86 lines
3.4 KiB
Bash
86 lines
3.4 KiB
Bash
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#!/usr/bin/env bash
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#
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# Install the Cuckoo Escapement PREEMPT_RT kernel on a Raspberry Pi 4.
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#
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# The design goal here is ONE THING: you must never need physical access to the
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# SD card because of something this script did. So:
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#
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# - kernel8.img (the stock kernel) is never touched
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# - the RT kernel installs under a NEW filename
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# - the ONLY change to config.txt is a single appended line
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#
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# If it doesn't boot: pull the card, open config.txt on any machine (it's a FAT
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# partition, so a Windows laptop will do), delete that one line, put it back.
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# The stock kernel returns. That's the entire rollback.
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#
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# Run it FROM the directory holding the release files.
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set -euo pipefail
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IMG_NAME="kernel-rt.img"
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BOOT="/boot/firmware"
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die() { printf '\nERROR: %s\n' "$1" >&2; exit 1; }
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[[ $EUID -eq 0 ]] || die "run with sudo"
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# --- Refuse to run on hardware this kernel was not built for. A bcm2711 kernel
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# --- on a Pi 5 does not boot, and the failure mode is a black screen on a
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# --- headless box, which is exactly what we promised wouldn't happen.
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MODEL="$(tr -d '\0' < /proc/device-tree/model 2>/dev/null || echo unknown)"
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case "$MODEL" in
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*"Raspberry Pi 4"*|*"Raspberry Pi Compute Module 4"*|*"Raspberry Pi 400"*) ;;
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*) die "this kernel is bcm2711 (Pi 4) only — found: $MODEL" ;;
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esac
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[[ "$(uname -m)" == "aarch64" ]] || die "need a 64-bit OS (uname -m says $(uname -m))"
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[[ -d "$BOOT" ]] || die "$BOOT not found — is this Raspberry Pi OS?"
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IMG_GZ="$(ls -1 kernel-rt-*.img.gz 2>/dev/null | head -1)" || true
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MODS="$(ls -1 rt-modules-*.tar.gz 2>/dev/null | head -1)" || true
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[[ -n "${IMG_GZ:-}" && -n "${MODS:-}" ]] || die "run this from the directory containing the release files"
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# --- The image and the modules MUST come from the same build. A mismatched pair
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# --- means modprobe fails on vermagic — and since pps-gpio is a module, that
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# --- means no /dev/pps0 and no refclock, on a kernel that otherwise boots fine.
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# --- Silent, and miserable to debug. Check it up front.
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IMG_VER="${IMG_GZ#kernel-rt-}"; IMG_VER="${IMG_VER%.img.gz}"
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MOD_VER="${MODS#rt-modules-}"; MOD_VER="${MOD_VER%.tar.gz}"
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[[ "$IMG_VER" == "$MOD_VER" ]] \
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|| die "image ($IMG_VER) and modules ($MOD_VER) are from different builds"
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if [[ -f SHA256SUMS ]]; then
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echo "==> verifying checksums"
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sha256sum -c SHA256SUMS || die "checksum mismatch — do not install this"
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else
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echo "!! no SHA256SUMS present — skipping verification (not recommended)"
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fi
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echo "==> installing modules for $MOD_VER"
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tar -C / -xzf "$MODS"
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depmod -a "$MOD_VER"
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echo "==> installing kernel as $BOOT/$IMG_NAME (kernel8.img left alone)"
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zcat "$IMG_GZ" > "$BOOT/$IMG_NAME"
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if grep -qE "^kernel=$IMG_NAME" "$BOOT/config.txt"; then
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echo "==> config.txt already selects $IMG_NAME"
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else
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cp "$BOOT/config.txt" "$BOOT/config.txt.before-rt"
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printf '\n# Cuckoo Escapement RT kernel. DELETE THIS LINE to boot the stock kernel.\nkernel=%s\n' \
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"$IMG_NAME" >> "$BOOT/config.txt"
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echo "==> appended 'kernel=$IMG_NAME' to config.txt (backup: config.txt.before-rt)"
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fi
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cat <<EOF
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Done. Reboot, then confirm:
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uname -a # expect $MOD_VER ... SMP PREEMPT_RT
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ps -eo comm | grep irq/.*pps # expect NOTHING — the handler must not be
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# a thread. If you see one, the patch isn't
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# in this kernel and your jitter will be bad.
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To roll back: delete the 'kernel=$IMG_NAME' line from $BOOT/config.txt
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(or restore config.txt.before-rt) and reboot.
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EOF
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