Problems with UART

[thebrianbug]

I am unable to set up UART with my board. My code runs with no errors, but no signal shows on the oscilloscope - it's 100% a voltage low. The "Serial is open!" message does show in the console. This time, invoking the script with sudo does not help. I've also tried to open a terminal with minicom to view the output for the tty. Here's my test code:

import Adafruit_BBIO.UART as UART
import serial
 
UART.setup("UART1")
 
ser = serial.Serial(port = "/dev/ttyO1", baudrate=9600)
ser.close()
ser.open()
if ser.isOpen():
	print "Serial is open!"
ser.write("Hello World!")
ser.close()

I've also tried the following experiment.

#first terminal window:
minicom -b 9600 -D /dev/ttyO1
 
#second terminal window:
minicom -b 9600 -D /dev/ttyO2

#now type in one terminal and press enter. Expect to view characters in second window.

No matter what I do, no data is sent over UART. Any suggestions or ideas? Here's the state of my board.

debian@beaglebone:/var/lib/cloud9/senior_design$ apt-get -v
apt 1.4.8 (armhf)
Supported modules:
*Ver: Standard .deb
*Pkg:  Debian dpkg interface (Priority 30)
 Pkg:  Debian APT solver interface (Priority -1000)
 Pkg:  Debian APT planner interface (Priority -1000)
 S.L: 'deb' Debian binary tree
 S.L: 'deb-src' Debian source tree
 Idx: Debian Source Index
 Idx: Debian Package Index
 Idx: Debian Translation Index
 Idx: Debian dpkg status file
 Idx: Debian deb file
 Idx: Debian dsc file
 Idx: Debian control file
 Idx: EDSP scenario file
 Idx: EIPP scenario file
debian@beaglebone:/var/lib/cloud9/senior_design$ cat /etc/dogtag
cat /sys/devices/platform/bone_capemgr/slots
cat /boot/uEnv.txt
config-pin -q p9.14
uname -aBeagleBoard.org Debian Image 2017-10-17
debian@beaglebone:/var/lib/cloud9/senior_design$ cat /etc/debian_version
9.2
debian@beaglebone:/var/lib/cloud9/senior_design$ cat /proc/cmdline
console=ttyO0,115200n8 bone_capemgr.uboot_capemgr_enabled=1 root=/dev/mmcblk1p1 ro rootfstype=ext4 rootwait coherent_pool=1M net.ifnames=0 quiet
debian@beaglebone:/var/lib/cloud9/senior_design$ cat /sys/devices/platform/bone_capemgr/slots
cat: /sys/devices/platform/bone_capemgr/slots: No such file or directory
debian@beaglebone:/var/lib/cloud9/senior_design$ cat /boot/uEnv.txt
#Docs: http://elinux.org/Beagleboard:U-boot_partitioning_layout_2.0

uname_r=4.14.0-rc7-ti-r6
#uuid=
#dtb=


###U-Boot Overlays###
###Documentation: http://elinux.org/Beagleboard:BeagleBoneBlack_Debian#U-Boot_Overlays
###Master Enable
enable_uboot_overlays=1
###
###Overide capes with eeprom
#uboot_overlay_addr0=/lib/firmware/<file0>.dtbo
#uboot_overlay_addr1=/lib/firmware/<file1>.dtbo
#uboot_overlay_addr2=/lib/firmware/<file2>.dtbo
#uboot_overlay_addr3=/lib/firmware/<file3>.dtbo
###
###Additional custom capes
#uboot_overlay_addr4=/lib/firmware/<file4>.dtbo
#uboot_overlay_addr5=/lib/firmware/<file5>.dtbo
#uboot_overlay_addr6=/lib/firmware/<file6>.dtbo
#uboot_overlay_addr7=/lib/firmware/<file7>.dtbo
###
###Custom Cape
#dtb_overlay=/lib/firmware/<file8>.dtbo
###
###Disable auto loading of virtual capes (emmc/video/wireless/adc)
#disable_uboot_overlay_emmc=1
#disable_uboot_overlay_video=1
#disable_uboot_overlay_audio=1
#disable_uboot_overlay_wireless=1
#disable_uboot_overlay_adc=1
###
###PRUSS OPTIONS
###pru_rproc (4.4.x-ti kernel)
uboot_overlay_pru=/lib/firmware/AM335X-PRU-RPROC-4-4-TI-00A0.dtbo
###pru_uio (4.4.x-ti & mainline/bone kernel)
#uboot_overlay_pru=/lib/firmware/AM335X-PRU-UIO-00A0.dtbo
###
###Cape Universal Enable
enable_uboot_cape_universal=1
###
###Debug: disable uboot autoload of Cape
#disable_uboot_overlay_addr0=1
#disable_uboot_overlay_addr1=1
#disable_uboot_overlay_addr2=1
#disable_uboot_overlay_addr3=1
###
###U-Boot fdt tweaks...
#uboot_fdt_buffer=0x60000
###U-Boot Overlays###

cmdline=coherent_pool=1M net.ifnames=0 quiet

#In the event of edid real failures, uncomment this next line:
#cmdline=coherent_pool=1M net.ifnames=0 quiet video=HDMI-A-1:1024x768@60e

