diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
new file mode 100644
index 0000000..f82a79a
--- /dev/null
+++ b/.github/workflows/build.yml
@@ -0,0 +1,38 @@
+name: build
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  build:
+    name: ${{ matrix.os }} / SDL ${{ matrix.sdl }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+        sdl: [1, 2]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install SDL (Ubuntu)
+        if: runner.os == 'Linux'
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y libsdl1.2-dev libsdl2-dev
+
+      - name: Install SDL (macOS)
+        if: runner.os == 'macOS'
+        run: brew install sdl12-compat sdl2
+
+      - name: Build
+        run: make SDL=${{ matrix.sdl }}
+
+      - name: Build z80emu CPU core
+        run: make clean && make CPU=z80emu SDL=${{ matrix.sdl }}
+
+      - name: CPU tests
+        run: make test
diff --git a/.gitignore b/.gitignore
index c12294e..33ca572 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,9 @@
 obj
+objhtml
 zxem
-maketables
\ No newline at end of file
+zxem.html
+zxem.js
+zxem.data
+maketables
+tests/zxtest
+tests/zxtest.log
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index ce2a5b0..0000000
--- a/.travis.yml
+++ /dev/null
@@ -1,7 +0,0 @@
-language: c
-
-before_script:
-    - sudo apt-get update -qq
-    - sudo apt-get install libsdl1.2-dev
-
-script: make
diff --git a/INSTALL b/INSTALL
index 0272a8f..92d9531 100644
--- a/INSTALL
+++ b/INSTALL
@@ -1,4 +1,5 @@
-For Linux or Mac, just type "make". It will compile the example zextest. 
+For Linux or Mac, install SDL 1.2 or SDL2 and type "make" to build zxem.
+See README.md for the build options (SDL=2, DEBUG=1, PLAT=HTML, make test).
 
 For Windows, open a Visual C++ command prompt and then type:
 
diff --git a/Makefile b/Makefile
index a271e55..5038d26 100644
--- a/Makefile
+++ b/Makefile
@@ -1,136 +1,132 @@
 # ZXEM MAKEFILE
-OLEVEL = -O3 
-CFLAGS =  -Isrc/zxem -Isrc/osdep -Isrc/cpu -Wall -pedantic $(OLEVEL) -fomit-frame-pointer
-SDL = 1
-ZCC = $(ZCC)
-#CPU = z80emu
-#CPU = mz80
-#CPU = deadz80
-CPU = z80core
+#
+# make               native build (SDL 1.2, z80core CPU)
+# make SDL=2         build against SDL2
+# make SDL=0         build with the dummy (no video) backend
+# make DEBUG=1       debug build (-O0 -g)
+# make PLAT=HTML     Emscripten build (zxem.html)
+# make test          build and run the CPU test suite (z80emu core)
+
+## Config
+
+# CPU core: z80core (default), z80emu, mz80 (mz80 has issues on 64-bit)
+CPU ?= z80core
+SDL ?= 1
+PLAT ?= NATIVE
 
 TARGET = zxem
 TEST_TARGET = tests/zxtest
-OBJDIR = obj
-ifndef PLAT
-PLAT = NATIVE
-endif
+
+CPPFLAGS += -Isrc/zxem -Isrc/osdep -Isrc/cpu
+WARNINGS = -Wall -pedantic
+CFLAGS += $(WARNINGS) -fomit-frame-pointer
+CXXFLAGS += $(WARNINGS) -std=c++11 -fomit-frame-pointer
 
 ifdef DEBUG
 OLEVEL = -O0 -g
+else
+OLEVEL = -O2
 endif
+CFLAGS += $(OLEVEL)
+CXXFLAGS += $(OLEVEL)
 
