Pegasus/Picoblaze Calculator

The purpose of this exercice is to get you acquitted with the process of integrating, compiling and synthetising microcontroller IP components. The task is to build a simple calculator for the Pegasus/Picoblaze platform.

Platform

The hardware/software platform for this exercice is comprised by several different items:

• The Pegasus Spartan-II Board:
This board from Digilent Inc. has a built-in Spartan-II FPGA from Xilinx, a configuration ROM, and several peripherals (8 switches, 4 pushbuttons, 4 SSDs and 8 LEDs). You'll probably want to take a look at the manual.
• The Picoblaze IP Component
This VHDL component contains the implementation for the Picoblaze soft-processor. The Picoblaze appnote contains information regarding implementation, usage and functionality (registers, instruction set, etc).
• The Pegasus/Picoblaze system
This is an implementation of a Picoblaze microcontroller environment for the Pegasus board. It is comprised by several elements:
• kcpsm.vhd and embedded_kcpsm.vhd
These are the files that define the Picoblaze processor and connect it to the program ROM memory.
• PROG_ROM.VHD
This is the program memory definition file. It is generated by the Picoblaze assembler.
• seven_segment_display.vhd
This component performs automatic conversion of hexadecimal values to SSD codes.
• pegasus_picoblaze.vhd
This is the top component for this implementation, and connects the Picoblaze to the Pegasus board's peripherals.
• pegasus.ucf
This is a constraints file that specifies the actuals pins connecting the FPGA to the Pegasus peripherals in this system.
• The Picoblaze Assembler
• The Xilinx ISE Platform

Implementation

In this development flow, you need to generate hardware as well as software. Each time you build a new application and assemble it with the Picoblaze assember, you will have a new .vhd file that contains the memory definitions for your application. With this new definition, you will run through the synthesis process through ISE Project Manager, and implement it in the Pegasus Board by downloading the new bitfile into the FPGA with ISE Impact

Functionality

For this exercice, you will implement a simple calculator for the Picoblaze/Pegasus system, for which the following functionalities are required:

• Operand inputs are determined by hexadecimal value presented by the switches. The current switches value is presented in the SSDs, except when a result is requested. An operand is read when an operation is selected.
• A sum (+) operation is selected by button 0. When a sum operation is selected, the current switches value is read and added to the current result.
• A subtraction (-) operation is selected by button 1. When a subtraction operation is selected, the current switches value is read and subtracted from the current result.
• Button 2 resets the result register.
• While Button 3 is pressed, the current result is presented in the SSDs.
• LED 0 signalizes a negative result.
• LED 7 signalizes overflow.

In the first version, the result register is 8-bit wide. In the final version, it must be 16-bit wide.

Solution

• ASM