This repository contains an implementation of several C standard library functions in Thumb2 assembly for the Cortex-M microcontroller. This project was undertaken as an exploration of low-level programming, combining C and Thumb2 assembly to build a custom C library.
The Thumb2-Cortex-M project showcases the implementation of various C standard library functions in Thumb2 assembly. The objective was to gain a deeper understanding of how these functions work at the assembly level, while also providing a practical toolkit for use in Cortex-M microcontroller programming. Each implemented function is prefixed with an underscore (_) to distinguish it from the original functions in the C library.
The repository includes the following C standard library functions implemented in Thumb2 assembly:
_bzero: Sets the values of a block of memory to zero._strncpy: Copies a specified number of characters from one string to another._mallocand_free: These are user functions that interact with the SVC handler to call the correspondingprivileged functions,_kallocand_kfree. The latter pair utilizes the buddy memory system for memory allocation and deallocation, using recursion in the form of_rallocand_rfree._signaland_alarm: These functions interact with the SVC handler to call appropriate timer functions for signal handling and timer start, respectively._atoi: This function converts a string into an integer. It was implemented as an extra credit challenge and is not fully functional.
In addition to the C standard library functions, the project also includes:
startup: This script has been modified to call the custom functions appropriately.svc.s: This is where the system call jump table is initialized and used as a function directory.heap.s: This script initializes the Memory Control Block (MCB), which manages the heap's space. It also provides a visual representation of used portions of the heap with a bit in the 0 place.timer.s: This script handles the timer, alarm, and signal handler for system interrupts.