README

In this directory you can download the Raspberry Pi firmware files, which are
required to boot a Circle kernel image on a Raspberry Pi computer. For 32-bit
operation (AArch32) on the Raspberry Pi 4 the configuration file config32.txt is
required, which is provided in this directory. For 64-bit operation (AArch64)
the configuration file config64.txt is required, which is provided here too. The
corresponding file has to be renamed to config.txt on the SD card. If you want
to use the FIQ on a Raspberry Pi 4, you need an additional Circle-specific ARM
stub file, which will be loaded by the firmware. This ARM stub can be built in
this directory.

FIRMWARE

To download the Raspberry Pi firmware files just enter in this directory:

	make

This will provide the following files:

	bootcode.bin		boot loader (not used on Raspberry Pi 4)
	start.elf		firmware executable for  Raspberry Pi 1-3
	start4.elf		firmware executable for  Raspberry Pi 4
	fixup.dat		relocation information for start.elf
	fixup4.dat		relocation information for start4.elf
	bcm2711-rpi-4-b.dtb	device tree binary needed for Raspberry Pi 4
	bcm2711-rpi-cm4.dtb	device tree binary needed for Compute Module 4
	LICENCE.broadcom	firmware license
	COPYING.linux		license for the device tree binaries
	start_cd.elf		cut-down firmware for Raspberry Pi 1-3 (option)
	start4cd.elf		cut-down firmware for Raspberry Pi 4 (option)
	fixup_cd.dat		relocation information for start_cd.elf (option)
	fixup4cd.dat		relocation information for start4cd.elf (option)

The cut-down version of the firmware is used, when the option "gpu_mem=16" is
specified in config.txt. It does not support codecs and 3D, but is smaller and
loads quicker. Without this option specified, the last four files are not
needed.

In any case you have to copy these files onto the first FAT partition on a SD
card along with the kernel*.img file of your Circle application.

For 32-bit operation (AArch32) on the Raspberry Pi 1-3 and Zero that's all. You
can put the SD card into you Raspberry Pi computer and power it on.

AARCH32 ON RASPBERRY PI 4 WITH FIQ

32-bit operation (AArch32) with FIQ (fast interrupt request) on the Raspberry Pi
4 requires an additional Circle-specific ARM stub file armstub7-rpi4.bin. This
file will be built when you enter the following command in this directory:

	make armstub

The build process uses the same toolchain, which is used to build Circle kernel
images. The toolchain prefix (PREFIX =) can be configured in the file
Config.mk in the Circle root directory. You have to copy the created file
armstub7-rpi4.bin to the SD card together with the other files (see above).

To tell the firmware, that the file armstub7-rpi4.bin has to be loaded, you have
to copy the configuration file config32.txt from this directory along with the
firmware files (see above) to the SD card. The file has to be renamed to
config.txt on the SD card.

AARCH64

For 64-bit operation (AArch64) use have to copy the configuration file
config64.txt from this directory additionally along with the firmware files (see
above) to the SD card. The file has to be renamed to config.txt on the SD card.

AARCH64 ON RASPBERRY PI 4 WITH FIQ

64-bit operation (AArch64) with FIQ (fast interrupt request) on the Raspberry Pi
4 requires an additional Circle-specific ARM stub file armstub8-rpi4.bin. This
file will be built when you enter the following command in this directory:

	make armstub64

The build process uses the same toolchain, which is used to build Circle kernel
images. The toolchain prefix (PREFIX64 =) can be configured in the file
Config.mk in the Circle root directory. You have to copy the created file
armstub8-rpi4.bin to the SD card together with the other files (see above).