Dietpi: RPi Zero W | Serial Terminal via UART did not work

[k-plan]

Creating a bug report/issue:

Required Information:

• DietPi Version | cat /DietPi/dietpi/.version
  => DietPi v6.7 with Kernel: Linux RPi-Zero-W 4.14.34+ #1110 Mon Apr 16 14:51:42 BST 2018 armv6l GNU/Linux
• SBC Device (EG: RPi 3)? => RPi Zero W v1.3
• Power supply used (EG: 5v 1A RAVpower)? 5.1V/2,5A T5875DV Stontronics
• SD card used (EG: Sandisk ultra)? => SanDisk 8GB
• Distro (EG: Jessie) | uname -a? => Debian Stretch

Additional Information (if applicable):

• Software title?

#Serial Console: Set to 1 if you require a serial console during 1st run of DietPi.
CONFIG_SERIAL_CONSOLE_ENABLE=1

• Can this issue be replicated on a fresh installation of DietPi?

• Yes!

Expected behaviour:

• Connect any 3,3V USB-to-UART converter to RPi Pi: 1-8-10 , open serial Terminal with 115200-8-none-1-none and power up your RPi

Actual behaviour:

• Device boot up, but no serial terminal output

Steps to reproduce:

• Take a RPi Zero W, RPi 3B or RPi 3B+ and check it out

Extra details:

• It take a while, to get it to work.

• It is a missing parameter in /boot/config.txt :

# Enable UART
enable_uart=1

This problem is described only for RPi 3 so far, so it take some days, to find it out. It should happen on all devices with onboard BT.

https://www.raspberrypi.org/forums/viewtopic.php?t=141195

http://www.netzmafia.de/skripten/hardware/RasPi/RasPi_Serial.html

Änderungen beim Raspberry Pi Modell 3
Das BCM2837 auf dem Raspberry Pi3 hat 2 UARTs (wie auch seine Vorgänger), jedoch zur Unterstützung Die Bluetooth-4.2-Funktionalität des voll ausgestatteten PL011-UART wurde von den Header-Pins auf den Bluetooth-Chip verschoben und der Mini-UART auf den Header-Pins 8 und 10 verfügbar gemacht. Der Mini-UART ist eine kleine Variante des ursprünglichen UART, die neben einem geringen Durchsatz auch nicht mehr so stabil ist wie zuvor. Die Baud-Rate des Mini-UART wird vom System-Takt (Videocore IV) abgeleitet. Das bedeutet, dass die Baud-Rate nicht mehr stabil bleibt, sondern je nach CPU-Auslastung stark schwankt. Deshalb schlagen die Entwickler vor, den Core-Takt fest auf 250 MHz einzustellen (siehe unten).
...
Durch das Ändern der Datei/boot/config.txtkann die Abhängigkeit vom System Clock durch Hinzufügen der folgende Zeile am Ende der Datei fest eingestellt werden:
core_freq=250
Dies behebt das Timing-Problem und scheint wenig Einfluss auf andere Dinge zu haben. Die SPI-Taktfrequenz und ARM Timer sind ebenfalls abhängig vom System Clock.
Aus irgendeinem seltsamen Grund ist ab dem Kernel 4.4.9 "DISABLE UART" die Standard-Voreinstellung - vermutlich, um Konflikte mit Bluetooth zu verhindern. Um die serielle Schnittstelle zu aktivieren, müssen Sie enable_uart=1 in der Datei /boot/config.txt setzen. Dies behebt angeblich auch die core_freq-Problematik, so dass der obige Eintrag ggf. nicht mehr notwendig ist. Wer sicher gehen will, schreibt auf jeden Fall beides in die Datei/boot/config.txt:

core_freq=250
enable_uart=1
Wenn Sie Bluetooth nicht verwenden, ist es möglich, die beiden seriellen Ports im Devicetree zu vertauschen oder Bluetooth mittels Devicetree-Overlay ganz abzuschalten. Zum Vertauchen fügen Sie am Ende der Datei /boot/config.txtdie Zeile
dtoverlay=pi3-miniuart-bt
hinzu. Nach einem Neustart funktioniert die UART-Zuordnung wieder wie in den Vorgängerversionen. Mittels pi3-disable-bt kann man Bluetooth komplett abschalten. Dann muss aber auch noch das bluetooth-Modem deaktiviert werden, was über systemctl mit dem folgenden Kommando erreicht wird:
sudo systemctl disable hciuart

