1. System-on-Chip Design Principles of Hardware/Software Communication
Hao Zheng
Comp Sci & Eng
U of South Florida

2. System Structural Model
CPU
Mem P1 P2
Arbiter
Bridge P3 P5 P4 HW HW

3. Basic Elements of HW/SW Interfaces

4. Synchronization Schemes
Synchronization is necessary for effective communications

5. Synchronization Schemes

6. Semaphores Used to control of accesses to shared resource.
Two ops on semaphore S:
P(S): acquire S.
V(S): release S.
thread 1: …
P(S);
x++;
V(s);
thread 2: …
P(S);
x = x – 2;
V(s);

7. Semaphores entity two { entity one { short_delay(); P(S); while (1) {
rd = shared_data; }}
entity one {
P(S);
while (1) {
short_delay();
shared_data = …;
V(S); }}
int shared_data;
semaphore S;

8. Semaphores
Semaphores can only guarantee exclusive access to shared resources.
difficult to control precise data transfer
Multiple semaphores can be used, but not elegant.
Handshaking: a signaling protocol between two entities to coordinate data transfers.
Can handle entities with different speeds.

9. One-Way Handshake

10. Two-Way Handshake

11. Two-Way Handshake for Data Transfer
req
ack
Dest
Src
data
clk
req
ack X X
data X X X X X X X d1

12. Communication Constrained vs Computation Constrained
System performance should consider both computation performance and communication overhead.

13. Communication Constrained vs Computation Constrained

14. Tight and Loose Coupling
Coupling: the degree of interactions between two components

15. Dedicated vs Shared Interfaces
Nature of coupling affects the organization of HW/SW interfaces
tight coupling
loose coupling

16. Reading Guide
Chapter 9, the CoDesign book.