The Raspberry PI Foundation has released beta firmware and a bootloader to enable booting the Raspberry Pi 4 from a USB mass storage device.
The new firmware and bootloader could be useful to Raspberry Pi 4 owners who want the option of booting from a faster USB mass storage device instead of only doing so using an SD Card.
One of the feature highlights of the Raspberry Pi 4 Model B when it launched in June 2019 was USB 3.0, which enables faster storage than previous versions of the computer.
But, unlike previous models, the Raspberry Pi 4 didn't support USB mass storage boot, preventing users from installing an operating system from a USB mass storage device – a gap the foundation promised would be closed in a future software update.
That software update is nearly ready and for now is available in beta to use for those willing to accept bugs, failures, and errors in documentation.
"This is a beta release. If you aren't already comfortable with manual firmware updates then please wait until this is available in a standard release. It won't be very long," said Tim Gover, principal software engineer for Raspberry Pi Trading.
The reason the firmware update is required is due to a change in the design of the bootup procedure in the Raspberry Pi 4.
Instead of permanently burning the boot code into the ROM of the system on chip (SoC), Raspberry Pi 4's boot code is stored in SPI-attached electrically erasable programmable read-only memory (EEPROM), which can be updated.
Raspberry Pi also notes that because the USB moved to a PCIe bus and that there's a new Gigabit Ethernet driver, it wasn't feasible to have the boot code permanently fixed into the ROM.
Gover has offered instructions for booting from a USB storage card reader in an update on the page detailing the Raspberry Pi 4 bootloader.
"Initially we recommend using a USB pen drive or SSD. Hard drives will probably require a powered HUB and in all cases you should verify that the devices work correctly from within Raspbian using an SD card boot," Raspberry Pi Foundation notes.