Have cross check with a old RPi B+:

• Serial terminal and login work without enable_uart=1 only CONFIG_SERIAL_CONSOLE_ENABLE=1 is needed
• but it works as well with this parameter

RPi Zero W:

• only: CONFIG_SERIAL_CONSOLE_ENABLE=1 => No serial output

• CONFIG_SERIAL_CONSOLE_ENABLE=0 and enable_uart=1 => serial output until login

• CONFIG_SERIAL_CONSOLE_ENABLE=1 and enable_uart=1 => serial output and serial login possible

[Fourdee]

@k-plan

Thanks 👍

I'll take a look when I can.

[Fourdee]

@k-plan

Great writeup, research, makes this much easier to implement/test 👍

Notes:

This allegedly also fixes the core_freq problem, so that the above entry may no longer be necessary. If you want to be sure, be sure to write both in the file /boot/config.txt:

we'll try adding enable_uart=1 for all systems, then test:
NB: will require a new image, as automation of this setting applied during initial boot stage.

• RPi 3
• RPi 3B+
• RPi Zero W

Default is disabled:

root@DietPi:~# vcgencmd get_config enable_uart
enable_uart=0

[Fourdee]

New image completed, with updated boot code. Seems to be fine, however, need to verify with serial connection:

https://dietpi.com/downloads/testing/DietPi_RPi-ARMv6-Stretch.7z

---

Removing TTYAMA0 from /boot/cmdline.txt provides same processes as above, probably no longer required?

[k-plan]

@Fourdee

Testing DietPi_v6.7_RPi-ARMv6-Stretch.img on RPi Zero W (always fresh install):

• 1.)
  Settings:

#-------Serial/UART-----
enable_uart=0

and

#Serial Console: Set to 1 if you require a serial console during 1st run of DietPi.
CONFIG_SERIAL_CONSOLE_ENABLE=1

• first phase inital boot => filesystem resize => NO serial output

• second phase inital boot => intital setup => NO serial output => you have to do inital setup via ssh => auto reboot

• second boot (after finish inital setup) => serial output of boot messages and login is possible

. . . 
[  OK  ] Started DietPi-Boot.
[  OK  ] Started DietPi-PostBoot.
[  OK  ] Started rc.local backwards compatibility.
         Starting Terminate Plymouth Boot Screen...
         Starting Hold until boot process finishes up...
[  OK  ] NTPD: time sync | Completed
[  OK  ] Root access verified.

 DietPi-Services
─────────────────────────────────────────────────────
 Mode: start


Raspbian GNU/Linux 9 RPi-Zero-W ttyS0

[  OK  ] DietPi-Services | start : cron
[ SUB1 ] DietPi-Process_tool > Apply
[  OK  ] DietPi-Process_tool | Cron (894) : Nice      0
[  OK  ] DietPi-Process_tool | Cron (894) : Affinity  0
[  OK  ] DietPi-Process_tool | Cron (894) : Scheduler SCHED_OTHER 0
[  OK  ] DietPi-Process_tool | DHCP Client (631) : Nice      0
[  OK  ] DietPi-Process_tool | DHCP Client (631) : Affinity  0
[  OK  ] DietPi-Process_tool | DHCP Client (631) : Scheduler SCHED_OTHER 0
[  OK  ] DietPi-Process_tool | Dropbear (260) : Nice      0
[  OK  ] DietPi-Process_tool | Dropbear (260) : Affinity  0
[  OK  ] DietPi-Process_tool | Dropbear (260) : Scheduler SCHED_OTHER 0
[  OK  ] DietPi-Process_tool | Completed


