diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 31a94891..89a2a029 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -5,6 +5,10 @@ on:
     branches: ['**']
   pull_request:
 
+permissions:
+  contents: read
+  pull-requests: write
+
 jobs:
   build:
     runs-on: ubuntu-latest
@@ -13,18 +17,52 @@ jobs:
 
     steps:
       - uses: actions/checkout@v6
+        with:
+          path: branch
+
+      - uses: actions/checkout@v6
+        with:
+          path: main
+          ref: main
 
       - name: Install dependencies
         run: |
           apt update
           apt install make gcc sdcc xxd python-is-python3 libjson-c-dev zlib1g-dev -y
       - name: Run the host-side unit tests
-        run: make -C test
+        run: cd branch && make -C test
       - name: Check that every machine definition can be compiled
-        run: make machine_check
+        run: cd branch && make machine_check
       - name: Make project (4x2/RTL8372)
-        run: make CI=1 MACHINE="KP_9000_6XHML_X2"
+        run: cd branch && make CI=1 MACHINE="KP_9000_6XHML_X2" && cp output/KP_9000_6XHML_X2/rtlplayground.map /tmp/branch.map
       - name: Make project (8x1/RTL8373)
-        run: make CI=1 MACHINE="KP_9000_9XHML_X_V3_1"
+        run: cd branch && make CI=1 MACHINE="KP_9000_9XHML_X_V3_1"
       - name: Make project with the health instrumentation
-        run: make clean && make CI=1 MACHINE="KP_9000_6XHML_X2" HEALTH=1
+        run: cd branch && make clean && make CI=1 MACHINE="KP_9000_6XHML_X2" HEALTH=1
+      - name: Make main
+        run: cd main && make CI=1 MACHINE="KP_9000_6XHML_X2" && cp output/KP_9000_6XHML_X2/rtlplayground.map /tmp/main.map
+      - name: Calculate bank growth
+        run: |
+          sed -rn 's/^([XCD]SEG|(BANK[0-9])).*=\s+([0-9]+)\. bytes.*$/MAIN_\1=\3/p' /tmp/main.map | sort -u >> "$GITHUB_ENV"
+          sed -rn 's/^([XCD]SEG|(BANK[0-9])).*=\s+([0-9]+)\. bytes.*$/BRANCH_\1=\3/p' /tmp/branch.map | sort -u >> "$GITHUB_ENV"
+          du -sb main/output/html_min | awk '{print "MAIN_WEB="$1}' >> "$GITHUB_ENV"
+          du -sb branch/output/html_min | awk '{print "BRANCH_WEB="$1}' >>"$GITHUB_ENV"
+
+      - name: Update PR comment
+        uses: marocchino/sticky-pull-request-comment@v3
+        with:
+          header: Sizes
+          message: |
+            ## Image Growth
+
+            Commit: ${{ github.sha }}
+
+            | Name | Main | Branch |
+            | --- | --- | --- |
+            | XSEG | ${{ env.MAIN_XSEG }} bytes | ${{ env.BRANCH_XSEG }} bytes |
+            | CSEG | ${{ env.MAIN_CSEG }} bytes | ${{ env.BRANCH_CSEG }} bytes |
+            | DSEG | ${{ env.MAIN_DSEG }} bytes | ${{ env.BRANCH_DSEG }} bytes |
+            | 1 | ${{ env.MAIN_BANK1 }} bytes | ${{ env.BRANCH_BANK1 }} bytes |
+            | 2 | ${{ env.MAIN_BANK2 }} bytes | ${{ env.BRANCH_BANK2 }} bytes |
+            | 3 | ${{ env.MAIN_BANK3 }} bytes | ${{ env.BRANCH_BANK3 }} bytes |
+            | HTML/JS | ${{ env.MAIN_WEB }} bytes | ${{ env.BRANCH_WEB }} bytes |
\ No newline at end of file
diff --git a/.gitignore b/.gitignore
index 11f5c4ed..9f544835 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 .gitignore
 .idea/
 output/
+output-main/
 html_data.c
 html_data.h
 version.h
@@ -12,3 +13,4 @@ build/
 # host-test stand-ins for the two generated headers
 !test/stub/html_data.h
 !test/stub/version.h
+.vscode
diff --git a/Makefile b/Makefile
index c95f12af..54660495 100644
--- a/Makefile
+++ b/Makefile
@@ -34,7 +34,10 @@ endif
 # The board definition being built: one file per MACHINE_* symbol in machine.h.
 MACHINE_SRC = machine/$(MACHINE).c
 
-BUILDDIR = output/$(MACHINE)
+ifndef BUILDDIR
+	BUILDDIR = output/$(MACHINE)
+endif
+
 VERSION_HEADER := version.h
 
 GIT_VERSION := $(shell git rev-parse --short HEAD)
@@ -61,6 +64,9 @@ endif
 # is built, including the tools/ subdirectory.
 all: create_build_dir $(VERSION_HEADER) $(MACHINE_SRC) $(SUBDIRS) $(BUILDDIR)/rtlplayground-$(FILENAME_EXTENSION).bin
 
