Allwinner NAND flashing
=======================

A lot of Allwinner devices, especially the older ones (pre-H3 era),
comes with a NAND. NANDs storages are a pretty weak choice when it
comes to the reliability, and it comes with a number of flaws like
read and write disturbs, data retention issues, bloks becoming
unusable, etc.

In order to mitigate that, various strategies have been found to be
able to recover from those issues like ECC, hardware randomization,
and of course, redundancy for the critical parts.

This is obviously something that we will take into account when
creating our images. However, the BROM will use a quite weird pattern
when accessing the NAND, and will access only at most 4kB per page,
which means that we also have to split that binary accross several
pages.

In order to accomodate that, we create a tool that will generate an
SPL image that is ready to be programmed directly embedding the ECCs,
randomized, and with the necessary bits needed to reduce the number of
bitflips. The U-Boot build system, when configured for the NAND will
also generate the image sunxi-spl-with-ecc.bin that will have been
generated by that tool.

In order to flash your U-Boot image onto a board, assuming that the
board is in FEL mode, you'll need the sunxi-tools that you can find at
this repository: https://github.com/linux-sunxi/sunxi-tools

Then, you'll need to first load an SPL to initialise the RAM:
sunxi-fel spl spl/sunxi-spl.bin

Load the binaries we'll flash into RAM:
sunxi-fel write 0x4a000000 u-boot-dtb.bin
sunxi-fel write 0x43000000 spl/sunxi-spl-with-ecc.bin

And execute U-Boot
sunxi-fel exe 0x4a000000

On your board, you'll now have all the needed binaries into RAM, so
you only need to erase the NAND...

nand erase.chip

Then write the SPL and its backup:

nand write.raw.noverify 0x43000000 0 40
nand write.raw.noverify 0x43000000 0x400000 40

And finally write the U-Boot binary:
nand write 0x4a000000 0x800000 0xc0000

You can now reboot and enjoy your NAND.

Allwinner 64-bit boards README
==============================

Newer Allwinner SoCs feature ARMv8 cores (ARM Cortex-A53) with support for
both the 64-bit AArch64 mode and the ARMv7 compatible 32-bit AArch32 mode.
Examples are the Allwinner A64 (used for instance on the Pine64 board) or
the Allwinner H5 SoC (as used on the OrangePi PC 2).
These SoCs are wired to start in AArch32 mode on reset and execute 32-bit
code from the Boot ROM (BROM). As this has some implications on U-Boot, this
file describes how to make full use of the 64-bit capabilities.

Quick Start / Overview
======================
- Build the ARM Trusted Firmware binary (see "ARM Trusted Firmware (ATF)" below)
- Build U-Boot (see "SPL/U-Boot" below)
- Transfer to an uSD card (see "microSD card" below)
- Boot and enjoy!

Building the firmware
=====================

The Allwinner A64/H5 firmware consists of three parts: U-Boot's SPL, an
ARM Trusted Firmware (ATF) build and the U-Boot proper.
The SPL will load both ATF and U-Boot proper along with the right device
tree blob (.dtb) and will pass execution to ATF (in EL3), which in turn will
drop into the U-Boot proper (in EL2).
As the ATF binary will become part of the U-Boot image file, you will need
to build it first.

 ARM Trusted Firmware (ATF)
----------------------------
Checkout the "allwinner" branch from the github repository [1] and build it:
$ export CROSS_COMPILE=aarch64-linux-gnu-
$ make PLAT=sun50iw1p1 DEBUG=1 bl31
The resulting binary is build/sun50iw1p1/debug/bl31.bin. Either put the
location of this file into the BL31 environment variable or copy this to
the root of your U-Boot build directory (or create a symbolic link).
$ export BL31=/src/arm-trusted-firmware/build/sun50iw1p1/debug/bl31.bin
  (adjust the actual path accordingly)

If you run into size issues with the resulting U-Boot image file, it might
help to use a release build, by using "DEBUG=0" when building bl31.bin.
As sometimes the ATF build process is a bit picky about the toolchain used,
or if you can't be bothered with building ATF, there are known working
binaries in the firmware repository[3], purely for convenience reasons.

 SPL/U-Boot
------------
Both U-Boot proper and the SPL are using the 64-bit mode. As the boot ROM
enters the SPL still in AArch32 secure SVC mode, there is some shim code to
enter AArch64 very early. The rest of the SPL runs in AArch64 EL3.
U-Boot proper runs in EL2 and can load any AArch64 code (using the "go"
command), EFI applications (with "bootefi") or arm64 Linux kernel images
(often named "Image"), using the "booti" command.

$ make clean
$ export CROSS_COMPILE=aarch64-linux-gnu-
$ make pine64_plus_defconfig
$ make

This will build the SPL in spl/sunxi-spl.bin and a FIT image called u-boot.itb,
which contains the rest of the firmware.


