Ox64 proof of concept: boot NuttX from flash

nuttx_poc.sh

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# In this document, we outline the steps required to make a standalone flash
# image for the Ox64 that boots NuttX. We will be using the OpenBouffalo
# buildroot overlay to help us with this, but we will not be building the
# Linux kernel or rootfs.
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# We are using a patched OpenBouffalo overlay so that NuttX is loaded at
# 0x50200000 instead of 0x50000000. If you wish, you can build your own
# NuttX image whose memory map starts at 0x50000000, and then continue following
# these instructions using the upstream OpenBouffalo overlay instead.
git clone -b nuttx_poc https://github.com/Pavlos1/buildroot_bouffalo
git clone https://github.com/buildroot/buildroot

export BR_BOUFFALO_OVERLAY_PATH=$(pwd)/buildroot_bouffalo
cd buildroot
make BR2_EXTERNAL=$BR_BOUFFALO_OVERLAY_PATH pine64_ox64_defconfig

# Note: These are the same settings as you would set when building a regular
#       OpenBouffalo linux image.
make menuconfig
#    * Navigate to Target Options
#    * Enable Integer Multiplication and Division (M)
#    * Enable Atomic Instructions (A)
#    * Enable Single-precision Floating-point (F)
#    * Enable Double-precision Floating-point (D)
#    * Set Target ABI to lp64d
#    * Under Toolchain, enable Fortran support and OpenMP support

# Avoid building the whole system...
make opensbi uboot oblfr
cd output/images

# Download the NuttX image. You may replace it with your own if you wish, but
# make sure it still ends up at output/images/ImageNuttx
wget -O ImageNuttx https://github.com/lupyuen2/wip-pinephone-nuttx/releases/download/bl808d-1/Image

# Compress the NuttX image
lz4 ImageNuttx ImageNuttx.lz4

# Generate our equivalent of `bl808-firmware.bin`.
# Note: I don't think `u-boot.dtb` gets picked up by NuttX at all. It's just
#       here so that mergebin.py has something vaguely sensible to process.
$BR_BOUFFALO_OVERLAY_PATH/board/pine64/ox64/mergebin.py \
    -o bl808-nuttx.bin -k ImageNuttx.lz4 -d u-boot.dtb -s fw_jump.bin

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# File checklist (in output/images):
#   * m0_lowload_bl808_m0.bin
#   * d0_lowload_bl808_d0.bin
#   * bl808-nuttx.bin
#
# Flash these the same way you would flash normal OpenBouffalo images.
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