses '''devmem2'''.~~

	== Resources ==		== Resources ==

@@ Line 10: / Line 10: @@
 == PWM on the Bone ==
-(Note:
+(Note: The pwm interface seems to changing. Some of this may not apply in the future.)
 The Bone has a PWM interface at <code>/sys/class/pwm/</code>. You can see what's there by:
@@ Line 22: / Line 23: @@
   beagle$ '''ls -F'''
   export  pwmchip0@  pwmchip2@  pwmchip3@  pwmchip5@  pwmchip7@  unexport
 Now you can export a pwm much list you export a gpio port
   beagle$ '''echo 1 > export'''
@@ Line 31: / Line 34: @@
   beagle$ '''echo  250000 > duty_ns'''
   beagle$ '''echo 1 > run'''
-If you have an oscilloscope try probing pin P9_21.
+If you have an oscilloscope try probing pin P9_21. I'm getting a nice clean 1kHz signal, with no variation.  Let's try a higher frequency, like 10 MHz.
-=== The Sure Way ===
+The [http://processors.wiki.ti.com/index.php/AM335x_PWM_Driver's_Guide AM335x PWM Driver's Guide] details what eCAP and eHRPWM are and gives some examples.
- beagle$ '''cd ~/exercises/pinMux'''
+Connect the LED from and watch it flash.  Try changing the frequency and duty cycle.  You may have to set the duty cycle to 0 to change the frequency.  Can you guess why?
- beagle$ '''./pinMux.sh'''
-−
-This just lists all the files in the mux directory and their contents.
-−
-=== Either Way ===
-−
-This just lists every find in the mux directory.
-−
-You can control the pin MUXing this way:
-−
- beagle$ '''cd /sys/kernel/debug/omap_mux'''
- beagle$ '''ls'''
- ain0               gpmc_ad2        lcd_data3      mii1_txd2
- ain1               gpmc_ad3        lcd_data4      mii1_txd3
- ain2               gpmc_ad4        lcd_data5      mii1_txen
- ain3               gpmc_ad5        lcd_data6      mmc0_clk
- ain4               gpmc_ad6        lcd_data7      mmc0_cmd
- ain5               gpmc_ad7        lcd_data8      mmc0_dat0
- ain6               gpmc_ad8        lcd_data9      mmc0_dat1
- ain7               gpmc_ad9        lcd_hsync      mmc0_dat2
- ...
-−
-There are some 126 pins that you can control what they output.  How do you know which one to change?  Let's use ehrpwm.1:0.  This will show up at ehrpwm1A (the 0 maps to A).  Try:
-−
- beagle$ grep ehrpwm *
- gpmc_a0:signals: gpmc_a0 | gmii2_txen | rgmii2_tctl | rmii2_txen | gpmc_a16 | pr1_mii_mt1_clk | ehrpwm1_tripzone_input | gpio1_16
- gpmc_a1:signals: gpmc_a1 | gmii2_rxdv | rgmii2_rctl | mmc2_dat0 | gpmc_a17 | pr1_mii1_txd3 | ehrpwm0_synco | gpio1_17
- '''gpmc_a2''':signals: gpmc_a2 | gmii2_txd3 | rgmii2_td3 | mmc2_dat1 | gpmc_a18 | pr1_mii1_txd2 | '''ehrpwm1A''' | gpio1_18
- gpmc_a3:signals: gpmc_a3 | gmii2_txd2 | rgmii2_td2 | mmc2_dat2 | gpmc_a19 | pr1_mii1_txd1 | ehrpwm1B | gpio1_19
- ...
-This shows that '''ehrpwm1A''' shows up in the file '''gpmc_a2'''. Look in the file
- beagle$ '''cat gpmc_a2'''
- name: gpmc_a2.gpio1_18 (0x44e10848/0x848 = 0x0007), b NA, t NA
- mode: OMAP_PIN_OUTPUT | '''OMAP_MUX_MODE7'''
- signals: gpmc_a2 | gmii2_txd3 | rgmii2_td3 | mmc2_dat1 | gpmc_a18 | pr1_mii1_txd2 | ehrpwm1A | gpio1_18
-−
-This says the MUX is presently set on pin '''7'''.  Counting starts on the left with 0.  We want pin '''6'''. So:
-−
- beagle$ '''echo 6 > gpmc_a2'''
- beagle$ '''cat gpmc_a2'''
- name: gpmc_a2.ehrpwm1A (0x44e10848/0x848 = 0x0006), b NA, t NA
- mode: OMAP_PIN_OUTPUT | '''OMAP_MUX_MODE6'''
- signals: gpmc_a2 | gmii2_txd3 | rgmii2_td3 | mmc2_dat1 | gpmc_a18 | pr1_mii1_txd2 | '''ehrpwm1A''' | gpio1_18
-−
-Now it's mode 6, which is the PWM output.  Refresh you pin MUX web page to see.
-−
-[[File:PinMux2.png]]
-−
-Notice header P9, pin 14 has changed!  Now let's turn on the PWM.
-−
- beagle$ '''cd /sys/class/pwm/ehrpwm.1\:0'''
- beagle$ '''echo 1 > run'''
- beagle$ '''echo 10 > period_freq'''
- beagle$ '''echo 25 > duty_percent'''
-−
-Note: If these command cause the SSH connection to close, you may have to get a newer version of Angstrom. Follow the instructions at [[EBC_Exercise_03_Installing_a_Beagle_OS]] and try it again.
-−
-Connect the LED from [[EBC_Exercise_10_Flashing_an_LED#Adding_your_own_LED_-_bone]] and watch it flash.  Try changing the frequency and duty cycle.  You may have to set the duty cycle to 0 to change the frequency.  Can you guess why?
 Stick a scope on the pin and see if the frequency and duty cycle are right.  What's the highest frequency you can get? What's the lowest?
 == PWM on the xM ==

