Transcript N64 overview - EECS @ University of Michigan

Limited wires.
• We have only one data
line. Use for for bidirectional
communication.
• Need to send:
– requests for data
– rumble pack on/off
• Need to receive
– controller status
Some slides from Aaron Ridenour, Ryan Wooster and Alex Jaeckel. http://www.eecs.umich.edu/courses/eecs373/Lec/F13Student/N64.pptx
See http://www.eecs.umich.edu/courses/eecs373/Lec/StudentW14/N64%20Controller.pdf for other details.
Bi-directional Open Collector
• Pull-up resistor keeps the line high while idle.
• To send 0, the output line is pulled low and
connected to ground.
• To send 1, nothing should be sent.
• Never drive the line high.
• Both sides do this, so bidirectional.
– If no data to send, wire stays (floats) high.
Controller Encoding
Logical 0:
Each bit is sent in ~4 𝜇𝑠
Low for 3 𝜇𝑠, followed
by high for 1 𝜇𝑠
Logical 1:
Low for 1 𝜇𝑠, followed
by high for 3 𝜇𝑠
Controller Encoding
http://inst.eecs.berkeley.edu/~cs150/sp01/Labs/lablecckpt1.ppt
|----Command (console) 0x01-----|
0 L R
|----Data1 (controller) 0x00------||-------Data2 (controller) 0x00----|
Joystick y-coordinate
stop bit
Joystick x-coordinate
reset
start bit
A B Z S
t
|--------Data3 (controller) 0x00----------||---------Data4 (controller) 0x01-----------|
Images taken from: http://afermiano.com/index.php/n64-controller-protocol
Clock Synchronization
• Once a FF goes metastable (due to a setup time
violation, say) we can’t say when it will assume a
valid logic level or what level it might eventually
assume.
• The only thing we know is that the probability of a
FF coming out of a metastable state increases
exponentially with time.
This and next slide from http://web.stanford.edu/class/ee183/handouts/synchronization_pres.pdf. If you have an interest in this topic, that’s a nice slide set.
https://web.archive.org/web/20070203054100/http://www.caip.rutgers.edu/~bushnell/dsdwebsite/dsdlecture18.ppt has yet more details.
Traditional synchronizer
• SIG is asynchronous, and META might go metastable
from time to time
• However, as long as META resolves before the next
clock period SIG1 should have valid logic levels
• Place FFs close together to allow maximum time for
META to resolve.
– Under reasonable assumptions, MTBF=9x1010 years.
– More than the age of the Earth. Could add a third.