##Example v3.8.x
#cape_disable=capemgr.disable_partno=
#cape_enable=capemgr.enable_partno=

##Example v4.1.x
#cape_disable=bone_capemgr.disable_partno=
#cape_enable=bone_capemgr.enable_partno=

##enable Generic eMMC Flasher:
##make sure, these tools are installed: dosfstools rsync
#cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh

debian@beaglebone:/var/lib/cloud9/senior_design$ config-pin -q p9.14
P9_14 Mode: pwm
debian@beaglebone:/var/lib/cloud9/senior_design$ uname -a
Linux beaglebone 4.14.0-rc7-ti-r6 #1 SMP Mon Oct 30 17:10:41 UTC 2017 armv7l GNU/Linux

[thebrianbug]

For reference, I've connected my BBB according the this tutorial which I got the code from: https://learn.adafruit.com/setting-up-io-python-library-on-beaglebone-black/uart

[RobertCNelson]

for the usarts you need to set the pinmux:

config-pin P9.26 uart
config-pin P9.24 uart

But now that i know how the pwm mux setup in adafruit-io, it wouldn't be to hard to change that in the library too.

[pdp7]

@RobertCNelson thanks for the suggestion

@bmcilw1 Please use config-pin as Robert mentioned above to configure P9.24 and P9.26 for UART1

Verify the pin mode is set with:

cat /sys/devices/platform/ocp/ocp:P9_24_pinmux/state
cat /sys/devices/platform/ocp/ocp:P9_26_pinmux/state

[thebrianbug]

Interesting, I now see some different behavior. Here's the verification for my uart setup

debian@beaglebone:/var/lib/cloud9/senior_design$ config-pin P9.26 uart
debian@beaglebone:/var/lib/cloud9/senior_design$ config-pin P9.24 uart
debian@beaglebone:/var/lib/cloud9/senior_design$ cat /sys/devices/platform/ocp/ocp:P9_24_pinmux/state
uart
debian@beaglebone:/var/lib/cloud9/senior_design$ cat /sys/devices/platform/ocp/ocp:P9_26_pinmux/state
uart

Now, I can type in window 1, but it still doesn't show up in window 2.

To verify that I'm not crazy, here's my pin connections of my board:

[thebrianbug]

And... I figured it out.

1. I also needed to configure pin 21 and 22.
2. I was connected to the wrong pins :) oops

debian@beaglebone:/var/lib/cloud9/senior_design$ config-pin P9.26 uart          debian@beaglebone:/var/lib/cloud9/senior_design$ config-pin P9.24 uart          debian@beaglebone:/var/lib/cloud9/senior_design$ config-pin P9.21 uart
debian@beaglebone:/var/lib/cloud9/senior_design$ config-pin P9.22 uart
debian@beaglebone:/var/lib/cloud9/senior_design$ cat /sys/devices/platform/ocp/ocp:P9_24_pinmux/state
uart
debian@beaglebone:/var/lib/cloud9/senior_design$ cat /sys/devices/platform/ocp/ocp:P9_26_pinmux/state
uart
debian@beaglebone:/var/lib/cloud9/senior_design$ cat /sys/devices/platform/ocp/ocp:P9_21_pinmux/state
uart
debian@beaglebone:/var/lib/cloud9/senior_design$ cat /sys/devices/platform/ocp/ocp:P9_22_pinmux/state
uart

Yes!!

[thebrianbug]

Why do I need to configure these pins? Shouldn't these be the default settings? config-pin P9.26 uart should be uart by default to me because the pinout diagram marks it as such... @pdp7 ?

[pdp7]

I also needed to configure pin 21 and 22.

Ah ok, that makes sense as UART2 is P9.21 and P9.22.

So for the loopback test, this is needed:

config-pin P9.21 uart  # UART2_TXD
config-pin P9.22 uart  # UART2_RXD
config-pin P9.24 uart  # UART1_TXD
config-pin P9.26 uart  # UART1_RXD

[thebrianbug]

Correct. Is that expected behavior?

[pdp7]

@bmcilw1 Yes, config-pin is used on the current image to control pin mode. I intend to add the ability for Adafruit_BBIO set pin mode with config-pin. Refer to issue #158

[RobertCNelson]

Default state has been gpio_pd with input_en for a long time..

[thebrianbug]

I'm ready to close if no one has any additional stuff here. However, I think that the need to configure pins as well as an example should probably be mentioned in the README since many of the examples won't work without it.

[pdp7]

@bmcilw1 thanks, I've updated the README to document the instructions for this issue: b4767a3