These options specify the firmware files transferred to the Videocore GPU prior to booting.

`start_file` specifies the Videocore (VC4) firmware file to use.

`fixup_file` specifies the file used to fix up memory locations used in the `start_file` to match the GPU memory split. Note that the `start_file` and the `fixup_file` are a matched pair - using unmatched files will stop the board from booting. This is an advanced option, so we advise that you use `start_x` and `start_debug` rather than this option.

These provide a shortcut to some alternative `start_file` and `fixup_file` settings, and are the recommended methods for selecting firmware configurations.

`start_x=1` should be specified when using the camera module. Enabling the camera via `raspi-config` will set this automatically.

Set the `disable_commandline_tags` command to `1` to stop `start.elf` from filling in ATAGS (memory from `0x100`) before launching the kernel.

`cmdline` is the alternative filename on the boot partition from which to read the kernel command line string; the default value is `cmdline.txt`.

`kernel` is the alternative filename on the boot partition to use when loading the kernel. The default value on the Pi 1, Pi Zero, and Compute Module is `kernel.img`, and on the Pi 2, Pi 3, and Compute Module 3 it is `kernel7.img`. If `kernel8.img` is present on the Pi 3 or Compute Module 3, it will be loaded in preference and entered in 64-bit mode.

`kernel_address` is the memory address to which the kernel image should be loaded. 32-bit kernels are loaded to address `0x8000` by default, and 64-bit kernels to address `0x80000`. If `kernel_old` is set, kernels are loaded to the address `0x0`.

Set `kernel_old` to `1` to load the kernel to the memory address `0x0`.

`ramfsfile` is the optional filename on the boot partition of a ramfs to load. More information is available [here](https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=10532).

`ramfsaddr` is the memory address to which the `ramfsfile` should be loaded.

The `initramfs` command specifies both the ramfs filename **and** the memory address to which to load it. It performs the actions of both `ramfsfile` and `ramfsaddr` in one parameter. Example values are: `initramfs initramf.gz 0x00800000`. **NOTE:** This option uses different syntax from all the other options, and you should not use a `=` character here.

`init_uart_baud` is the initial UART baud rate. The default value is `115200`.

`init_uart_clock` is the initial UART clock frequency. The default value is `48000000` (48MHz). Note that this clock only applies to UART0 (ttyAMA0 in Linux), and that the maximum baudrate for the UART is limited to 1/16th of the clock. The default UART on the Pi 3 and Pi Zero is UART1 (ttyS0 in Linux), and its clock is the core VPU clock - at least 250MHz.

The `bootcode_delay` command delays for a given number of seconds in `bootcode.bin` before loading `start.elf`: the default value is `0`.

This is particularly useful to insert a delay before reading the EDID of the monitor, for example if the Pi and monitor are powered from the same source, but the monitor takes longer to start up than the Pi. Try setting this value if the display detection is wrong on initial boot, but is correct if you soft-reboot the Pi without removing power from the monitor.

The `boot_delay` command instructs to wait for a given number of seconds in `start.elf` before loading the kernel: the default value is `1`. The total delay in milliseconds is calculated as `(1000 x boot_delay) + boot_delay_ms`. This can be useful if your SD card needs a while to get ready before Linux is able to boot from it.

The `boot_delay_ms` command means wait for a given number of milliseconds in `start.elf`, together with `boot_delay`, before loading the kernel. The default value is `0`.

If `disable_splash` is set to `1`, the rainbow splash screen will not be shown on boot. The default value is `0`.