shift/rpi4_eufi_booting_flatcar.md

## rpi4_eufi_booting_flatcar.md

      
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              rpi4_eufi_booting_flatcar.md
            
          
    UEFI/iPXE booting Raspberry Pi for Flatcar Linux

Download and compile the following https://github.com/pftf/RPi4.git. I made the following change to edk2-platforms to always enable 3GB RAM+ as TFTP booting this seems to cause issues with it remembering the options.
diff --git a/Platform/RaspberryPi/RPi4/RPi4.dsc b/Platform/RaspberryPi/RPi4/RPi4.dsc
index c481c35342..4b495b1fe8 100644
--- a/Platform/RaspberryPi/RPi4/RPi4.dsc
+++ b/Platform/RaspberryPi/RPi4/RPi4.dsc
@@ -495,7 +495,7 @@
   # Supporting > 3GB of memory.
   #
   gRaspberryPiTokenSpaceGuid.PcdRamMoreThan3GB|L"RamMoreThan3GB"|gConfigDxeFormSetGuid|0x0|0
-  gRaspberryPiTokenSpaceGuid.PcdRamLimitTo3GB|L"RamLimitTo3GB"|gConfigDxeFormSetGuid|0x0|1
+  gRaspberryPiTokenSpaceGuid.PcdRamLimitTo3GB|L"RamLimitTo3GB"|gConfigDxeFormSetGuid|0x0|0
 
   #
   # Device Tree and ACPI selection.

Grab the RPI_EFI.fd, Shell.efi, UiApp.efi files from the Build/RPi4/RELEASE_GCC5/FV/ directory.
Download https://github.com/raspberrypi/firmware/raw/master/boot/{start4.elf,bcm2711-rpi-4-b.dtb,overlays/miniuart-bt.dtbo}
Create a config.txt with the following
arm_64bit=1
enable_uart=1
uart_2ndstage=1
enable_gic=1
armstub=RPI_EFI.fd
disable_commandline_tags=1
disable_overscan=1
device_tree_address=0x1f0000
device_tree_end=0x200000
dtoverlay=miniuart-bt

Compile iPXE for ARM64 and embed the following ipxe script into it
#!ipxe
# see https://ipxe.org/docs
# see https://ipxe.org/settings

# show the system information.
# NB you can run "config" to interactively see all the possible variables.
echo Platform..... ${platform}
echo Architecture. ${buildarch}
echo Product...... ${smbios/product}
echo Manufacturer. ${smbios/manufacturer}
echo Asset........ ${smbios/asset}
echo UUID......... ${smbios/uuid}
echo Serial....... ${smbios/serial}

# show the available network interfaces.
echo Network interfaces:
ifstat

echo Configuring net0 ${net0/mac} (${net0/chip}) from dhcp...
:retry_ifconf
ifconf --configurator dhcp net0 || goto retry_ifconf
echo MAC address.. ${net0/mac}
echo IP address... ${net0/ip}
echo Subnet mask.. ${net0/netmask}
echo Gateway...... ${net0/gateway}
echo DNS.......... ${net0/dns}
echo Hostname..... ${hostname}
echo Domain....... ${domain}
echo Next Server.. ${next-server}
echo Filename..... ${filename}

# we need to set the time from ntp because the pi does not have an rtc.
# NB having the correct time is a requirement to use TLS.
echo Getting the current time from ntp...
:retry_ntp
ntp pool.ntp.org || goto retry_ntp
echo Unix Time.... ${unixtime}

chain --autofree tftp://${next-server}/${filename}

Create pxelinux with the following
#!ipxe
## Flatcar Linux
#set base-url http://alpha.release.flatcar-linux.net/arm64-usr/current
set base-url http://192.168.1.94
kernel ${base-url}/flatcar_production_pxe.vmlinuz initrd=flatcar_production_pxe_image.cpio.gz flatcar.first_boot=1 initrd ${base-url}/flatcar_production_pxe_image.cpio.gz
boot

Or modify it redirect to your matchbox server.
Place the efi files onto an sdcard formatted FAT, I got the smallest SD cards I could find as the data is less than 1MB.
And the other files onto your tftp server.
I was unable to find a way to iPXE boot without the sdcard for the EFI files, this is probably possable, let me know if you find a way of doing it.