AVR-Processor

VHDL implementation of an 8-bit AVR processor supporting most AVR RISC instructions.

Project Information

Caltech EE 119B Albert Gural and Bryan He

Main Project Files

• The VHDL AVR Implementation is located in ./src/AVR.
• The AVR processor itself is a VHDL entity AVR_CPU.
• A test AVR project is located in ./code-gen/systest.

Tools

• Xilinx ISE (14.7) for the VHDL implementation for an XC3S1200E-4FG320 chip.
• Atmel Studio 6 for creating test code for an ATmega16 chip.
• C++ compiler for various scripts.

Testing

ALU

The test entity is ALU_TEST in the Xilinx ISE project. Test code and simulation can be run from ALU_TEST_TB.

Registers

The test entity is REG_TEST in the Xilinx ISE project. Test code and simulation can be run from REG_TEST_TB.

Memory

The test entity is MEM_TEST in the Xilinx ISE project. Test code and simulation can be run from MEM_TEST_TB.

Full AVR CPU

The test entity is AVR_CPU_TEST in the Xilinx ISE project. Simulation can be run from AVR_CPU_TEST_TB. For convenience, a debug signal (register R16) has been broken out to see whether the implementation successfully passes all programming tests. Also for convenience, the program address bus is broken out.

Modifying the AVR CPU test

The supplied tests validate basic operation of the CPU. It isn't too thorough since previous tests of the ALU, Registers, and Memory are already very thorough. However, if there's a specific test you'd like to run, you can modify the tests by following these steps.

1. Open the AVR project located in ./code-gen/systest.
2. Modify the systest.asm file with updated tests. If the tests fail, you should put an error code (number between 1 and 255) on register R16, then jump to the label Bad. If the tests pass, just proceed with the rest of the tests normally.
3. Compile and run the AVR debugger to ensure the modifications pass all tests.
4. The hex file is located at ./code-gen/systest/systest/Debug/systest.hex.
5. Compile and run .code-gen/hex_to_progmem.cpp (no arguments need to be provided). The file ./code-gen/progmem.out will be modified.
6. Open ./src/AVR/progmem.vhd and replace the program memory it contains with the program memory in ./code-gen/progmem.out.

Disclaimer

This project was meant as a learning experience in CPU architecture and VHDL programming. In no way are we guaranteeing that the processor works as designed, nor that it is even stable! Use at your own risk.