Compress kernels with gzip

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 
 - Replaced rotary encoder routines with a much more robust algorithm borrowed from [FlashFloppy](https://github.com/keirf/flashfloppy).
+- Kernels are now gzip-compressed, which saves some SD card space and may slightly reduce loading times.
 
 ### Fixed
 

Config.mk

@@ -14,6 +14,9 @@ USERBAUD?=115200
 # Enable section garbage collection
 GC_SECTIONS?=1
 
+# Compress the kernel
+GZIP_KERNEL?=1
+
 # Toolchain setup
 ifeq ($(BOARD), pi2)
 RASPBERRYPI=2

Makefile

@@ -44,6 +44,7 @@ $(CIRCLE_STDLIB_CONFIG) $(CIRCLE_CONFIG)&:
 # Apply patches
 	@${APPLY_PATCH} $(CIRCLEHOME) patches/circle-45-minimal-usb-drivers.patch
 	@${APPLY_PATCH} $(CIRCLEHOME) patches/circle-45-cp210x-remove-partnum-check.patch
+	@${APPLY_PATCH} $(CIRCLEHOME) patches/circle-45-gzip-kernel.patch
 
 ifeq ($(strip $(GC_SECTIONS)),1)
 # Enable function/data sections for circle-stdlib
@@ -148,6 +149,7 @@ clean:
 #
 mrproper: clean
 # Reverse patches
+	@${REVERSE_PATCH} $(CIRCLEHOME) patches/circle-45-gzip-kernel.patch
 	@${REVERSE_PATCH} $(CIRCLEHOME) patches/circle-45-cp210x-remove-partnum-check.patch
 	@${REVERSE_PATCH} $(CIRCLEHOME) patches/circle-45-minimal-usb-drivers.patch
 	@${REVERSE_PATCH} $(FLUIDSYNTHHOME) patches/fluidsynth-2.3.1-circle.patch

patches/circle-45-gzip-kernel.patch

@@ -0,0 +1,42 @@
+From 596544ca81def86971281594720f22524e7b563d Mon Sep 17 00:00:00 2001
+From: Dale Whinham <daleyo@gmail.com>
+Date: Sun, 5 Mar 2023 18:22:55 +0000
+Subject: [PATCH] Rules.mk: Add option to gzip-compress the kernel
+
+The Raspberry Pi bootloader is capable of booting kernels compressed
+with gzip. This can help improve startup times with larger kernels
+containing static data.
+
+Allow the user to define GZIP_KERNEL = 1 so that the final kernel image
+is replaced with a gzip-compressed file.
+---
+ Rules.mk | 9 +++++++++
+ 1 file changed, 9 insertions(+)
+
+diff --git a/Rules.mk b/Rules.mk
+index 9f23e7f0..9880488f 100644
+--- a/Rules.mk
++++ b/Rules.mk
+@@ -50,6 +50,9 @@ FLOAT_ABI ?= hard
+ # set this to 1 to enable garbage collection on sections, may cause side effects
+ GC_SECTIONS ?= 0
+ 
++# set this to 1 to gzip-compress the kernel
++GZIP_KERNEL ?= 0
++
+ ifneq ($(strip $(CLANG)),1)
+ CC	= $(PREFIX)gcc
+ CPP	= $(PREFIX)g++
+@@ -215,6 +218,12 @@ endif
+ 	@$(OBJCOPY) $(TARGET).elf -O binary $(TARGET).img
+ 	@echo -n "  WC    $(TARGET).img => "
+ 	@wc -c < $(TARGET).img
++ifeq ($(strip $(GZIP_KERNEL)),1)
++	@gzip -9 -f -n $(TARGET).img
++	@mv $(TARGET).img.gz $(TARGET).img
++	@echo -n "  GZIP  $(TARGET).img => "
++	@wc -c < $(TARGET).img
++endif
+ 
+ clean:
+ 	@echo "  CLEAN " `pwd`