102 lines
3.4 KiB
Markdown
102 lines
3.4 KiB
Markdown
---
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title: "Booting a Raspberry Pi Over TFTP"
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date: 2020-10-13T08:31:52-07:00
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draft: false
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series: ["Raspberry Pi OS Development"]
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categories: ["Tech"]
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tags: ["Raspberry Pi", "Networking"]
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---
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In order to do this, I modified the [EEPROM bootloader][eeprom] bootloader
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according to the instructions in the Raspberry Pi documentation. That page is
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also on [GitHub][eeprom-gh] which might be a more stable location. On Raspbian
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on the Raspberry Pi:
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{{< figures/code >}}
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```sh
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fw=/lib/firmware/raspberrypi/bootloader/stable/pieeprom-2020-09-03.bin
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rpi-eeprom-config $fw > ~/bootconf.txt
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vi ~/bootconf.txt
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rpi-eeprom-config --out ~/pieeprom-new.bin --config ~/bootconf.txt $fw
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sudo rpi-eeprom-update -d -f ~/pieeprom-new.bin
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sudo reboot
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```
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{{< /figures/code >}}
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My updated `bootconf.txt` is:
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{{< figures/code >}}
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```cfg
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[all]
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BOOT_UART=1
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WAKE_ON_GPIO=0
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POWER_OFF_ON_HALT=0
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DHCP_TIMEOUT=45000
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DHCP_REQ_TIMEOUT=4000
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TFTP_FILE_TIMEOUT=30000
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ENABLE_SELF_UPDATE=1
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DISABLE_HDMI=0
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BOOT_ORDER=0xf412
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```
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{{< /figures/code >}}
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I enabled UART debugging, and set the boot order to be: network `0x2`, SD card
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`0x1`, USB mass storage `0x4`, and finally reboot `0xf`. These steps need to be
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repeated if the bootloader is updated via apt.
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I [enabled the TFTP server][mac-tftp] on my Mac:
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{{< figures/code >}}
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```sh
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sudo launchctl load -F /System/Library/LaunchDaemons/tftp.plist
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sudo launchctl enable System/com.apple.tftpd
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sudo launchctl start com.apple.tftpd
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```
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{{< /figures/code >}}
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I’m not sure if the `enable` command is actually necessary. This doesn't
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actually start the `tftpd` daemon. Instead, macOS starts the daemon on demand
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when it notices an incoming tftp request on the network. Don't be alarmed!
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The tftp server looks for files to serve out of **`/private/tftpboot`**, and those
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things need to be world `rwx`, i.e. `777`. By default (this is configurable) the
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Raspberry Pi queries for a directory named by its serial number.
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{{< figures/code >}}
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```sh
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mkdir /private/tftpboot/$raspberry_pi_serial
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chmod 777 /private/tftpboot
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chmod -R 777 /private/tftpboot/*
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```
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{{< /figures/code >}}
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Raspberry Pi looks for files of various names in that directory, one in
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particular by the name of **`start.elf`**.
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Next, I had to update my Ubiquiti router's DHCP server configuration (on the
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command line) to pass a `tftp-server` parameter in the DHCP payload. This step
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may be optional because you can also set `TFTP_IP` in the **`bootconf.txt`** above
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to specify the IP directly. On my router:
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{{< figures/code >}}
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```sh
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configure
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set service dhcp-server shared-network-name LAN subnet $lan_cidr_subnet tftp-server-name $ip_of_mac
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commit
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save
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exit
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```
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{{< /figures/code >}}
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I also gave my Mac a static IP, and renewed the DHCP lease so it took the new IP
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to make the whole process a little more smooth. Now, it appears the Raspberry
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Pi will attempt a TFTP boot, and I see queries in the logs on my Mac.
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## Further Reading
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* [Hackaday's Raspberry Pi Boot Sequence Guide](https://hackaday.io/page/6372-raspberry-pi-4-boot-sequence)
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* [Linuxhit Guide to Booting a Raspberry Pi with PXE](https://linuxhit.com/raspberry-pi-pxe-boot-netbooting-a-pi-4-without-an-sd-card/)
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[eeprom]: https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2711_bootloader_config.md
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[eeprom-gh]: https://github.com/raspberrypi/documentation/blob/master/hardware/raspberrypi/bcm2711_bootloader_config.md
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[mac-tftp]: https://www.unixfu.ch/start-a-tftp-server-on-your-mac/
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