Modifying the MIPS Creator CI20 default u-boot environment

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Modifying the MIPS Creator CI20 default u-boot environment

Follow-up to https://gist.github.com/cellularmitosis/a79c663f2e8430bc58bab61d459c9c1b

This script is an example of building u-boot while modifying its default environment and flashing u-boot to an SD card.

In particular:

• the serial console baud rate is reduced to 9600 (to allow for flaky cabling)
• a maxcpus=1 kernel parameter is added (for stability)

Note: this script does not modify the ext4 rootfs partition created by the script in my previous post.

flash-ci20-uboot.sh

#!/bin/bash

# build and write u-boot to the CI20's SD card.
# note: this script does not touch the ext4 rootfs partition.

set -e -o pipefail
set -x

if test -z "$1" ; then
    echo "Error: no SD card device node specified." >&2
    echo "Usage: $0 <SD card device, e.g. /dev/sdc>" >&2
    exit 1
fi
device="$1"

which mipsel-linux-gnu-gcc >/dev/null 2>&1 || sudo apt-get install gcc-mipsel-linux-gnu

# the official CI20 u-boot fork
# UBOOT_REPO=${UBOOT_REPO:="https://github.com/MIPS/CI20_u-boot"}
# UBOOT_BRANCH=${UBOOT_BRANCH:="ci20-v2013.10"}

# Gabriele Svelto's u-boot fork with RAM timing fixes.
UBOOT_REPO=${UBOOT_REPO:="https://github.com/gabrielesvelto/CI20_u-boot"}
UBOOT_BRANCH=${UBOOT_BRANCH:="fixed-timings"}

# clone u-boot
cd /tmp
if ! test -e CI20_u-boot/Makefile ; then
    git clone "$UBOOT_REPO" -b "$UBOOT_BRANCH" --depth 1
fi

# reset u-boot from any previous build
cd /tmp/CI20_u-boot
make distclean
git reset --hard HEAD
git checkout "$UBOOT_BRANCH"

# change the cserial console baud rate to 9600
sed -i'' -e 's|console=ttyS4,115200 console=tty0 |console=ttyS4,9600 console=tty0,9600 |' /tmp/CI20_u-boot/include/configs/ci20.h

# disable the second CPU core for stability
# see https://groups.google.com/g/mips-creator-ci20/c/VXr7feU5XWA/m/rZjFYhjrAwAJ
sed -i'' -e 's|rootwait quiet rw|rootwait quiet maxcpus=1 rw|' /tmp/CI20_u-boot/include/configs/ci20.h

# build u-boot
CROSS_COMPILE=mipsel-linux-gnu- make -j4 ARCH=mips ci20_mmc
maxsize=14336
cursize=$(cat spl/u-boot-spl.bin | wc -c)
# JZ4780 internal boot ROM reads 14KB (14336 bytes) of data from the boot device
if test $cursize -ge $maxsize ; then
    echo "Error: spl/u-boot-spl.bin exceeds '$maxsize' bytes" >&2
    exit 1
fi

# note: the dd offsets below appear to come from the following buildroot config:
# https://github.com/buildroot/buildroot/blob/master/board/ci20/genimage.cfg
# image sdcard.img {
#     hdimage {
#     }
#     partition uboot-spl {
#         in-partition-table = "no"
#         image = "u-boot-spl.bin"
#         offset = 512
#     }
#     partition uboot {
#         in-partition-table = "no"
#         image = "u-boot.img"
#         offset = 14K
#     }
#     partition uboot-env {
#         in-partition-table = "no"
#         image = "uboot-env.bin"
#         offset = 526K
#     }
#     partition rootfs {
#         partition-type = 0x83
#         image = "rootfs.ext4"
#         offset = 2M
#     }
# }
# See also https://github.com/gabrielesvelto/CI20_u-boot/blob/ci20-v2013.10/include/configs/ci20.h

# wipe any saved u-boot environment
sudo dd if=/dev/zero of="$device" bs=1K seek=526 count=32 ; sync

# write the new u-boot
sudo dd if=spl/u-boot-spl.bin of="$device" obs=512 seek=1 ; sync
sudo dd if=u-boot.img of="$device" obs=1K seek=14 ; sync