-OSD_SOURCE = src/osdep/dummy.c
-
-ifdef SDL
-ifeq ($(SDL), 1)
-OSD_SOURCE = src/osdep/sdl1.2.c
-OSDFLAGS = $(shell sdl-config --cflags)
-OSDLIBS = $(shell sdl-config --libs)
-endif
-ifeq ($(SDL), 2)
-OSD_SOURCE = src/osdep/sdl2.c
-OSDFLAGS = $(shell sdl2-config --cflags)
-OSDLIBS = $(shell sdl2-config --libs)
-endif
-endif
-
+## Platform specific config
 
 ifeq ($(PLAT), HTML)
-ZCC = emcc
+CC = emcc
+CXX = em++
 AR = emar
-OSDFLAGS = -s USE_SDL=$(SDL)
-OSDLIBS = 
-OLEVEL += -s ASM_JS=1 
-LINKFLAGS = $(OSDFLAGS) $(OLEVEL) --preload-files roms/ --preload-files scr/ --emrun
-TARGET := $(TARGET).html
 OBJDIR = objhtml
+SDLFLAGS = -s USE_SDL=$(SDL)
+OSDLIBS =
+LINKFLAGS += $(SDLFLAGS) --preload-file roms --preload-file scr --emrun
+TARGET := $(TARGET).html
+else
+OBJDIR = obj
 endif
 
-ifeq ($(CPU), z80emu)
-CPUOBJ = $(OBJDIR)/z80emu.o
-CPUINTC = src/cpu/z80emu/cpuintf.c
-endif
+## OS dependent (video/input) backend
 
-ifeq ($(CPU), mz80)
-CPUOBJ = $(OBJDIR)/mz80.o
-CPUINTC = src/cpu/mz80/cpuintf.c
+ifeq ($(SDL), 1)
+OSD_SOURCE = src/osdep/sdl1.2.c
+ifneq ($(PLAT), HTML)
+SDLFLAGS = $(shell sdl-config --cflags)
+OSDLIBS = $(shell sdl-config --libs)
 endif
-
-ifeq ($(CPU), deadz80)
-CPUOBJ = $(OBJDIR)/deadz80.o
-CPUINTC = src/cpu/deadz80/cpuintf.c
+else ifeq ($(SDL), 2)
+OSD_SOURCE = src/osdep/sdl2.c
+ifneq ($(PLAT), HTML)
+SDLFLAGS = $(shell sdl2-config --cflags)
+OSDLIBS = $(shell sdl2-config --libs)
 endif
-
-ifeq ($(CPU), z80core)
-CPUOBJ = $(OBJDIR)/z80core_Z80Core.o $(OBJDIR)/z80core_Z80Core_CBOpcodes.o $(OBJDIR)/z80core_Z80Core_DDCB_FDCBOpcodes.o $(OBJDIR)/z80core_Z80Core_DDOpcodes.o $(OBJDIR)/z80core_Z80Core_EDOpcodes.o $(OBJDIR)/z80core_Z80Core_FDOpcodes.o $(OBJDIR)/z80core_Z80Core_MainOpcodes.o $(OBJDIR)/z80core_Z80Core_CInterface.o
-CPUINTC = src/cpu/z80core/cpuintf.c
-
-# add permissive for initialising members in class definitions (Z80Core.h) 
-CFLAGS += -fpermissive
-
-#compile as c++ when using z80 core
-ifeq ($(PLAT), HTML) 
-ZCC = em++
 else
-ZCC = $(CXX)
-endif
-
+OSD_SOURCE = src/osdep/dummy.c
 endif
 
+## Sources: every .c/.cpp in the selected CPU directory plus src/zxem.
+## Helper programs (maketables, zextest) live in src/cpu/z80emu/util so
+## they are not picked up here.
 
-all: $(OBJDIR) $(TARGET) 
+CPUSRC  := $(wildcard src/cpu/$(CPU)/*.c) $(wildcard src/cpu/$(CPU)/*.cpp)
+ZXEMSRC := $(wildcard src/zxem/*.c)
 
-$(OBJDIR):
-	mkdir $(OBJDIR)
+obj_of = $(addprefix $(OBJDIR)/,$(addsuffix .o,$(subst /,_,$(patsubst src/%,%,$(basename $(1))))))
 
-tables.h: maketables.c
-	$(ZCC) -Wall $< -o maketables
-	./maketables > $@
+CPUOBJ  := $(call obj_of,$(CPUSRC))
+ZXEMOBJ := $(call obj_of,$(ZXEMSRC))
+OSDOBJ  := $(OBJDIR)/osdep.o
+OBJECTS := $(ZXEMOBJ) $(CPUOBJ) $(OSDOBJ)
 
-# MULTI CPU CORE!
-# Z80EMU - BROKEN
-$(OBJDIR)/z80emu.o: src/cpu/z80emu/z80emu.c src/cpu/z80emu/z80emu.h src/cpu/z80emu/instructions.h src/cpu/z80emu/macros.h src/cpu/z80emu/tables.h
-	$(ZCC) $(CFLAGS) -c $< -o $@
+HEADERS := $(wildcard src/*/*.h src/cpu/*/*.h)
 
-# MZ80 - Issues on 64bit :(
-$(OBJDIR)/mz80.o: src/cpu/mz80/mz80.c src/cpu/mz80/mz80.h src/cpu/cpuintf.h
-	$(ZCC) $(CFLAGS) -c $< -o $@
+## Rules
 
-# DEADZ80 - Dead?
-$(OBJDIR)/deadz80.o: src/cpu/deadz80/deadz80.c src/cpu/deadz80/deadz80.h src/cpu/deadz80/opcodes.h src/cpu/cpuintf.h
-	$(ZCC) $(CFLAGS) -c $< -o $@
+all: $(TARGET)
 
-# Z80CORE - SUCCESS!
-$(OBJDIR)/z80core_%.o: src/cpu/z80core/%.cpp
-	$(ZCC) $(CFLAGS) -c $< -o $@
+$(OBJDIR):
+	mkdir -p $(OBJDIR)
 
-#$(OBJDIR)/z80core.a: src/cpu/z80core/Z80Core.o src/cpu/z80core/Z80Core_CBOpcodes.o src/cpu/z80core/Z80Core_DDCB_FDCBOpcodes.o src/cpu/z80core/Z80Core_DDOpcodes.o src/cpu/z80core/Z80Core_EDOpcodes.o src/cpu/z80core/Z80Core_FDOpcodes.o src/cpu/z80core/Z80Core_MainOpcodes.o
-#	$(AR) cr $@ src/cpu/z80core/*.o
+define compile_c
+$(call obj_of,$(1)): $(1) $(HEADERS) | $(OBJDIR)
+	$$(CC) $$(CPPFLAGS) $$(CFLAGS) -c $$< -o $$@
+endef
+define compile_cxx
+$(call obj_of,$(1)): $(1) $(HEADERS) | $(OBJDIR)
+	$$(CXX) $$(CPPFLAGS) $$(CXXFLAGS) -c $$< -o $$@
+endef
 
-$(OBJDIR)/zxem.o: src/zxem/zxem.c src/zxem/zxem.h src/osdep/osdep.h
-	$(ZCC) $(CFLAGS) $(OSDFLAGS) -c $< -o $@
+$(foreach src,$(filter %.c,$(CPUSRC)) $(ZXEMSRC),$(eval $(call compile_c,$(src))))
+$(foreach src,$(filter %.cpp,$(CPUSRC)),$(eval $(call compile_cxx,$(src))))
 
-$(OBJDIR)/zxvid.o: src/zxem/zxvid.c src/zxem/zxem.h src/osdep/osdep.h
-	$(ZCC) $(CFLAGS) -c $< -o $@
+$(OSDOBJ): $(OSD_SOURCE) $(HEADERS) | $(OBJDIR)
+	$(CC) $(CPPFLAGS) $(CFLAGS) $(SDLFLAGS) -c $< -o $@
 
-$(OBJDIR)/zxio.o: src/zxem/zxio.c src/zxem/zxem.h src/osdep/osdep.h
-	$(ZCC) $(CFLAGS) -c $< -o $@
+# Link with the C++ driver so the C++ runtime is pulled in for z80core.
+$(TARGET): $(OBJECTS)
+	$(CXX) $(CXXFLAGS) $(OBJECTS) $(OSDLIBS) $(LINKFLAGS) -o $@
 
