QEMU with Pi 4 support

Switch to using QEMU branch with rpi4 support https://github.com/mcribbs/qemu-patch-raspberry4z

Author: mcribbs

Makefile

@@ -7,9 +7,9 @@ LDFLAGS = -nostdlib -nostartfiles
 
 # Machine and emulator targets
 CPU = cortex-a53
-QEMU_COMMAND = qemu-system-aarch64
-QEMU_MACHINE = raspi3b
-QEMU_RAM = 1024
+QEMU_COMMAND = ~/Code/ThirdParty/qemu-patch-raspberry4/build/qemu-system-aarch64
+QEMU_MACHINE = raspi4b2g
+QEMU_RAM = 2048
 
 # Source directories (add additional subdirectories here)
 SRC_DIRS  = src/bootstrapper

README.md

@@ -5,7 +5,9 @@ An OS for Raspberry Pi
    - ~~brew: `gcc-arm-embedded`~~ This is 32 bit only, 64bit not available on brew
    - Extract this [pre-built cross-compiler toolchain](https://github.com/thinkski/osx-arm-linux-toolchains/releases/download/8.3.0/aarch64-unknown-linux-gnu.tar.xz) into the build folder (should be located at `$PROJECT/build/aarch64-unkown-linux-gnu`)
 2. [QEMU](https://www.qemu.org/download/)
-   - brew: `qemu`
+3. - ~~brew: `qemu`~~ Version on brew does not support the Raspberry Pi 4
+   - Checkout this [patched fork](https://github.com/mcribbs/qemu-patch-raspberry4) and compile.
+   - Update QEMU_COMMAND in the Makefile with the location of your built binary
 ## Resources
 - https://jsandler18.github.io/ - This is old and targets 32bit machines
 - https://github.com/s-matyukevich/raspberry-pi-os