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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/
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