-$(OBJDIR)/osdep.o: $(OSD_SOURCE) src/zxem/zxem.h src/osdep/osdep.h
-	$(ZCC) $(CFLAGS) $(OSDFLAGS) -c $(OSD_SOURCE) -o $@
+## CPU test suite (exercises the z80emu core, whichever CPU zxem uses)
 
-$(OBJDIR)/cpuintf.o: $(CPUINTC) 
-	$(ZCC) $(CFLAGS) -c $< -o $@
+$(OBJDIR)/test_z80emu.o: src/cpu/z80emu/z80emu.c $(wildcard src/cpu/z80emu/*.h) | $(OBJDIR)
+	$(CC) $(CPPFLAGS) $(CFLAGS) -c $< -o $@
 
-OBJECT_FILES = $(OBJDIR)/zxem.o $(CPUOBJ) $(OBJDIR)/zxvid.o $(OBJDIR)/zxio.o $(OBJDIR)/osdep.o $(OBJDIR)/cpuintf.o
+$(TEST_TARGET): tests/cputest.c src/cpu/z80emu/z80emu.h $(OBJDIR)/test_z80emu.o
+	$(CC) $(CPPFLAGS) $(CFLAGS) $< $(OBJDIR)/test_z80emu.o -o $@
 
-$(TARGET): $(OBJECT_FILES)
-	$(ZCC) $(CFLAGS) $(OBJECT_FILES) $(OSDLIBS) $(LINKFLAGS) -o $@
+# The suite stops at the first failure. The z80emu core currently passes the
+# first $(KNOWN_PASSES) tests and fails at cb46 (BIT 0,(HL): undocumented
+# flag bits 3/5 come from MEMPTR, which z80emu does not model). Fail the
+# build if that number goes down, so new regressions are caught.
+KNOWN_PASSES ?= 286
 
-$(TEST_TARGET): tests/cputest.c src/cpu/z80emu/z80emu.h $(OBJDIR)/z80emu.o
-	$(ZCC) $(CFLAGS) $< $(OBJDIR)/z80emu.o  -o $@
+test: $(TEST_TARGET)
+	@(cd tests && ./zxtest > zxtest.log); \
+	  passed=$$(grep -c PASSED tests/zxtest.log); \
+	  echo "cputest: $$passed tests passed (expected at least $(KNOWN_PASSES))"; \
+	  grep -B1 -A15 FAILED tests/zxtest.log | grep -v '^[ 0-9]*M[RW] ' ; \
+	  test $$passed -ge $(KNOWN_PASSES)
 
+clean:
+	rm -rf obj objhtml $(TARGET) zxem.html zxem.js zxem.data $(TEST_TARGET) tests/zxtest.log
 
-clean: 
-	rm $(OBJDIR)/*.o 
-	rm $(TARGET)
+.PHONY: all clean test
diff --git a/README.md b/README.md
index 8271376..505e3f3 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,26 @@ ZXEMU is a free open source cross platform ZX Spectrum emulator, currently work
 
 [Play online](http://js.mikedx.co.uk/zxem.html)
 
-[![Build Status](https://travis-ci.org/MikeDX/z80emu.svg?branch=master)](https://travis-ci.org/MikeDX/z80emu)
+[![build](https://github.com/MikeDX/z80emu/actions/workflows/build.yml/badge.svg)](https://github.com/MikeDX/z80emu/actions/workflows/build.yml)
+
+## Building
+
+Install SDL 1.2 (or SDL2) first:
+
+- Ubuntu/Debian: `sudo apt-get install libsdl1.2-dev libsdl2-dev`
+- macOS (Homebrew): `brew install sdl12-compat sdl2`
+
+Then:
+
+```
+make            # zxem with SDL 1.2
+make SDL=2      # zxem with SDL2
+make DEBUG=1    # debug build
+make PLAT=HTML  # Emscripten build (zxem.html)
+make test       # build and run the CPU test suite
+```
+
+Run `./zxem` from the repository root (it loads `roms/48k.rom`).
 
