https://github.com/marwan475/twistedos

32 bit OS with a rtl8139 network card driver
https://github.com/marwan475/twistedos

2stagebootloader bootloader driver interrupt-handler memory-management network osdev rtl8139 usermode virtualmemory

Last synced: 16 days ago
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32 bit OS with a rtl8139 network card driver

• Host: GitHub
• URL: https://github.com/marwan475/twistedos
• Owner: marwan475
• Created: 2024-10-26T02:15:50.000Z (4 months ago)
• Default Branch: main
• Last Pushed: 2025-01-21T06:55:55.000Z (23 days ago)
• Last Synced: 2025-01-21T07:29:15.106Z (23 days ago)
• Topics: 2stagebootloader, bootloader, driver, interrupt-handler, memory-management, network, osdev, rtl8139, usermode, virtualmemory
• Language: C
• Homepage:
• Size: 118 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# TwistedOS

x86 32 bit OS from scratch

## Design

#### 2 stage boot loader

- stage 1 loads the FAT 12 table then loads in stage 2 of the bootloader

- stage 2 loads the entire kernel from the FAT 12 file system at above 1mb of memory

  - Initializes GDT

  - Switches to 32 bit mode

  - Jumps execution to kernel code

- 2 stages are used due to the 512 byte limit of the inital bootloader and the 1mb limit on 20bit addressing (16 bit + A gate)

#### Kernel

- installs TSS to allow for interupt handling in user mode

- Set up IDT for interrupt handling

- Initalizes IDT with ISRs

- remaps the PIC to allow for interrupts

- Sets up keyboard driver

- enables interrupts

- Initalizes physical memory manager

  - bit map that manges the workable memory range using blocks of 4096 (size of pages)

- Initalizes virtual memory

  - sets up page table dir and page tables

  - identiy maps first 16mb of memory

  - allocates space for pages using physical memory manager

- Initializes network card driver for rtl8139

  - card sends interrupt any time a packet is recv or sent

- ethernet layer

  - checks if packet is an ARP request or IPv4

- Console support

  - console printing support for output and debugging

  - user is able to enter commands

  - user can enumerate PCI devices

  - user can clear screen

## Resources

https://www.ctyme.com/intr/rb-0106.htm 

https://www.ctyme.com/intr/rb-0607.htm // interrupt codes

https://www.eit.lth.se/fileadmin/eit/courses/eitn50/Literature/fat12_description.pdf // FAT12

https://wiki.osdev.org/Rolling_Your_Own_Bootloader

https://wiki.osdev.org/Creating_an_Operating_System

https://www.sqlpassion.at/archive/2022/03/03/reading-files-from-a-fat12-partition/

https://www.calculator.net/hex-calculator.html?number1=7E00&c2op=%2B&number2=2800&calctype=op&x=Calculate

https://wiki.osdev.org/Memory_Map_(x86)

http://www.brokenthorn.com/Resources/OSDev18.html

https://www.rapidtables.com/convert/number/hex-to-binary.html?x=D

https://wiki.osdev.org/PCI

https://wiki.osdev.org/RTL8139

http://realtek.info/pdf/rtl8139cp.pdf

https://ics.uci.edu/~harris/ics216/pci/PCI_22.pdf

https://github.com/dreamportdev/Osdev-Notes/tree/master/06_Userspace

https://en.wikipedia.org/wiki/Ethernet_frame

https://en.wikipedia.org/wiki/Address_Resolution_Protocol