 ───────────────────────────────────────
 DietPi     | 16:43 | Fri 11/05/18
 ───────────────────────────────────────
 v6.7       | RPi Zero W (armv6l)
 ───────────────────────────────────────
 eth0       | 192.168.88.95
 ───────────────────────────────────────
 Default Login:
 Username = root
 Password = dietpi

 Please login to continue

---

• 2.)
  Settings:

#-------Serial/UART-----
enable_uart=1

and

#Serial Console: Set to 1 if you require a serial console during 1st run of DietPi.
CONFIG_SERIAL_CONSOLE_ENABLE=1

• first phase inital boot => filesystem resize => serial output

• second phase inital boot => intital setup => serial output, BUT NO login prompt, so it is impossible to login via serial terminal => you have to do inital setup via ssh => auto reboot => now serial output again

• second boot (after finish inital setup) => serial output of boot messages and login is possible

---

If you want to have a serial console during 1st run of DietPi, we must do it the other way around.

• a.) enable serial console here: https://github.com/Fourdee/DietPi/blob/master/PREP_SYSTEM_FOR_DIETPI.sh#L1111-L1112

• b.) enable_uart=1 in config.txt per default :
  https://github.com/Fourdee/DietPi/blob/testing/config.txt#L77-L78

• c.) leave CONFIG_SERIAL_CONSOLE_ENABLE=0 as default, so serial console will be switched off during inital boot

It should be the same for the other devices: https://github.com/Fourdee/DietPi/blob/dfa9db43cea447fe741f590b4bda3ffc5088228e/dietpi/func/dietpi-set_hardware#L1423-L1496

At the moment, I only can check RPi-Zero-W. No RPi 3B, no RPi 3B+ or Odroids.

[Fourdee]

@k-plan

Ok, yep, we can enable serial console by default, then disable as needed during 1st run 👍

[k-plan]

@Fourdee

Ok, yep, we can enable serial console by default, then disable as needed during 1st run

Yep, this is what I mean. I agree with that. :+1:

[Fourdee]

Ok, just need to update the RPi image, then i'll post link again.

[Fourdee]

~forgot to change CONFIG_SERIAL_CONSOLE_ENABLE=, will do it again.~

New image ready for testing:
https://dietpi.com/downloads/testing/DietPi_RPi-ARMv6-Stretch.7z

[Fourdee]

NB, need to redo image before setting live. Did not run through dietpi-update patches, few things not removed (eg: .bashrc entries etc).

[k-plan]

@Fourdee

New image ready for testing:

Have do some test with this image.

• 1.) enabel serial terminal

#-------Serial/UART-----
#NB: enabled for 1st run only, if you want to keep this setting, please set CONFIG_SERIAL_CONSOLE_ENABLE=1 in dietpi.txt
enable_uart=1


#Serial Console: Set to 1 if you require a serial console.
#   NB: Serial console is always enabled by default for 1st run setup, then disabled afterwards, unless set below.
CONFIG_SERIAL_CONSOLE_ENABLE=1

Work as expected. You see all messages, can login via serial terminal and finish inital setup.

👍

---

• 2.) (default)

#-------Serial/UART-----
#NB: enabled for 1st run only, if you want to keep this setting, please set CONFIG_SERIAL_CONSOLE_ENABLE=1 in dietpi.txt
enable_uart=1


#Serial Console: Set to 1 if you require a serial console.
#   NB: Serial console is always enabled by default for 1st run setup, then disabled afterwards, unless set below.
CONFIG_SERIAL_CONSOLE_ENABLE=0

We see some [FAILED] and [ TIME ] messages in seral terminal, put I thnk, it's okay.
After the last message appears, no login prompt, no login possible via serial terminal.

...

 INFO ] DietPi-Drive_Manager | Checking RootFS R/W access. Please wait...
[  OK  ] DietPi-Drive_Manager | RootFS R/W access.


