Baremetal ARM Proramming using qemu vexpress-a9 board

This is my attempt to do baremetal programming on cortex-a9 using qemu and vexpress-a9 board.

Working

Keyboard using ARM (PL050)
Display using ARM (PL111)
Timer usin ARM (SP804)
UART using ARM (PL011)
SD card using ARM (PL181)
Real Time Clock (RTC) using ARM (PL031)
Interrrupts using ARM (GIC) and IRQ code stub
µGUI - free and open source graphic library for embedded systems Port
FatFs - Generic FAT Filesystem Module Port
uClibc - C library for developing embedded Linux systems syscall Port

Plans for Future

Code Cleanup & Refactoring
Better Build Script and IDE Support (Debugging, Building, and Running)
Audio Support using ARM Advance Audio Codec Interface (PL041)
Network Support using LAN9118 ethernet
Porting Network Stack using lwIP
MultiCore Support
Better Driver Support and Imporovements
Code Documentation and overall Walkthrough
Detailed Walkthrough of My BareMetal Adventure

Dependencies

arm-none-eabi
qemu-system-arm
gdb-multiarch (only if you need to debug)

How to Run

I've tested this on Linux platform only, the Makefile is hopefully easy to read, you can change flags there

make will build the project
make qemu will run elf kernel in qemu
make dqemu will instruct qemu to pause execution and listen for gdb remote connection on port 1234
make gdb will run the gdb-multiarch [do this in seperate terminal and after runnin make dqemu]
- note you need to execute target remote :1234 to connect to qemu debug port

Quick Code Walkthrough

In this section I'll briefly highlight main point of important file. This will help explain the big picture. Hopefully, I'll write detailed guide in future.

Linker Script linker.ld:

ensures Interrupt vector is at the start of the kernel binary
contains necessary symbols for stack, heap, ulibc, ...etc to work (refrenced by startup.S) and _sbrk() for malloc()
describe how the final layout of the binary

Code entry point is the statup.S which will do the following:

Initialize the interrupt vectors
Initialize the stack and ARM code
jump to C code

ulibC and syscall.c:

contains implemenation of needed stubs for standard C library to work properly
_write has been implemented to print to uart. This will allow printf to work
_sbrk has been implemented utilizing symbols in linker.ld. This will allow malloc to work
before jumping to main standard C will initialize the .bss section to zero (C runtime)

interrupt.c and gic.c:

here we Initialize the ARM GIC (Generic Interrupt Controller)
c_irq is the function that will handle irq. The function works by getting the IRQ# (who triggered the interrupt) and then use this number to check in a function pointer array (is there a handler for this irq?). if yes then call that handler, else print no handler found
install_isr function will allow device driver code to hook intterupt handler for specific IRQ# [c_irq will call this hook]
enable_irq will enable specified IRQ# in GIC

[[To be Continued..]]