+bank_size:
+	tools/bank_occupancy.sh "$(MACHINE)"
+
 create_build_dir:
 	mkdir -p "$(BUILDDIR)"
 	mkdir -p "$(BUILDDIR)/uip"
@@ -133,7 +139,7 @@ HTML := $(shell find html -name '*.js' -or -name '*.html' -or -name '*.svg' -or
 # Minified copy of the web UI sources, used as the fileadder input.
 # The raw html/ sources stay untouched for development; the minified
 # copy is a build artifact under output/.
-HTML_MIN := output/html_min
+HTML_MIN := $(BUILDDIR)/html_min
 .PHONY: html_min
 html_min: $(HTML)
 	rm -rf $(HTML_MIN)
@@ -155,7 +161,7 @@ $(VERSION_HEADER): FORCE
 httpd: html_data.h
 
 $(SUBDIRS):
-	$(MAKE) -C $@
+	$(MAKE) -C $@ BUILDDIR=$(BUILDDIR)
 
 clean: $(SUBDIRSCLEAN)
 	-rm -f html_data.c html_data.h $(VERSION_HEADER)
@@ -198,7 +204,7 @@ $(BUILDDIR)/rtlplayground-$(FILENAME_EXTENSION).bin: $(BUILDDIR)/rtlplayground.i
 	tools/output/fileadder -a $(CONFIG_LOCATION) -s $(IMAGESIZE) -d config.txt $@
 	tools/output/fileadder -a $(HTML_LOCATION) -s $(IMAGESIZE) -z -d $(HTML_MIN) -b BANK1 $@
 	tools/output/crc_calculator -u $@
-	ln -sf $(MACHINE)/rtlplayground-$(FILENAME_EXTENSION).bin output/rtlplayground.bin
+	ln -sf $(MACHINE)/rtlplayground-$(FILENAME_EXTENSION).bin $(BUILDDIR)/../rtlplayground.bin
 
 .PHONY: clean distclean all $(SUBDIRS) $(SUBDIRSCLEAN) create_build_dir
 
diff --git a/tools/Makefile b/tools/Makefile
index 1b1c6685..80ac9743 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -1,6 +1,8 @@
 CC = gcc
 CCFLAGS = -Wall -o
-BUILDDIR = output
+ifndef BUILDDIR
+	BUILDDIR = output
+endif
 
 all: create_build_dir $(BUILDDIR)/injector $(BUILDDIR)/fileadder $(BUILDDIR)/httpd_sim\
 	$(BUILDDIR)/crc_calculator $(BUILDDIR)/imagebuilder
diff --git a/tools/bank_occupancy.sh b/tools/bank_occupancy.sh
new file mode 100755
index 00000000..8638d390
--- /dev/null
+++ b/tools/bank_occupancy.sh
@@ -0,0 +1,31 @@
+#!/bin/bash
+MACHINE="$1"
+if [[ ! -s output-main/rtlplayground.map ]]; then
+    original_branch=$(git branch --show-current)
+    #trap 'git switch "$original_branch"' EXIT
+    git switch main && make CI=1 MACHINE="$MACHINE" BUILDDIR=output-main
+    git switch "$original_branch"
+fi
+source <(sed -rn 's/^([XCD]SEG|(BANK[0-9])).*=\s+([0-9]+)\. bytes.*$/main_\1=\3/p' output-main/rtlplayground.map | sort -u)
+
+main_WEB=$(du -sb output-main/html_min | awk '{print $1}')
+if [[ ! -s "output/$MACHINE/rtlplayground.map" ]]; then
+    make CI=1 MACHINE="$MACHINE"
+fi
+source <(sed -rn 's/^([XCD]SEG|(BANK[0-9])).*=\s+([0-9]+)\. bytes.*$/branch_\1=\3/p' output/"$MACHINE"/rtlplayground.map | sort -u)
+branch_WEB=$(du -sb output/html_min | awk '{print $1}')
+
+print_line() {
+  local name=$1 main=$2 branch=$3
+  printf '%-20s %-20s %-20s %-20s\n' "$name" "$main" "$branch" "$((branch - main))"
+}
+
+printf '%-20s %-20s %-20s %-20s\n' "segment" "main" "branch" "change"
+
+print_line "BANK1" "$main_BANK1" "$branch_BANK1"
+print_line "BANK2" "$main_BANK2" "$branch_BANK2"
+print_line "BANK3" "$main_BANK3" "$branch_BANK3"
+print_line "CSEG" "$main_CSEG" "$branch_CSEG"
+print_line "DSEG" "$main_DSEG" "$branch_DSEG"
+print_line "XSEG" "$main_XSEG" "$branch_XSEG"
+print_line "WEB" "$main_WEB" "$branch_WEB"