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# Jobbed
## Notice
- Currently `make -f Unix.mk copy` has a default disk /dev/sdc1. If you run it, it will mount this, copy the built image, and then unmount it.
- While this wouldn't overwrite any data, the unmounting of this disk may be errant on your computer configuration, causing you to lose access to files until you remount the disk.
- This will be changed in a few releases, but as it stands currently, this warning is here to prevent any transient problems
## Building (Debian)
- Clone the repository.
- Ensure you have the `arm-none-eabi-gcc` cross compiler installed.
- From the root of the directory, i.e. in `Jobbed`, execute `make -f Unix.mk`
## Building (Google Colab)
- `!git clone https://github.com/TerminalCursor/Jobbed.git`
- `!apt install gcc-arm-none-eabi`
- `!cd Jobbed; make -f Unix.mk`
- The built image is found in `Jobbed/build/kernel7.img` and can be copied to the root of the Raspberry Pi SD card's first parition
## Getting Cross Compiler
- https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/downloads
## Todo
- Finish Build Instructions
- Deterministic Graphics
- Move UART Polling Write to another method
- Make UART Write run as an event-based system
## Future
- USB Driver
- Ethernet Driver
- SPI Driver
- GPIO Falling Edge IRQ
## SVC Calls (In order)
- 0: Yield to threads in same priority
- 1: System Clock Time
- 2: Schedule
- 3: Add thread
- 4: Mutex Lock
- 5: Mutex Unlock
- 6: Semaphore Decrease
- 7: Semaphore Increase
- 8: Semaphore Increase by N
- 9: Cycle Counter
- A: Enable ARM Timer
- B: Disable ARM Timer
Note: SYS and USER share registers but differ in privilege
# Modes
- From https://developer.arm.com/documentation/den0013/d/ARM-Processor-Modes-and-Registers
- User: 10:10000 PL0
- FIQ : 11:10001 PL1
- IRQ : 12:10010 PL1
- SVC : 13:10011 PL1
- ABT : 17:10111 PL1
- HVC : 1A:11010 PL1
- UND : 1B:11011 PL1
- SYS : 1F:11111 PL1
# Registers
- From https://developer.arm.com/documentation/ddi0406/c/System-Level-Architecture/The-System-Level-Programmers--Model/ARM-processor-modes-and-ARM-core-registers/ARM-core-registers?lang=en
- User: r0-12_usr,sp_usr,lr_usr,CPSR
- FIQ: r8-r12_fiq,sp_fiq,lr_fiq,SPSR_fiq
- IRQ: sp_irq,lr_irq,SPSR_irq
- SVC: sp_svc,lr_svc,SPSR_svc
- ABT: sp_abt,lr_abt,SPSR_abt
- UND: sp_und,lr_und,SPSR_und
- SYS: Same as user
# Memory Layout
- 0x00004000 - 0x00008000 MMU Entries
- 0x00008000 - 0x0000F000 Code
- 0x0000F000 - 0x00010000 Data
- 0x00010000 - 0x000A3000 BSS
- 0x18000000 - 0x20000000 Thread Stacks
- 0x3F000000 - 0x40000000 MMIO
- 0x40000000 - 0xFFFFFFFF Local Peripherals
## Supplemental Links
- https://www.raspberrypi.com/documentation/computers/processors.html
- https://datasheets.raspberrypi.com/bcm2835/bcm2835-peripherals.pdf
- https://datasheets.raspberrypi.com/bcm2836/bcm2836-peripherals.pdf
- https://github.com/eggman/raspberrypi/tree/master/qemu-raspi2
- https://github.com/eggman/FreeRTOS-raspi3/blob/master/Demo/FreeRTOS_tick_config.c
- https://developer.arm.com/documentation/dui0802/b/A64-General-Instructions/A64-general-instructions-in-alphabetical-order?lang=en
- https://wiki.osdev.org/ARM_RaspberryPi
- https://elinux.org/RPi_Framebuffer
- https://github.com/bztsrc/raspi3-tutorial
- https://github.com/rust-embedded/rust-raspberrypi-OS-tutorials
- // PRIV LEVL: https://developer.arm.com/documentation/den0013/d/ARM-Processor-Modes-and-Registers
- // MODES: https://developer.arm.com/documentation/ddi0406/c/System-Level-Architecture/The-System-Level-Programmers--Model/ARM-processor-modes-and-ARM-core-registers/ARM-processor-modes?lang=en
- // EXCEPTION HANDLING: https://developer.arm.com/documentation/ddi0406/c/System-Level-Architecture/The-System-Level-Programmers--Model/Exception-handling?lang=en
- // MODE REGISTERS: https://developer.arm.com/documentation/ddi0406/c/System-Level-Architecture/The-System-Level-Programmers--Model/ARM-processor-modes-and-ARM-core-registers/ARM-core-registers?lang=en
# Program Status Registers
- https://developer.arm.com/documentation/ddi0406/c/System-Level-Architecture/The-System-Level-Programmers--Model/ARM-processor-modes-and-ARM-core-registers/Program-Status-Registers--PSRs-?lang=en#CIHJBHJA
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