RPi Firmware

In the Raspberry Pi architecture, it is the VC4 GPU that starts first and initialises the ARM processor and various peripherals in order for it to boot. In order to do this, it loads its firmware (in the normal case) from the SD card. Once it has initialised the ARM processor, it is started and it continues to load the Linux Kernel.

Each new model of Raspberry Pi contains different hardware. This could be as a result of fitting a new processor, more memory, or different peripherals such as wifi chips, bluetooth, ethernet or USB interfaces etc. In a few cases, the old firmware may be compatible, but in many cases, the new hardware requires different firmware in order to initialise the new processor, and new drivers in order for the Linux kernel to control the new peripherals.

In the case of the RPi 3B+, if old firmware is used on this model, it will be stuck on the square rainbow screen with the lightning symbol showing on the screen and one of the red or green LEDs flashing a repeated pattern of 4 short and 4 long flashes. In this case, the lightning symbol is NOT indicating a problem with the power supply, but a problem with the firmware.