# Mutlithreading for the Tiva C series
This project is a PoC of an ASM multithreading implementation for ARM Thumb
devices.

## Project contents:
* Threading          (pthread.asm)
    * Start thread:  (threadstart)
    * Stop thread:   (threadexit)
    * Thread fencing:
        * Lock       (threadlock)
        * Unlock     (threadunlock)
* Memory management: (malloc.asm)
    * Malloc_init:   (minit)
    * Malloc:        (gtmalloc)
    * Free:          (free)
    * Memcpy:        (memcpy)
    * Memset:        (memset)

## Some notes:
To make use of threading, malloc has to be enabled (to store a thread's stack).
To enable malloc, simply call *minit*. This prepares the first element in the
double-linked list to cover the entire 32KiB heap aside from the memory
allocated for the stack.

The threading system uses the built-in SysTick system to determine how many
instructions each thread is delegated before a thread-switch operation is
triggered. The amount of instructions allowed can be set by changing the
constant *STRST*.

Thread fencing allows a thread to request extra time-frames for itself. As it
stands at the moment, thread-fencing will always be allowed, since it was
designed as a way to making thread-unsafe operations virtually atomic. I would
be **very** hesitant to use thread-fencing, since, if timed incorrectly in, for
example an infinite loop, it could cause the thread to inexplicably take full
control of the processor by always being fenced when a thread-switch is
triggered, thus preventing any switches. This is why I would heavily reccomend
manually setting the SysTick timer value to 0 after unlocking: so that a
successful thread-switch is attempted (in case one was missed when the thread
was locked).

## TODOS:
* Automatic thread-switching after unlock if a switch was missed
* Smarter malloc
* Dynamic thread-count updating
* Faster thread-switching
* Runtime thread-instruction variability

## Tested platforms:
* Tiva C-series
    * TM4C123GH6PM (Evaluation board: TM4C123GXL)