Boot process
============
The on-die BROM code will try several methods to load and execute the firmware.
On a typical board like the Pine64 this will result in the following boot order:

1) Reading 32KB from sector 16 (@8K) of the microSD card to SRAM A1. If the
BROM finds the magic "eGON" header in the first bytes, it will execute that
code. If not (no SD card at all or invalid magic), it will:
2) Try to read 32KB from sector 16 (@8K) of memory connected to the MMC2
controller, typically an on-board eMMC chip. If there is no eMMC or it does
not contain a valid boot header, it will:
3) Initialize the SPI0 controller and try to access a NOR flash connected to
it (using the CS0 pin). If a flash chip is found, the BROM will load the
first 32KB (from offset 0) into SRAM A1. Now it checks for the magic eGON
header and checksum and will execute the code upon finding it. If not, it will:
4) Initialize the USB OTG controller and will wait for a host to connect to
it, speaking the Allwinner proprietary (but deciphered) "FEL" USB protocol.


To boot the Pine64 board, you can use U-Boot and any of the described methods.

FEL boot (USB OTG)
------------------
FEL is the name of the Allwinner defined USB boot protocol built in the
mask ROM of most Allwinner SoCs. It allows to bootstrap a board solely
by using the USB-OTG interface and a host port on another computer.
As the FEL mode is controlled by the boot ROM, it expects to be running in
AArch32. For now the AArch64 SPL cannot properly return into FEL mode, so the
feature is disabled in the configuration at the moment.

microSD card
------------
Transfer the SPL and the U-Boot FIT image directly to an uSD card:
# dd if=spl/sunxi-spl.bin of=/dev/sdx bs=8k seek=1
# dd if=u-boot.itb of=/dev/sdx bs=8k seek=5
# sync
(replace /dev/sdx with you SD card device file name, which could be
/dev/mmcblk[x] as well).

Alternatively you can use the SPL and the U-Boot FIT image combined into a
single file and transfer that instead:
# dd if=u-boot-sunxi-with-spl.bin of=/dev/sdx bs=8k seek=1

You can partition the microSD card, but leave the first MB unallocated (most
partitioning tools will do this anyway).

NOR flash
---------
Some boards (like the SoPine, Pinebook or the OrangePi PC2) come with a
soldered SPI NOR flash chip. On other boards like the Pine64 such a chip
can be connected to the SPI0/CS0 pins on the PI-2 headers.
Create the SPL and FIT image like described above for the SD card.
Now connect either an "A to A" USB cable to the upper USB port on the Pine64
or get an adaptor and use a regular A-microB cable connected to it. Other
boards often have a proper micro-B USB socket connected to the USB OTB port.
Remove a microSD card from the slot and power on the board.
On your host computer download and build the sunxi-tools package[2], then
use "sunxi-fel" to access the board:
$ ./sunxi-fel ver -v -p
This should give you an output starting with: AWUSBFEX soc=00001689(A64) ...
Now use the sunxi-fel tool to write to the NOR flash:
$ ./sunxi-fel spiflash-write 0 spl/sunxi-spl.bin
$ ./sunxi-fel spiflash-write 32768 u-boot.itb
Now boot the board without an SD card inserted and you should see the
U-Boot prompt on the serial console.

(Legacy) boot0 method
---------------------
boot0 is Allwiner's secondary program loader and it can be used as some kind
of SPL replacement to get U-Boot up and running from an microSD card.
For some time using boot0 was the only option to get the Pine64 booted.
With working DRAM init code in U-Boot's SPL this is no longer necessary,
but this method is described here for the sake of completeness.
Please note that this method works only with the boot0 files shipped with
A64 based boards, the H5 uses an incompatible layout which is not supported
by this method.

The boot0 binary is a 32 KByte blob and contained in the official Pine64 images
distributed by Pine64 or Allwinner. It can be easily extracted from a micro
SD card or an image file:
# dd if=/dev/sd<x> of=boot0.bin bs=8k skip=1 count=4
where /dev/sd<x> is the device name of the uSD card or the name of the image
file. Apparently Allwinner allows re-distribution of this proprietary code
"as-is".
This boot0 blob takes care of DRAM initialisation and loads the remaining
firmware parts, then switches the core into AArch64 mode.
The original boot0 code looks for U-Boot at a certain place on an uSD card
(at 19096 KB), also it expects a header with magic bytes and a checksum.
There is a tool called boot0img[3] which takes a boot0.bin image and a compiled
U-Boot binary (plus other binaries) and will populate that header accordingly.
To make space for the magic header, the pine64_plus_defconfig will make sure
there is sufficient space at the beginning of the U-Boot binary.
boot0img will also take care of putting the different binaries at the right
places on the uSD card and works around unused, but mandatory parts by using
trampoline code. See the output of "boot0img -h" for more information.
boot0img can also patch boot0 to avoid loading U-Boot from 19MB, instead
fetching it from just behind the boot0 binary (-B option).
$ ./boot0img -o firmware.img -B boot0.img -u u-boot-dtb.bin -e -s bl31.bin \
-a 0x44008 -d trampoline64:0x44000
Then write this image to a microSD card, replacing /dev/sdx with the right
device file (see above):
$ dd if=firmware.img of=/dev/sdx bs=8k seek=1

[1] https://github.com/apritzel/arm-trusted-firmware.git
[2] git://github.com/linux-sunxi/sunxi-tools.git
[3] https://github.com/apritzel/pine64/