 ## TODO list
 - [x] Working Z80 CPU Core  
diff --git a/src/cpu/z80core/Z80Core.h b/src/cpu/z80core/Z80Core.h
index ac64ca3..7226f3e 100644
--- a/src/cpu/z80core/Z80Core.h
+++ b/src/cpu/z80core/Z80Core.h
@@ -146,7 +146,7 @@ class CZ80Core
 	typedef struct
 	{
 		void (CZ80Core::*function)(unsigned char opcode);
-		char* format;
+		const char* format;
 	} Z80Opcode;
 
 	typedef struct
diff --git a/src/cpu/z80core/Z80Core_CInterface.h b/src/cpu/z80core/Z80Core_CInterface.h
index ead9be5..264b446 100644
--- a/src/cpu/z80core/Z80Core_CInterface.h
+++ b/src/cpu/z80core/Z80Core_CInterface.h
@@ -64,7 +64,7 @@ typedef enum
 
 //-----------------------------------------------------------------------------------------
 
-void *Z80CORE_Create();
+void *Z80CORE_Create(void);
 void Z80CORE_Destroy(void *core);
 void Z80CORE_Initialise(void *core, Z80CoreRead mem_read, Z80CoreWrite mem_write, Z80CoreRead io_read, Z80CoreWrite io_write, Z80CoreContention mem_contention_handling, Z80CoreContention io_contention_handling, int member_class);
 void Z80CORE_Reset(void *core);
diff --git a/src/cpu/z80emu/maketables.c b/src/cpu/z80emu/util/maketables.c
similarity index 100%
rename from src/cpu/z80emu/maketables.c
rename to src/cpu/z80emu/util/maketables.c
diff --git a/src/cpu/z80emu/zextest.c b/src/cpu/z80emu/util/zextest.c
similarity index 100%
rename from src/cpu/z80emu/zextest.c
rename to src/cpu/z80emu/util/zextest.c
diff --git a/src/cpu/z80emu/zextest.h b/src/cpu/z80emu/util/zextest.h
similarity index 100%
rename from src/cpu/z80emu/zextest.h
rename to src/cpu/z80emu/util/zextest.h
diff --git a/src/cpu/z80emu/z80emu.h b/src/cpu/z80emu/z80emu.h
index fe73e7c..9e9eb56 100644
--- a/src/cpu/z80emu/z80emu.h
+++ b/src/cpu/z80emu/z80emu.h
@@ -248,13 +248,6 @@ typedef struct Z80_STATE_ {
  *                      register_table for 0xdd or 0xfd prefixes.
  */
 
-/* Here are macros for the zextest example. Read/write memory macros have been 
- * written for a linear 64k RAM. Input/output port macros are used to simulate 
- * system calls.
- */
-
-#include "zextest.h"
-
 #define Z80_FETCH_BYTE(address, x)                                      \
 {                                                                       \
         (x) = state->readbyte(address); \
diff --git a/src/osdep/sdl2.c b/src/osdep/sdl2.c
index 680354d..f31de5e 100644
--- a/src/osdep/sdl2.c
+++ b/src/osdep/sdl2.c
@@ -7,7 +7,7 @@
  * 
  * OSDEP file for SDL2
  */
-#include <SDL2/SDL.h>
+#include <SDL.h>
 #include "osdep.h"
 #include "zxem.h"
 
diff --git a/tests/cputest.c b/tests/cputest.c
index 0683bab..03acc9b 100644
--- a/tests/cputest.c
+++ b/tests/cputest.c
@@ -13,6 +13,7 @@ uint8_t writes[65536];
 uint8_t reads[65536];
 
 int total, running, debug;
+int failed = 0;
 
 uint8_t readbyte(uint16_t addr) {
 //	printf("Reading 0x%X\n",addr);
@@ -273,6 +274,7 @@ int main(int argc, char *argv[]) {
 
 			printf("TSTATES: %d : %d\n", etstates, tstates);
 
+			failed = 1;
 			break;
 		}
 	}
@@ -281,6 +283,6 @@ int main(int argc, char *argv[]) {
 	printf("DONE\n");
 
 	free(zxmem);
-	return 0;
+	return failed;
 
 }