Embedded C Linux Projects

Developed By:

• Adam Pietrewicz
• Hooman Keshvari

A repository for Embedded Linux course projects for the DE1-SoC Development Board.

Skills Demonstrated

• User-level and kernel-level programming in Linux
• Memory-mapped I/O with FPGA peripherals
• Handling hardware interrupts in the Linux kernel
• Writing Makefiles and building kernel modules
• Real-time embedded system design concepts

Project 2: Embedded Linux Programs

Part 1: Scrolling Message

• Linux user-level C program that displays a scrolling message on the 7-segment display and terminal
• Pushbutton keys are used to pause/resume scrolling
• Communicate with SoC hardware through memory-mapped IO

Part 2: Real-time Clock

• A kernel module that displays a real-time clock in the format MM:SS:DD on the 7-segment display and terminal
• Uses FPGA hardware timer register interface to generate periodic interrupts for clock

Part 3: Stopwatch

• A kernel module that acts as a countdown stopwatch displayed as MM:SS:DD
• Can set start time using switches and pushbuttons
• Supports starting, pausing, and resetting the stopwatch via pushbutton interrupts

Project 3: Character Device Drivers

Part 1: Basic Character Device Driver

• Implemented a simple character device driver (chardev) as a Linux kernel module
• Supports read and write operations via /dev/chardev, allowing user programs to modify and retrieve a message

Part 2: Input Drivers for Switches and Pushbuttons

• Created kernel modules providing /dev/KEY and /dev/SW interfaces
• Drivers read the states of DE1-SoC pushbuttons (KEY) and slider switches (SW) and returned their values to the user as ASCII-encoded data

Part 3: Output Drivers for LEDs and 7-Segment Displays

• Developed drivers for controlling LEDs (/dev/LEDR) and 7-segment displays (/dev/HEX)
• Drivers accepted ASCII-encoded input from the user to display patterns and values on the hardware

Part 4: User-Level Control Program

• Wrote a C user-space program to integrate all drivers
• When a KEY was pressed, the current state of the SW switches was displayed on the LEDR lights, and the accumulated total was shown on the HEX displays

Project 4: Using Character Device Drivers

Part 1: Stopwatch Driver

• Implemented a basic stopwatch driver supporting open, release, and read operations
• Displays stopwatch time in terminal via cat /dev/stopwatch

Part 2: Enhanced Stopwatch Driver via Write Commands

• Extended the driver to support write operations, enabling commands:
  • run / stop — start or pause stopwatch
  • MM:SS:DD — set stopwatch time
  • disp / nodisp — enable/disable seven-segment display output

Part 3: User-Level Stopwatch Control Program

• Developed a user-level C program to interact with the stopwatch driver
• Program runs in an endless loop, responding to hardware inputs:
  • KEY0: toggles between run and pause
  • KEY1–KEY3: set stopwatch time parts (MM, SS, DD) using SW switches
  • SW switches: specify the time values
• Read input from KEY and SW device drivers, and optionally displayed SW values on LEDs

Part 4: Interactive Math Game

• A user-level C program that turns the stopwatch into a timed math quiz game
• Presents a series of math questions to answer before time runs out
• Tracks and reports statistics at the end (questions answered, average response time)
• Optionally displays stopwatch on seven-segment display during the game

Project 5: ASCII Graphics for Animation

Part 1: Static ASCII Graphics

• Used VT100 commands to send ASCII escape sequences to the Linux terminal to clear the screen, and draw colored characters at specific positions

Part 2: Line Drawing with Bresenham’s Algorithm

• Implemented Bresenham’s algorithm in C to draw straight lines between two points on the terminal

Part 3: Moving Line Animation

• Extended the program to create a moving horizontal line that bounces vertically
• Implemented basic collision detection with the top and bottom edges of the screen

Part 4: Random Line Animation

• Extended the animation to include multiple objects moving and bouncing off screen edges
• Connected moving objects with lines to form a dynamic “chain"
• Used random initial positions and directions for variety

Part 5: Interactive Animation Enhancements

• Enhanced the Part 4 animation to respond to hardware inputs (KEYs and SW switches) in live-time to:
  • Adjust animation speed up/down
  • Increase/decrease the number of animated objects
  • Toggle drawing of connecting lines on/off

Project 6: Graphics & Animation Using Linux Character Drivers

Part 1: VGA Driver

• Implemented a Linux character device driver (/dev/video) to interface with the VGA display to:
  • Clear the screen
  • Set individual pixel colours

Part 2: Line Drawing Command

• Extended the driver with a line drawing command (Bresenham’s algorithm)
• Reduced overhead by moving line computation into the driver rather than issuing many pixel commands

Part 3: Animation with Synchronization

• Added support for VGA vertical synchronization (sync command) to avoid tearing during animations by performing pixel buffer swapping
• Developed a user-space program to animate a horizontal line bouncing between the top and bottom of the screen