@@ Line 10: / Line 10: @@
 == PWM on the Bone ==
 The Bone has a PWM interface at <code>/sys/class/pwm/</code>. You can see what's there by:
   beagle$ '''cd /sys/class/pwm'''
   beagle$ '''ls -F'''
-  ecap.0@  ecap.2@      ehrpwm.0:1@  ehrpwm.1:1@  ehrpwm.2:1@
+  export  unexport
-  ecap.1@  ehrpwm.0:0@  ehrpwm.1:0@  ehrpwm.2:0@
+Hmmm, there isn't much there.  We have to run a command to make something appear.  Try
 The [http://processors.wiki.ti.com/index.php/AM335x_PWM_Driver's_Guide AM335x PWM Driver's Guide] details what eCAP and eHRPWM are and gives some examples.  Before you can use the PWM's, you need to make sure the pin MUXes are set correctly. There are two ways to do this, the slick way (which may not work) and the sure way.

← Older revision		Revision as of 14:45, 31 May 2013
Line 18:		Line 18:

	The [http://processors.wiki.ti.com/index.php/AM335x_PWM_Driver's_Guide AM335x PWM Driver's Guide] details what eCAP and eHRPWM are and gives some examples. Before you can use the PWM's, you need to make sure the pin MUXes are set correctly. There are two ways to do this, the slick way (which may not work) and the sure way.		The [http://processors.wiki.ti.com/index.php/AM335x_PWM_Driver's_Guide AM335x PWM Driver's Guide] details what eCAP and eHRPWM are and gives some examples. Before you can use the PWM's, you need to make sure the pin MUXes are set correctly. There are two ways to do this, the slick way (which may not work) and the sure way.
−
−	~~=== The Slick Way ===~~
−
−	~~On your Bone~~
−
−	~~beagle$ '''cd exercises'''~~
−	~~beagle$ '''git pull'''~~
−	~~beagle$ '''cd pinMux'''~~
−	~~beagle$ '''ln -s $PWD/pinMux.html /var/lib/cloud9/bone101'''~~
−	~~beagle$ '''ls -ls /var/lib/cloud9/bone101/pinMux.html'''~~
−	~~0 lrwxrwxrwx 1 root root 39 Sep 6 14:19 /var/lib/cloud9/bone101/pinMux.html -> /home/root/exercises/pinMux/pinMux.html~~
−	~~beagle$ '''cd /var/lib/cloud9'''~~
−	~~beagle$ '''git pull'''~~
−	~~beagle$ '''shutdown -r now'''~~
−
−	~~Yup, after updating /var/lib/cloud9 you have to reboot.~~
−
−	Now, check the settings by browsing to [http://beagle/pinMux.html http://''bone''/pinMux.html] (where ''bone'' is the IP address of your Bone.) to see how the pins are set. You'll see something like:
−
−	~~[[File:PimMux1.png]]~~

	=== The Sure Way ===		=== The Sure Way ===

@@ Line 2: / Line 2: @@
 [[Category:ECE497]]
 {{YoderHead}}
 In a previous exercise ([[EBC Exercise 11 gpio Polling and Interrupts]]) you saw how to use the gpio to produce a square wave out using a C program and sysfs. I was able to get a 1.5kHz square wave out; however we can do much better using some built in hardware on the Beagle.

@@ Line 26: / Line 26: @@
   beagle$ '''cd pinMux'''
   beagle$ '''ln -s $PWD/pinMux.html /var/lib/cloud9/bone101'''
   beagle$ '''cd /var/lib/cloud9'''
   beagle$ '''git pull'''

@@ Line 137: / Line 137: @@
 # Look at the files to see what they are doing.
-# Run '''make''', then '''pwd-demo'''.
+# Run '''make''', then '''pwm-demo'''.
-# Hook up a oscilloscope.  (See Table 22 of the [http://beagleboard.org/static/BBxMSRM_latest.pdf Beagle System Reference manual] to see where to probe.) Are the pwd outputs doing what you expected?
+# Hook up a oscilloscope.  (See Table 22 of the [http://beagleboard.org/static/BBxMSRM_latest.pdf Beagle System Reference manual] to see where to probe.) Are the pwm outputs doing what you expected?
 # What's the highest frequency you can generate?  What's the lowest?
 # Create a new C program, based on pwm-demo, that takes 3 parameters, the <pwm to use>, <frequency> and <duty cycle>.