Changing AllStar screen resolution

December 25, 2018

The Problem

I recently became interested in AllStarLink, and had a HamVoip image installed on a Raspberry Pi. (I was using “RPi2-3 includes 3B+ Image Version 1.5rc19”.)

The AllStarLink image booted to 1366×768, which was the screen’s default resolution. However, the screen itself was a 7 inch HDMI screen. That was hard to read.

Things that didn’t work

I decided to change the resolution by editing /boot/cmdline.txt. My first attempt was to add:

framebuffer_width=720
framebuffer_height=400

before the root= line at the beginning of the file. That resulted in a kernel panic:

Kernel Panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

After a while, I realized that root= had to come first. Then I tried:

root=/dev/mmcblk0p2 rw rootwait bcm2708_fb.fbwidth=720 bcm2708_fb.fbheight=400
console=ttyAMA0,115200 console=tty1 selinux=0 plymouth.enable=0
smsc95xx.turbo_mode=N dwc_otg.lpm_enable=0 kgdboc=ttyAMA0,115200 elevator=noop
hdmi_safe=1
hdmi_group=1
hdmi_mode=1

but my cmdline.txt values seemed to be ignored.

Finally I wised up: apparently when the Pi reads the root line it starts booting, ignoring everything after it in cmdline.txt. So, I had to pass the video size as a kernel parameter instead.

I did:

cat /proc/cmdline

and saw:

8250.nr_uarts=0 bcm2708_fb.fbwidth=1366 bcm2708_fb.fbheight=768
bcm2708_fb.fbswap=1 vc_mem.mem_base=0x3ec00000 vc_mem.mem_size=0x40000000
root=/dev/mmcblk0p2 rw rootwait console=ttyS0,115200 console=tty1 selinux=0
plymouth.enable=0 smsc95xx.turbo_mode=N dwc_otg.lpm_enable=0 kgdboc=ttyS0,115200 elevator=noop

The Solution

(For Linux / AllStarLink newbies: in order to get to the terminal, I picked menu item 9 – open a bash shell.)

I went into /boot/cmdline.txt with a text editor:

nano /boot/cmdline.txt

and inserted the following two parameters on the existing line that begins with “root=”:

bcm2708_fb.fbwidth=720 bcm2708_fb.fbheight=400

I put these right after the rootwait parameter, so in /boot/cmdline.txt I now had:

root=/dev/mmcblk0p2 rw rootwait bcm2708_fb.fbwidth=720 bcm2708_fb.fbheight=400
console=ttyAMA0,115200 console=tty1 selinux=0 plymouth.enable=0
smsc95xx.turbo_mode=N dwc_otg.lpm_enable=0 kgdboc=ttyAMA0,115200 elevator=noop

(Note that root line is all one long line – not broken up with line separators!)

Once I did that and saved it, the Raspberry Pi booted up in glorious 80×25 text. Now we could read it!

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