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Add 'Boot RaspPi over TFTP' post

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Eryn Wells 2021-10-05 08:51:44 -07:00
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---
title: "Booting a Raspberry Pi Over TFTP"
date: 2020-10-14T08:31:52-07:00
draft: true
series: ["Raspberry Pi OS Development"]
tags: ["Tech"]
---
In order to do this, I modified the [EEPROM bootloader][eeprom] bootloader
according to the instructions in the Raspberry Pi documentation. That page is
also on [GitHub][eeprom-gh] which might be a more stable location. On Raspbian
on the RPi:
```bash
fw=/lib/firmware/raspberrypi/bootloader/stable/pieeprom-2020-09-03.bin
rpi-eeprom-config $fw > ~/bootconf.txt
vi ~/bootconf.txt
rpi-eeprom-config --out ~/pieeprom-new.bin --config ~/bootconf.txt $fw
sudo rpi-eeprom-update -d -f ~/pieeprom-new.bin
sudo reboot
```
My updated bootconf.txt is:
```conf
[all]
BOOT_UART=1
WAKE_ON_GPIO=0
POWER_OFF_ON_HALT=0
DHCP_TIMEOUT=45000
DHCP_REQ_TIMEOUT=4000
TFTP_FILE_TIMEOUT=30000
ENABLE_SELF_UPDATE=1
DISABLE_HDMI=0
BOOT_ORDER=0xf412
```
I enabled UART debugging, and set the boot order to be: network `0x2`, SD card
`0x1`, USB mass storage `0x4`, and finally reboot `0xf`. These steps need to be
repeated if the bootloader is updated via apt.
I [enabled the TFTP server][mac-tftp] on my Mac:
```bash
sudo launchctl load -F /System/Library/LaunchDaemons/tftp.plist
sudo launchctl enable System/com.apple.tftpd
sudo launchctl start com.apple.tftpd
```
I’m not sure if the `enable` command is actually necessary. This doesn't
actually start the `tftpd` daemon. Instead, macOS starts the daemon on demand
when it notices an incoming tftp request on the network. Don't be alarmed!
The tftp server looks for files to serve out of **/private/tftpboot**, and those
things need to be world `rwx`, i.e. `777`. By default (this is configurable) the
RPi queries for a directory named by its serial number.
```bash
mkdir /private/tftpboot/fe4358ed
chmod 777 /private/tftpboot
chmod -R 777 /private/tftpboot/*
```
RPi looks for files of various names in that directory, one in particular by the
name of **start.elf**.
Next, I had to update my Ubiquiti router's DHCP server configuration (on the
command line) to pass a `tftp-server` parameter in the DHCP payload. This step
may be optional because you can also set `TFTP_IP` in the **bootconf.txt** above
to specify the IP directly. On my router:
```bash
configure
set service dhcp-server shared-network-name LAN subnet $lan_cidr_subnet tftp-server-name $ip_of_mac
commit
save
exit
```
I also gave my Mac a static IP, and renewed the DHCP lease so it took the new IP
to make the whole process a little more smooth. Now, it appears the RPi will
attempt a TFTP boot, and I see queries in the logs on my Mac.
## Further Reading
* [Hackaday's Raspberry Pi Boot Sequence Guide](https://hackaday.io/page/6372-raspberry-pi-4-boot-sequence)
* [Linuxhit Guide to Booting a Raspberry Pi with PXE](https://linuxhit.com/raspberry-pi-pxe-boot-netbooting-a-pi-4-without-an-sd-card/)
[eeprom]: https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2711_bootloader_config.md
[eeprom-gh]: https://github.com/raspberrypi/documentation/blob/master/hardware/raspberrypi/bcm2711_bootloader_config.md
[mac-tftp]: https://www.unixfu.ch/start-a-tftp-server-on-your-mac/