Lab 4: High level I/O - VGA, PS/2 Keyboard, and Audio

Lab 4: High level I/O - VGA, PS/2 Keyboard, and Audio
ECSE 324 - Computer Organization

Introduction
In this lab will use the high level I/O capabilities of the DE1-SoC computer. In particular, the tasks
will:
• Use the VGA controller to display pixels and characters.
• Use the PS/2 port to accept input from a keyboard
• Use the audio controller to play generated tones
1
1 VGA
For this part, it is necessary to refer to section 4.2 (pp 40-43) of the De1-SoC Computer Manual.
Brief overview of the De1-SoC computer VGA interface
The VGA controller hardware has already been introduced in the ECSE 222 labs. The De1-SoC
computer has a built in VGA controller, and the data displayed to the screen is acquired from two
sections in the FPGA on-chip memory - the pixel buffer and the character buffer - which are described
in sufficient detail in section 4.2.1 and 4.2.3 of the De1-SoC Computer Manual. For this lab, it is not
required to make use of the double buffering feature described in the manual.
VGA driver
Create two files VGA.s and VGA.h and place them in the correct folders. The code for the header
file is shown in Figure 1.
Figure 1: Code for the VGA.h file
The subroutines VGA clear charbuff ASM and VGA clear pixelbuff ASM should clear (set to 0) all
the valid memory locations in the character buffer and pixel buffer respectively.
VGA write char ASM should write the ASCII code passed in the third argument to the screen at
the (x,y) coordinates given in the first two arguments. Essentially, the subroutine will store the value
of the third argument at the address calculated with the first two arguments The subroutine should
check that the coordinates supplied are valid (i.e. x = [0,79] and y = [0,59]).
VGA write byte ASM should write the hexadecimal representation of the value passed in the third
argument to the screen. This means that this subroutine will print two characters to the screen! (For
example, passing a value of 0xFF in byte should result in the characters ’FF’ being displayed on the
screen starting at the x,y coordinates passed in the first two arguments) Again, check that the x and
y coordinates are valid, taking into account that two characters will be displayed.
Both the above subroutines should only access the character buffer memory.
Finally, the VGA draw point ASM subroutine will draw a point on the screen with the colour as
indicated in the third argument, by accessing only the pixel buffer memory. This subroutine is very
similar to the VGA write char ASM subroutine
2
NOTE: Use suffixes ‘B’ and ‘H’ with the assembly memory access instructions in order to
read/modify bytes/half-words
Simple VGA application
Build a C based application to test the functionality of the VGA driver. Write three functions as
shown in Figure 2
Figure 2: C functions used to test the VGA driver
Use the pushbuttons and slider switches as follows:
• PB0 is pressed: if any of the slider switches is on, call the test byte() function, otherwise, call
the test char() function.
• PB1 is pressed: call the test pixel() function.
• PB3 is pressed: clear the character buffer.
• PB4 is pressed: clear the pixel buffer.
3
2 Keyboard
For this part, it is necessary to refer to section 4.5 (pp 45-46) in the De1-SoC Computer Manual.
Brief overview of the PS/2 Keyboard Protocol
For the purpose of this lab, a very high level description of the PS/2 keyboard protocol is given. A
more detailed description can be found at this link.
The PS/2 bus provides data about keystroke events by sending hexadecimal numbers called scan
codes, which for this lab will vary from 1-3 bytes in length. When a key on the PS/2 keyboard is
pressed, a unique scan code called the make code is sent, and when the key is released, another
scan code called the break code is sent. The scan code set used in this lab can be found here.
Two other important parameters involved are the typematic delay and the typematic rate. When
a key is pressed, the corresponding make code is sent, and if the key is held down, the same make
code is repeatedly sent at a constant rate after an initial delay. The make code will stop being
sent only if the key is released or another key is pressed. The initial delay between the first and
second make code is called the typematic delay, and the rate at which the make code is sent after
this is called the typematic rate. The typematic delay can range from 0.25 seconds to 1.00 second
and the typematic rate can range from 2.0 cps (characters per second) to 30.0 cps, with default
values of 500 ms and 10.9 cps respectively.
(a) Key ’a’ is pressed and released
(b) Key “a” is pressed, held down, and then released
Figure 3: Example of data received on the PS/2 bus
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PS/2 keyboard driver
Create two files ps2 keyboard.s and ps2 keyboard.h and place them in the correct folders.
For this lab, simply implement a subroutine with the following specifications:
• Name: read PS2 data ASM
• Argument: A char pointer variable data, in which the data that is read will be stored
• Return type: Integer that denotes whether the data read is valid or not
• Description: The subroutine will check the RVALID bit in the PS/2 Data register. If it is
valid, then the data from the same register should be stored at the address in the char pointer
argument, and the subroutine should return 1 to denote valid data. If the RVALID bit is not
set, then the subroutine should simply return 0.
Simple keyboard application
Create a simple application that uses the PS/2 keyboard and VGA monitor. The application should
read raw data from the keyboard and display it to the screen if it is valid. Only the VGA write byte ASM
subroutine is needed from the VGA driver, and the input byte is simply the data read from the keyboard.
Note: In the program, keep track of the x,y coordinates where the byte is being written.
For example, write the first byte at (0,0) and the second byte at (3,0) and so on until the first
line on the screen is full, and then start writing bytes at (0,1), (3,1), (5,1) etc. A gap of 3 x
co-ordinates is given since each byte will display two characters, and one more for a space
between each byte.
3 Audio
For this part, it is necessary to refer to section 4.1 (pp 39-40) of the De1-SoC Computer Manual
Write a driver for the audio port following the same procedure introduced so far. The driver
should only have one subroutine. The subroutine should take one integer argument and write it to
both the left and the write FIFO only if there is space in both the FIFOs (Hint: Use the value of
WSLC and WSRC in the subroutine). The subroutine should return an integer value of 1 if the data
was written to the FIFOs, and return 0 otherwise.
Use the driver in an application that plays a 100 Hz square wave on the audio out port. The
frequency can be achieved by knowing the sampling rate of of the audio DAC. For example, if the
sampling rate is 100 samples per second and a 2 Hz square wave is to be played, that means there
are two complete cycles of the wave contained in 100 samples, so for 25 samples a ‘1’ should be
written to the FIFOs, and for 25 samples a ‘0’ should be written to the FIFOs.
For this lab, find the sampling rate from the manual and calculate the number of samples for
each half cycle of the square wave. Finally, write 0x00FFFFFF and 0x00000000 to the FIFO instead
of ‘1’ and ‘0’.
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4. Grading
The TA will ask you to demo the following deliverables:
• VGA (60%)
• P/2 Keyboard (40%)
Demos are worth 80% of the lab work, 20% goes toward the lab report.
This lab will last two weeks, however, it is shorter than original one, such that you can have
extra time for demoing Lab3.
Lab report is due one week after the lab is finished.