Minimal ARM Operating System for the Raspberry Pi 4, supporting aarch64 architectures.

Lines of code:

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Language                     files          blank        comment           code
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C                               14            191            263            765
C/C++ Header                    24            152            353            326
Assembly                         6             61            163            208
Markdown                         1              4              0             61
make                             1             19             12             54
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SUM:                            46            427            791           1414
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Support for:

• Raspberry Pi 4

• Basic Directory Structure
• Register Addresses
  • GPIO
  • AUX
• mini UART
• Kernel printing info on start up
• printk
• string.h functions
  • strlen, strcmp, strcpy, strcat, strrev
  • memset, memcpy
• stdlib.h functions
  • itoa
  • atoi
• stdbool
  • true, false
• Exception Levels (ARMv8-a)
  • armstub starts kernel at EL3
  • Kernel starts at EL3
  • Print EL
  • Change from EL3 to EL1
• Interrupts - IRQ
  • Initialize vector table
  • Enable / Disable interrupts
  • IRQ registers
  • Handle mini UART interrupts
  • Handle Timer interrupts
• Timer
  • System Timer 1 init (set interval from param)
  • System Timer 1 handler
  • System Timer 1 stop
  • Sleep (msec)
• GPIO
  • Functions for set/clear pins
  • Function for seting Alt Func to GPIO pins
• Console
  • prompt
  • Take users input
  • Command parser
  • Handle Commands
  • Commands
    • help
    • halt
    • create_procs
    • run_procs
• Processes
  • Scheduler
  • Context Switch
  • Fork
  • Process initialization
  • Parameterize processes:
    • Number
    • Argument
    • Kill process

A screenshots where, we create 4 processes, run them and kill them: