ARM64 Target (Raspberry Pi 3 / QEMU)

The arm64 target compiles Yog programs to AArch64 machine code for Raspberry Pi 3 and QEMU.

Entry Point

ARM64 programs define a single main() function. The bootstrap sets up the stack pointer and calls it. If main() returns, the CPU halts.

function main(): void {
    uart_init();
    uart_print("Hello, World!\n");
}

Compile

yogc examples/arm64-hello/main.yog kernel8.img
# or explicitly:
yogc --target arm64 examples/arm64-hello/main.yog kernel8.img

arm64 is the default target, so --target is optional.

Run in QEMU

Install QEMU:

brew install qemu           # macOS
sudo apt install qemu-system-aarch64  # Ubuntu/Debian

Boot:

qemu-system-aarch64 -M raspi3b -kernel kernel8.img -serial stdio -display none

Expected output:

Hello, World!

Press Ctrl-A X to quit QEMU.

Run on Real Hardware (Raspberry Pi 3)

1. Format an SD card as FAT32.

2. Download the Raspberry Pi firmware: bootcode.bin, start.elf, fixup.dat.

3. Copy those files plus your kernel8.img to the SD card root.

4. Create config.txt with:

   enable_uart=1
   arm_64bit=1

5. Insert the SD card, connect a USB-serial adapter to GPIO pins 14/15, and power on.

6. Open a terminal at 115200 baud to see output.

Hardware Details

Property	Value
CPU	ARM Cortex-A53 (AArch64)
Load address	0x80000
UART	PL011 at 0x3F201000
Baud rate	115200 (48 MHz ref clock)

Boot Sequence

The VideoCore GPU reads kernel8.img from the SD card and loads it at 0x80000. Execution starts at the very first instruction (the bootstrap stub). The stub:

1. Reads MPIDR_EL1 to get the core ID.
2. Parks cores 1–3 in a WFE loop.
3. Sets SP = 0x80000 (stack grows down from the load address).
4. Calls main().
5. Hangs if main() returns.

Intrinsics Available

Call	Description
uart_init()	Initialise PL011 UART at 115200 baud
uart_print("...")	Write a string literal to UART
Memory.read32(addr)	Load a 32-bit MMIO register
Memory.write32(addr, val)	Store a 32-bit MMIO register