"druck"  wrote in message
news:riual9$93d$1@dont-email.me...
> On 04/09/2020 21:31, NY wrote:
>> I've got a Pi 3B+ and I'm thinking of upgrading to a 4B, partly to free
>> up the Pi 3 to do other tasks.
>>
>> I've got a couple of questions?
>>
>> - Can a "system disk" SD card (ie the same disk image) for 3B+ be used
>> for a 4B?
> As long as you've got the latest updates, you can just move the SD Card
> over.

"The latest updates" seems to be my stumbling block. I'd done "sudo apt
update" and "sudo apt full-upgrade" on the Pi 3B+ before imaging the card
and creating a copy onto a new cad for the Pi 4. But I still got

https://postimg.cc/ZWGp5pz7

recover4.elf not found
fixup_rc.dat not found
recovery.elf is not compatible

So I started again from scratch, installing from the latest NOOBS. I'm
tempted to try copying all the files from the new card's recovery partition
to the old card's, to see if it helps? But that would be to satisfy my
curiosity: since the new NOOBS comes with Raspbian Buster rather than
Stretch, I may as well use that.

I came across a couple of "funnies" as I was setting up the new Pi. The old
one was quite happy to boot without a monitor plugged in (I use my Pis
headless, accessed by VNC) whereas the new one wouldn't boot. The solution
is to add/modify a few lines in /boot/config.txt:

     hdmi_force_hotplug=1 # allow Pi to boot with no monitor connected
     hdmi_group=2
     hdmi_mode=82  # force 1920x1080x60 even though monitor can’t be
auto-detected

to allow the PI to boot with no monitor, and to force 1920x1080 mode for the
benefit of VNC.

Strangely, I couldn't get it to go into CEA mode 31 (1920x1080x50, rather
than 60) with

     hdmi_group=1
     hdmi_mode=31

because this still gave (according to my monitor, when I plugged it in) 60
Hz frame rate. But it doesn't really matter since the Pi will mostly be used
headless - apart from occasionally driving our telly when we want to browse
something - or to watch a webcam such as elephants in a safari park in Kenya
:-)

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