Part 4: Animated Boxes

• Enhanced the driver to support drawing boxes of any specified length
• Wrote a user-level program that animates eight bouncing rectangles, connected by lines to form a moving chain
• Implemented double-buffering for smooth animations without flickering by storing pixel buffers in FPGA on-chip memory and SDRAM

Part 5: Controlling Animated Boxes

• Added user interaction to control the animation using pushbuttons and switches in real time to:
  • Adjust animation speed
  • Increase/decrease the number of rectangles
  • Toggle lines between rectangles on/off

Part 6: VGA Text Display

• Extended the driver to work with the VGA character buffer to display a frame counter in the corner of the screen
• Added commands to:
  • Erase text from the screen
  • Display ASCII text at specified screen coordinates

Project 7: ADXL345 Accelerometer

Part 1: Configuring and Reading the ADXL345

• A user level program that configures the accelerometer, and prints real-time X, Y, Z acceleration values while tilting the board using virtual addresses to access the chip via memory-mapped I/O

Part 2: ADXL345 Character Device Driver

• Developed a character device driver for the ADXL345 to add support to the Linux kernel for accessing the device
• Created /dev/accel device file to allow user-space access to accelerometer data

Part 3: Device Driver Write Operations & Graphical Demo

• Extended the character device driver to handle write commands such as:
  • init: re-initializes the device
  • calibrate: runs calibration routine
  • format F G: sets resolution & range
• Implemented a user-space program with a graphical demo that displays a “bubble” that moves based on board tilt
• Supported smoothing of acceleration readings using a running average to reduce jitter

Part 4: Tap and Double-Tap Detection

• Enhanced the driver to detect tap and double-tap gestures using the ADXL345’s interrupt capabilities

Project 8: Audio and Multithreaded Applications on DE1-SoC

Part 1: Single Tone Playback

• Wrote a Linux user-level C program that generates and plays the middle C chromatic scale through the audio-out port of the DE1-SoC Computer system
• Used memory-mapped I/O to write samples to the DE1-SoC audio CODEC via the audio port registers

Part 2: Chord Playback

• Extended the program to play multiple tones (chords) simultaneously (without volume overflow) based on a 13-character command-line input

Part 3: Digital Piano with Multithreading

• Created a multithreaded digital piano that responds to USB keyboard input in real-time
• Used Pthreads to separate audio generation and input handling, improving responsiveness and timing accuracy

Part 4: Piano Waveform Visualization

• Added a third thread to display the currently played sound waveforms on the VGA screen using character device drivers to communicate with the VGA controller

Part 5: Recording and Playback

• Implemented a feature to record and play back sequences of notes, tracking piano key press/release timings
• Used the stopwatch and pushbuttons/LEDs to control and indicate recording/playback status

Part 6: Character Device Driver Version

• Modified the program to use the Linux character device driver interface (/dev/IntelFPGAUP/audio) instead of memory-mapped I/O for audio output

Project 9: Simple Oscilloscope Using DE1-SoC

Part 1: Reading ADC Pin Voltage

• C program that reads from the DE1-SoC ADC (AD7928) controller port registers and prints the voltage level of the ADC connector pin to the terminal

Part 2: Digital Signal Generator

• Developed a Linux kernel module that generates a configurable square wave on pin D0 of the JP1 connector of the DE1-SoC
• Used FPGA Timer0 to generate periodic interrupts and toggle the output pin at a frequency set by board switches (10–160 Hz)
• Displayed the selected frequency and switch settings on LEDs and seven-segment displays

Part 3: Oscilloscope Application

• Wrote a C program that implements an oscilloscope that samples ADC channel 0 periodically and displays the waveform on the VGA screen
• Triggered sweeps on rising or falling edges of the input signal based on switch SW0

Part 4: Enhanced Oscilloscope With Sweep Time Control

• Enhanced the oscilloscope to allow the user to adjust the sweep duration using the board’s KEY buttons (increase/decrease by 100 ms increments)

Project 10: Image Processing: Canny Edge Detection

Part 1: Software Implementation

• Developed an implementation of the Canny Edge Detection Algorithm in C which includes: grayscale conversion, Sobel operator, non-max suppresison and hysteresis
• tested edge detection on BMP images and visualized results using VGA display

Part 2: Hardware Setup and Image Display

• Reconfigured the FPGA with a hardware edge-detection system
• Wrote C function to properly pack 24-bit pixels into 32-bit SDRAM memory
• Implemented flip() that flips the image vertically before writing it into the SDRAM buffer so it appears correctly on the video output

Part 3: Hardware-Accelerated Edge Detection

• Extended the Part 2 code to enable and control the FPGA’s hardware edge-detection pipeline
• Used DMA controllers and their registers to:
  • Stream image data to and from the FPGA-based edge-detection circuit
  • Swap buffer addresses and wait for completion using status polling
  • Display the edge-detected output on the VGA monitor
  • Saved the hardware-processed edge-detected image back to a BMP file
• Compared the hardware-accelerated runtime against the CPU-only implementation to evaluate performance improvements