Fix core clock speed, restore newer firmware

Fixes #292.

.github/workflows/ci.yml

@@ -99,23 +99,23 @@ jobs:
       with:
         submodules: recursive
 
-    # - name: Cache boot files
-    #   id: cache-boot-files
-    #   uses: actions/cache@v3
-    #   with:
-    #     path: |
-    #       sdcard/armstub8-rpi4.bin
-    #       sdcard/bcm2711-rpi-4-b.dtb
-    #       sdcard/bcm2711-rpi-400.dtb
-    #       sdcard/bcm2711-rpi-cm4.dtb
-    #       sdcard/bootcode.bin
-    #       sdcard/COPYING.linux
-    #       sdcard/fixup_cd.dat
-    #       sdcard/fixup4cd.dat
-    #       sdcard/LICENCE.broadcom
-    #       sdcard/start_cd.elf
-    #       sdcard/start4cd.elf
-    #     key: cache-boot-files-${{ hashFiles(join(env.boot-home, '/Makefile')) }}
+    - name: Cache boot files
+      id: cache-boot-files
+      uses: actions/cache@v3
+      with:
+        path: |
+          sdcard/armstub8-rpi4.bin
+          sdcard/bcm2711-rpi-4-b.dtb
+          sdcard/bcm2711-rpi-400.dtb
+          sdcard/bcm2711-rpi-cm4.dtb
+          sdcard/bootcode.bin
+          sdcard/COPYING.linux
+          sdcard/fixup_cd.dat
+          sdcard/fixup4cd.dat
+          sdcard/LICENCE.broadcom
+          sdcard/start_cd.elf
+          sdcard/start4cd.elf
+        key: cache-boot-files-${{ hashFiles(join(env.boot-home, '/Makefile')) }}
 
     - name: Cache WLAN firmware
       id: cache-wlan-firmware
@@ -134,17 +134,15 @@ jobs:
         key: cache-arm-toolchains-${{ env.toolchain-version }}
 
     - name: Update PATH
-      # if: steps.cache-boot-files.outputs.cache-hit != 'true'
+      if: steps.cache-boot-files.outputs.cache-hit != 'true'
       run: |
         for triplet in arm-none-eabi aarch64-none-elf; do
           echo "$HOME/gcc-arm-${{ env.toolchain-version }}-x86_64-${triplet}/bin" >> $GITHUB_PATH
         done
 
     - name: Download boot files and build ARM stub if not retrieved from cache
-      # if: steps.cache-boot-files.outputs.cache-hit != 'true'
-      # Temporarily patch boot firmware version
+      if: steps.cache-boot-files.outputs.cache-hit != 'true'
       run: |
-        patch -N -p1 --no-backup-if-mismatch -r - -d external/circle-stdlib/libs/circle < patches/circle-44.5-revert-firmware.patch
         make -C ${{ env.boot-home }} firmware armstub64
         cp  ${{ env.boot-home }}/armstub8-rpi4.bin \
             ${{ env.boot-home }}/bcm2711-rpi-4-b.dtb \

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Incorrect I²C clock speed with recent Raspberry Pi firmware versions (issue #292). This was caused by core clock frequency scaling by the GPU firmware. Changes to `config.txt` have been added to ensure the I²C clock is stable by locking the core frequency to 250MHz. The newer Raspberry Pi firmware has been restored.
+
 ## [0.12.1] - 2022-06-14
 
 ### Fixed

Makefile

@@ -16,7 +16,6 @@ $(CIRCLE_STDLIB_CONFIG) $(CIRCLE_CONFIG)&:
 	$(CIRCLESTDLIBHOME)/configure --raspberrypi=$(RASPBERRYPI) --prefix=$(PREFIX)
 
 	# Apply patches
-	@patch -N -p1 --no-backup-if-mismatch -r - -d $(CIRCLEHOME) < patches/circle-44.5-revert-firmware.patch
 	@patch -N -p1 --no-backup-if-mismatch -r - -d $(CIRCLEHOME) < patches/circle-44.4-minimal-usb-drivers.patch
 
 ifeq ($(strip $(GC_SECTIONS)),1)
@@ -122,7 +121,6 @@ clean:
 veryclean: clean
 	# Reverse patches
 	@patch -R -N -p1 --no-backup-if-mismatch -r - -d $(CIRCLEHOME) < patches/circle-44.4-minimal-usb-drivers.patch
-	@patch -R -N -p1 --no-backup-if-mismatch -r - -d $(CIRCLEHOME) < patches/circle-44.5-revert-firmware.patch
 	@patch -R -N -p1 --no-backup-if-mismatch -r - -d $(FLUIDSYNTHHOME) < patches/fluidsynth-2.2.7-circle.patch
 
 	# Clean circle-stdlib

patches/circle-44.5-revert-firmware.patch

@@ -1,13 +0,0 @@
-diff --git a/boot/Makefile b/boot/Makefile
-index 6aadb4b..90395d4 100644
---- a/boot/Makefile
-+++ b/boot/Makefile
-@@ -9,7 +9,7 @@
- #FIRMWARE = master
- 
- # Use firmware revision built/committed on: Mar 24 2022
--FIRMWARE ?= ea4c803c57697aad951a27fcd64c01ef16f9fe7f
-+FIRMWARE ?= 827fdd073638fa7b7292d1148fe0af7465111eae
- 
- BASEURL = https://github.com/raspberrypi/firmware/blob/$(FIRMWARE)/boot
- 

sdcard/config.txt

@@ -5,6 +5,10 @@ force_eeprom_read=0
 gpu_mem=16
 disable_overscan=1
 
+# Ensure stable I2C baud rate by locking the core clock
+core_freq=250
+core_freq_min=250
+
 # Uncomment the following line if your HDMI audio extractor isn't outputting any sound.
 # This forces HDMI signalling in case your device is detected as a DVI device.
 #hdmi_drive=2