1. 1. Encode binary value using PCM
How accurate can you get? (+/- 1 usec?)
CSE 477
Design Problems

2. 2. Timer/Interrupt Examples: Timestamp Input Events
Keep a queue of input events
Each event is a timestamp
CSE 477
Design Problems

3. 3. Stepper Motor Control Simple idea
(Timing of signals is important: Acceleration/Deceleration)
CSE 477
Design Problems

4. 4. Serial Communications
Sample the data bits at the right time
Can you adapt to the current data rate?
CSE 477
Design Problems

5. Graphics Intro/Overview
Each location in memory corresponds to one pixel on the display
A process reads the memory and sends the value to the memory at the right time
The memory is called a “frame buffer”
CSE 477
Design Problems

6. Frame Buffer
To display something, just write values into the frame buffer
The display happens automatically
The frame buffer memory is “dual-ported”
i.e. shared between two independent processes
Hardware assist for drawing objects
reduces bandwidth and computation
e.g. lines, rectangles, characters, triangles, ...
CSE 477
Design Problems

7. Double-Buffering What if the image changes from one frame to the next?
Use two frame buffers: change one while the other displays
then switch
CSE 477
Design Problems

8. Double-Buffering Redraw everything on the screen, every frame
Lots of computation
CSE 477
Design Problems

9. Double-Buffering Changing the display 1. Erase and redraw every frame
2. Erase what changes and redraw
Overlap?
CSE 477
Design Problems

10. Drawing Objects e.g. Lines Bresenham’s algorithm Forward differencing
Fast: add/subtract
pixel/clock
No accumulated error
CSE 477
Design Problems

11. Windowing Display only a part of the frame buffer
e.g. fast panning, scrolling
CSE 477
Design Problems

12. Zoom/Shrink e.g. Zoom by 2x Cheap/fast hack
extend to 1.25x?
extend to .75x?
Cheap/fast hack
Works OK for some applications
not images
CSE 477
Design Problems

13. Rotations Very similar to line drawing Fast, cheap transformation
CSE 477
Design Problems

14. Color Map Maps each value in memory to a value for the display
e.g. color transformation (3,3,2) -> (2,2,2)
e.g. binary image planes
Use each bit to represent one color
Overlapping colors defined by color map
Mask a plane (color) by changing the color map
e.g. 4 bit image planes
Two images - switch between them by changing the color map
CSE 477
Design Problems

15. Sprites Objects display over the background
check origin values to decide what to display
transparency?
CSE 477
Design Problems

16. VGA Timing
CSE 477
Design Problems

17. One Frame Vertical Synch tells the monitor when to go back to the top
The Blanking Interval turns off the video at the top and bottom of the screen
CSE 477
Design Problems

18. One Line Each frame is divided into many lines
Horizontal synch tells the monitor to go back to the start of the next line
Each line is divided into pixels
No timing signal: just change the value from one pixel to the next
CSE 477
Design Problems

19. Using a 24 MHz clock Line: 31.77 usec x 24 MHz = 762 clocks/line
Frame: msec x 24 MHz = 402,816 clocks/frame (!)
402,816 / 762 clocks/line = 528 lines
But:
we display 512 pixels/line
480 lines/frame
The rest of the time?
Blanking
Syncs
CSE 477
Design Problems

20. VGA Interface Simple counting will work! VGA interface supplies X, Y
User supplies pixel value
one/clock
CSE 477
Design Problems

21. Design Problem: Complete the VGA interface design
Sketch design for frame buffer memory
VGA supplies address
Reads one port of memory
There should be another port for writing (and reading)
Design the dual-ported memory
CSE 477
Design Problems