2018-06-05 20:34:03 +02:00
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BOOTBOOT Raspberry Pi 3 Implementation
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======================================
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See [BOOTBOOT Protocol](https://gitlab.com/bztsrc/bootboot) for common details.
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On [Raspberry Pi 3](https://www.raspberrypi.org/documentation/hardware/raspberrypi/bootmodes/sdcard.md) board the bootboot.img
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is loaded from the boot (or firmware) partition on SD card as kernel8.img by start.elf. For separating firmware and boot
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partitions see [documentation](https://gitlab.com/bztsrc/bootboot/blob/master/bootboot_spec_1st_ed.pdf).
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Machine state
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-------------
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In addition to standard mappings, the MMIO is also mapped in kernel space:
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```
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-128M MMIO (0xFFFFFFFFF8000000)
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```
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Code is running in supervisor mode, at EL1. Dummy exception handlers are installed, but your kernel should use it's own
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handlers as soon as possible.
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File system drivers
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-------------------
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For boot partition, RPi3 version expects FAT16 or FAT32 file systems (if the
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initrd is a file and does not occupy the whole boot partition). The initrd can also be loaded over serial line,
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running [raspbootcom](https://gitlab.com/bztsrc/bootboot/blob/master/aarch64-rpi/raspbootcom.c) on a remote machine.
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Gzip compression is not recommended as reading from SD card is considerably faster than uncompressing.
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Installation
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------------
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1. Copy __bootboot.img__ to **_FS0:\KERNEL8.IMG_**.
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2. You'll need other [firmware files](https://gitlab.com/raspberrypi/firmware/tree/master/boot) as well.
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3. If you have used a GPT disk with ESP as boot partition, then you need to map it in MBR so that Raspberry Pi
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firmware could find those files. The [mkboot](https://gitlab.com/bztsrc/bootboot/blob/master/aarch64-rpi/mkboot.c)
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utility will do that for you.
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Limitations
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-----------
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- Initrd in ROM is not possible
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- Maps only the first 1G of RAM.
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- Cards other than SDHC Class 10 not supported.
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- Raspberry Pi does not have an on-board RTC, so always 0000-00-00 00:00:00 returned as bootboot.datetime.
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2018-11-09 12:43:03 +01:00
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- Only supports SHA-XOR-CBC cipher, no AES
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