This tutorial provides and describes verilog to allow the DE1-SoC FPGA board to interface with a PS/2 mouse. The PS/2 mouse controller module supports three button inputs - left click, right click, and middle click - along with mouse movements in the X (horizontal) and Y (vertical) directions.
The design interfaces with the DE1-SoC's PS/2 port, so a USB mouse will require a small inexpensive USB-to-PS/2 converter.
The verilog code provided comprises two files: the mouse controller module and a testbench module to quickly and easily get the mouse working.
The mouse module can be placed into a top-level module or submodule with access to the PS/2 ports and a 50 MHz clock. Two additional control signals need to be connected for START and RESET functionality.
The mouse controller module has the following inputs, outputs, and inouts:
iSTART – input, active xxxx, for transmitting instructions to device
iRST_n – input, active low?, FSM reset signal
iCLK_50 – input, 50 MHz clock signal from DE1-SoC
PS2_CLK – inout, for ps2_clock signal to/from the PS2 device
PS2_DAT – inout, for ps2_data signal to/from the PS2 device
oLEFBUT – output, active high, left mouse button press
oMIDBUT – output, active high, middle mouse button press
oRIGBUT – output, active high, right mouse button press
oX[7:0] – output, active xxxx, mouse horizontal displacement
oY[7:0] – output, active xxxx, mouse vertical displacement
Mouse displacement signals oX and oY are encoded as 8-bit unsigned values that "wrap" when the value exceeds 255 or drops below zero.
The PS/2 port utilizes two wires for bi-directional communication to send initialization signals to the device and return mouse command data to the board.
Select the PS/2 option when generating a pin assignment file using the DE1-SoC SystemBuilder. The generated top level module contains two pairs of "inout PS2_*" ports: PS2_DAT, PS2_DAT2, PS2_CLK, and PS2_CLK2. The mouse.v module utilizes the pair of signals without a "2" at the end of their names.
Use of the PS/2 port requires the PS/2 option to be selected when generating a pin assignment file using the DE1-SoC SystemBuilder program. Once the assignment is generated, the corresponding top level module contains two sets of "inout" DATA and CLOCK ports, named PS2_DAT, PS2_DAT2 and PS2_CLK, PS2_CLK2 respectively, as the PS/2 standard supports both a mouse and keyboard using a physical adapter. This module only utilizes the first set of ports as the controller only supports mouse functionality.
When implementing PS/2 Mouse functionality, ensure the PS/2 pin assignments are included when generating a pin assignment file with the SystemBuilder and the PS/2 inout ports are included in the top-level module ports.
The Testbench module is intended to be placed into a top-level module with KEY[1], KEY[0], and SW[0] used for control signal input and data outputs going to the LEDR and HEX devices on the DE1-SoC. The left, middle, and right mouse button clicks will be displayed on segment 0 of HEX2, HEX1, and HEX0, respectively. LEDR[7:0] will display the raw mouse displacement data with SW[0] selecting which axis is shown. When SW[0] is high, the Y (vertical) axis is displayed. When SW[0] is low, the X (horizontal) axis is displayed.
The Testbench module can be instantiated in a top-level module with the following:
mouse_test U1 ( .iKEYS (KEY[1:0]), .iSW0 (SW[0]), .iCLK_50 (CLOCK_50), .ioPS2_CLK (PS2_CLK), .ioPS2_DAT (PS2_DAT), .oHEX0 (HEX0), .oHEX1 (HEX1), .oHEX2 (HEX2), .oLEDR (LEDR[7:0]) );
The testbench module has the following inputs and outputs:
iKEYS - KEY[1:0] -> Push buttons for reset/instruction transmission
--> KEY[1] configured as reset
--> KEY[0] configured as instruction transmission
iSW0 - SW[0] -> SW to determine if X or Y movement value is shown on LEDR
ioPS2_CLK - PS2_CLK -> clock inout signal for PS2 mouse device
ioPS2_DAT - PS2_DAT -> data inout signal for PS2 mouse device
oHEX0 - HEX0 -> 7-Segment output used to show Right Mouse Button click
oHEX1 - HEX1 -> 7-Segment output used to show Middle Mouse Button click
oHEX1 - HEX1 -> 7-Segment output used to show Left Mouse Button click
oLEDR - LEDR[7:0] -> LEDR output used to show X/Y movement value
Another reference design can be found here: http://www-ug.eecg.utoronto.ca/desl/MSO_de1_tutorials.html at a website at the University of Toronto.
2022/06/08 Written 2024/04/15 Re-written Author: Derek Li