Document how to test eQEP with Rotary Encoder

Related to feature request in #122

Author: pdp7

doc/rotary-encoder-eqep-test.md

@@ -0,0 +1,56 @@
+I'm using P8.11 and P8.12 for testing a rotary encoder.
+
+Using cape-universal:
+```
+debian@beaglebone:~$ cat /sys/devices/platform/bone_capemgr/slots
+ 0: PF----  -1 
+ 1: PF----  -1 
+ 2: PF----  -1 
+ 3: PF----  -1 
+ 4: P-O-L-   0 Override Board Name,00A0,Override Manuf,univ-all
+ 5: P-O-L-   1 Override Board Name,00A0,Override Manuf,BB-ADC
+```
+
+/boot/uEnv.txt:
+```
+uname_r=4.4.47-ti-r87
+dtb=am335x-boneblack-overlay.dtb
+cmdline=coherent_pool=1M quiet cape_universal=enable
+```
+
+Configure the pin mode for eQEP:
+```
+debian@beaglebone:~$ config-pin p8.11 qep && config-pin p8.12 qep
+
+debian@beaglebone:~$ config-pin -q p8.11 && config-pin -q p8.12 
+P8_11 Mode: qep
+P8_12 Mode: qep
+```
+
+System info:
+```
+debian@beaglebone:~$ uname -a
+Linux beaglebone 4.4.47-ti-r87 #1 SMP Mon Feb 6 22:21:49 UTC 2017 armv7l GNU/Linux
+debian@beaglebone:~$ cat /etc/debian_version 
+8.7
+debian@beaglebone:~$ sudo cat /etc/dogtag 
+BeagleBoard.org Debian Image 2015-12-07
+```
+
+Check the position:
+```
+debian@beaglebone:~$ find /sys/devices |grep eqep |grep position$
+/sys/devices/platform/ocp/48302000.epwmss/48302180.eqep/position
+/sys/devices/platform/ocp/48304000.epwmss/48304180.eqep/position
+/sys/devices/platform/ocp/48300000.epwmss/48300180.eqep/position
+debian@beaglebone:~$ cat `find /sys/devices |grep eqep |grep position$`
+0
+-3251
+0
+debian@beaglebone:~$ watch -n 1 cat /sys/devices/platform/ocp/48304000.epwmss/48304180.eqep/position
+```
+
+For P8.11 and P8.12:
+```
+/sys/devices/platform/ocp/48304000.epwmss/48304180.eqep/position
+```