Stack Computers: 5.1 WHY 32-BIT SYSTEMS?

Chapter 5. Architecture of 32-bit Systems

5.1 WHY 32-BIT SYSTEMS?

The 16-bit processors described in Chapter 4 are sufficiently powerful for a wide variety of applications, especially in an embedded control environment. But, there are some applications that require the added power of a 32-bit processor. These applications involve extensive use of 32-bit integer arithmetic, large memory address spaces, or floating point arithmetic.

One of the difficult technical challenges that arises when designing a 32-bit stack processor is the management of the stacks. A brute force approach is to have separate off-chip stack memories in the manner of the NC4016. Unfortunately, on a 32-bit design this requires having 64 extra pins for just the data bits, making the approach unpractical for cost-sensitive applications. The FRISC 3 solves this problem by maintaining two automatically managed top-of-stack buffers on-chip, and using the normal RAM data pins to spill individual stack elements to and from program memory. The RTX 32P simply allocates a large amount of chip space to on-chip stacks and performs block moves of stack elements to and from memory for stack spilling. Chapter 6 goes into more detail about the tradeoffs involved with these approaches.

NEXT NEXT SECTION

Phil Koopman -- koopman@cmu.edu