 DietPi-Set_Hardware
─────────────────────────────────────────────────────
 Mode: serialconsole (disable)

[ INFO ] DietPi-Set_Hardware | Disabling known serial-getty services, please wait...
[FAILED] Failed to start [email protected].
See 'systemctl status [email protected]' for details.
[FAILED] Failed to start [email protected].
See 'systemctl status [email protected]' for details.
[FAILED] Failed to start [email protected].
See 'systemctl status [email protected]' for details.
[FAILED] Failed to start [email protected].
See 'systemctl status [email protected]' for details.
[FAILED] Failed to start [email protected].
See 'systemctl status [email protected]' for details.
[FAILED] Failed to start [email protected].
See 'systemctl status [email protected]' for details.
[FAILED] Failed to start [email protected].
See 'systemctl status [email protected]' for details.
[FAILED] Failed to start [email protected].
See 'systemctl status [email protected]' for details.
[FAILED] Failed to start [email protected].
See 'systemctl status [email protected]' for details.
[FAILED] Failed to start [email protected].
See 'systemctl status [email protected]' for details.
[  OK  ] DietPi-Set_Hardware | Setting in /DietPi/config.txt adjusted: enable_uart=0
[  OK  ] serialconsole disable | Completed
[  OK  ] Root access verified.
[ INFO ] DietPi-Drive_Manager | Checking RootFS R/W access. Please wait...
[  OK  ] DietPi-Drive_Manager | RootFS R/W access.


 DietPi-Set_software
─────────────────────────────────────────────────────
 Mode: apt-mirror (http://mirror.netcologne.de/raspbian/raspbian/)

[  OK  ] apt-mirror http://mirror.netcologne.de/raspbian/raspbian/ | Completed
         Stopping Raise network interfaces...
[  OK  ] Stopped Raise network interfaces.
dhclient: no process found
Internet Systems Consortium DHCP Client 4.3.5
Copyright 2004-2016 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/eth0/00:e0:4c:53:44:58
Sending on   LPF/eth0/00:e0:4c:53:44:58
Sending on   Socket/fallback
DHCPREQUEST of 192.168.0.104 on eth0 to 255.255.255.255 port 67
DHCPREQUEST of 192.168.0.104 on eth0 to 255.255.255.255 port 67
[ TIME ] Timed out waiting for device dev-ttySAC2.device.
[ TIME ] Timed out waiting for device dev-tty.device.
[ TIME ] Timed out waiting for device dev-ttyAMA1.device.
[ TIME ] Timed out waiting for device dev-ttyS1.device.
[ TIME ] Timed out waiting for device dev-ttyS2.device.
[ TIME ] Timed out waiting for device dev-ttySAC0.device.
[ TIME ] Timed out waiting for device dev-ttyAMA2.device.
[ TIME ] Timed out waiting for device dev-ttySAC1.device.
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 3

...

[Fourdee]

@k-plan

Legend, thanks for testing.

[FAILED]

I'll check this, see if we can resolve, then redo the image and set live.

[Fourdee]

New image live, not had a chance to check out the reported serial errors yet.

Notes:
RPi disable those? uses kernel cmd line options and ignore service?

[Fourdee]

Couldn't replicate this in my testing:

[ TIME ] Timed out waiting for device dev-ttySAC2.device.

root@DietPi:~# /DietPi/dietpi/func/dietpi-set_hardware serialconsole disable
[  OK  ] Root access verified.
[  OK  ] DietPi-Drive_Manager | RootFS R/W access verified.


 DietPi-Set_Hardware
─────────────────────────────────────────────────────
 Mode: serialconsole (disable)

[ INFO ] DietPi-Set_Hardware | Disabling known serial-getty services, please wait...
[  OK  ] DietPi-Set_Hardware | Setting in /DietPi/config.txt adjusted: enable_uart=0
[  OK  ] serialconsole disable | Completed

Appears the issue is now resolved. I'll mark this as completed.