Add the baremetal target to the readme

README.md

@@ -12,12 +12,12 @@ The main goal of this project is to be able to play Pokemon on my own emulator.
 
 **More will be added if neccessary (and by neccessary I mean if games I want to play will require them)**
 
-## How to use
+## Building
 
-### Building
+### Desktop
 
 ```shell
-cargo build --release --features [optional_features]
+cargo build --release --package gb --features [optional_features]
 ```
 #### Optional features:
 * `sdl` - Link to sdl2 (On by default)
@@ -32,7 +32,7 @@ On by default
 
 > **Note** to turn off on by default features pass `--no-default-features` when building
 
-### Key bindings:
+#### Key bindings:
 
 | Joypad     | Keyboard    |
 | ---------- | ----------- |
@@ -45,17 +45,38 @@ On by default
 | Dpad Left  | Left arrow  |
 | Dpad Right | Right arrow |
 
-### Running
+### Raspberry Pi Baremetal (with ili9341 display and gpio buttons)
 
-#### Desktop
+1. Install the rust nightly toolchain for `armv7a-none-eabihf`:
+```shell
+rustup target add armv7a-none-eabihf --toolchain nightly
+rustup +nightly component add rust-src
+```
+
+Unfurtuantly `armv7a-none-eabihf` is a [tier3](https://doc.rust-lang.org/nightly/rustc/platform-support.html#tier-3) target for the Rust compiler so building for it requires the nightly toolchain - [source](https://stackoverflow.com/questions/67352828/how-to-build-for-tier-3-target-not-included-in-rustup-target-list)
+
+> **Notice** Verify that you install the `armv7a-none-eabihf` target and not the `armv7a-none-eabi` target, as the later doesn't have support for hardware floats.
+
+2. Install Cargo Binutils:
+```shell
+cargo install cargo-binutils
+rustup component add llvm-tools-preview
+```
+
+3. Edit the relevant settings in `configuration.rs`
+4. Run `build.sh` or `build.bat` which will compile and create an bootable image called `kernel7.img`
+
+## Running
+
+### Desktop
 ```sh
 magenboy [path_to_rom] [other_optional_flags]
 ```
 
-#### Raspberry Pi
+### Raspberry Pi Desktop with peripherals
 See - [RealMagenBoy](docs/RealMagenBoy.md)
 
-### Optional flags
+#### Optional flags
 
 * `--file-audio` - Saves the audio to a file
 * `--full-screen` - Full screen mode
@@ -66,6 +87,37 @@ Choose a game with the Joypad bindings (Dpad and A to confirm)
 * `--mode [mahcine mode]` - Override the auto machine detection for the game (mode can be: `CGB` - Gameboy color | `DMG` - Original Gameboy  | `ANY` - default)
 * `--shutdown-rpi` - Requires `rpi` feature, shutdown the RPi upon shutdown of the program
 
+### Raspberry Pi Baremetal
+
+Currently only Raspberry Pi 4 is supported using the following instructions:
+* Format a sd card and make a single `FAT32` partition called `boot`
+* Copy the file `config.txt` to the root dir of the sd card
+* Copy the following files from the [Raspberry Pi firmware repo](https://github.com/raspberrypi/firmware/tree/master/boot) onto the SD card:
+    - [fixup4.dat](https://github.com/raspberrypi/firmware/raw/master/boot/fixup4.dat)
+    - [start4.elf](https://github.com/raspberrypi/firmware/raw/master/boot/start4.elf)
+    - [bcm2711-rpi-4-b.dtb](https://github.com/raspberrypi/firmware/raw/master/boot/bcm2711-rpi-4-b.dtb)
+* Copy `kernel7.img` onto the SD card
+* Connect all the peripherals (ili9341 display and gpio buttons)
+* Insert the SD card to the RPI4 and boot it
+
+_**Note**: Should it not work on your RPi4, try renaming `start4.elf` to `start.elf` (without the 4)
+on the SD card._
+
+### QEMU
+
+Currently Qemu doesn't support RPI4 in 32 bit mode, so in order to test it I added support for RPI2 mapping.
+To change to RPI2 mode build with the `rpi2` feature and not the default `rpi4` feature.
+
+running with qemu:
+```shell
+qemu-system-arm.exe -M raspi2b -serial null -serial mon:stdio -kernel path_to_elf
+```
+
+_**Note** Qemu takes the path to the elf generated by cargo not the image generated by binutils_
+the UART output will be written to the console.
+
+I think that not all the peripherals I use are implemented in QEMU so I used this mainly to debug boot and CPU initialization problems
+
 ## GameBoy
 
 ### Development Status
@@ -125,4 +177,15 @@ Choose a game with the Joypad bindings (Dpad and A to confirm)
 - [Raspberry Pi docs](https://www.raspberrypi.com/documentation/computers/processors.html)
 - [juj/fbcp-ili9341 as a refference](https://github.com/juj/fbcp-ili9341)
 - [Raspberry Pi DMA programming in C](https://iosoft.blog/2020/05/25/raspberry-pi-dma-programming/)
-- [Ili9341 docs](https://cdn-shop.adafruit.com/datasheets/ILI9341.pdf)
+- [Ili9341 docs](https://cdn-shop.adafruit.com/datasheets/ILI9341.pdf)
+#### BareMetal RaspberryPi
+- [Bare-metal Boot Code for ARMv8-A](http://classweb.ece.umd.edu/enee447.S2021/baremetal_boot_code_for_ARMv8_A_processors.pdf)
+- [Low performance Baremetal code Blog post](https://forums.raspberrypi.com/viewtopic.php?t=219212)
+- [Raspberry-Pi-Multicode examples by LdB-ECM](https://github.com/LdB-ECM/Raspberry-Pi)
+- [RaspberryPi official Linux fork](https://github.com/raspberrypi/linux)
+- ARM official Docs
+    - [ARM Cortex-A72 manual](https://developer.arm.com/documentation/100095/0003)
+    - [ARMv7-A Architecture Reference Manual](https://developer.arm.com/documentation/ddi0406/cb/?lang=en)
+    - [ARMv8-A Architecture Reference Manual](https://developer.arm.com/documentation/ddi0487/ia/?lang=en)
+    - [ARMv8-A Registers](https://developer.arm.com/documentation/ddi0595/2021-12/AArch32-Registers/CCSIDR--Current-Cache-Size-ID-Register?lang=en)
+    - [ARMv7-A programmer Guide](https://developer.arm.com/documentation/den0013/latest/)