GameSphere

A Raspberry Pi game console kernel with a fixed function render pipeline. The purpose of the GameSphere project is to provide a modern, well-documented, and maintained system for low-level graphics programming enthusiasts and those nostalgic for 6th gen gaming consoles.

CPU Models

Raspberry Pi 3/3b

cortex-a53

Raspberry Pi 4+

cortex-a72

Commands

Compiling for cortex-a53 (Raspberry Pi 3b)

make raspi3

Compiling for cortex-a72 (Raspberry Pi 4+)

make raspi4

Note: Defaults to cortex-a53 for QEMU debugging if none is specified.

QEMU & Debugging

This command will disable the QEMU monitor and redirect the UART0 output to the terminal

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

Running QEMU with logging

qemu-system-aarch64 -M raspi3b -kernel kernel8.img -serial stdio -monitor none -nographic -d cpu_reset,int -D qemu-log.txt

QEMU with GDB Debugging Support

Launching QEMU with GDB support

qemu-system-aarch64 -M raspi3b -kernel kernel8.img -serial stdio -monitor none -nographic -S -s

Attach GDB to QEMU (Note: Use the kernel8.elf for debugging not the kernel8.img)

gdb-multiarch kernel8.elf

target remote localhost:1234

Set breakpoints

b configure_mmio_base
continue

Step through

next    # Step to the next line
print debug_reg    # Print the value of the debug_reg pointer
print *debug_reg   # Print the value stored in the debug register

Inspect memory

x/x 0x3F003000  # Examine the memory at the debug register address (Pi 3B)

Device Tree Souce (dt-blob.dts)

Compile command

dtc -I dts -O dtb -o dt-blob.bin dt-blob.dts

Misc.

GDB Commands

Set variable

set $pc=0x80000

Inspect registers

info registers

Examine PC

x/4i $pc  # Disassemble 4 instructions at the current PC

Start execution

continue

Disassemble binary

aarch64-none-elf-objdump -D -b binary -m aarch64 kernel8.img

Misc. Commands

Examine ELF and Binary Contents

readelf -h bin/kernel8.elf | grep "Entry point"

CMD - Copy Binaries to SD Card

Copy-Item -Path .\config.txt -Destination D:\
Copy-Item -Path .\dt-blob.bin -Destination D:\
Copy-Item -Path .\fixup4.dat -Destination D:\
Copy-Item -Path .\kernel8.img -Destination D:\
Copy-Item -Path .\start4.elf -Destination D:\