Stack Pointer Up Down Control
Memory-based stacks require precise pointer arithmetic to track the top of the stack dynamically. Off-by-one errors in pointer management cause complete system crashes.
The stack pointer sp tracks the next empty location in memory. This requires a post-increment operation for pushes and a pre-decrement operation for pops. The combinational output addr provides the correct memory address for the current operation, while the 4-bit register sp updates on the next rising clock edge.
| rst | push | pop | addr (Current Cycle) | sp (Next Cycle) | |-------|--------|-------|------------------------|-------------------| | 1 | X | X | 0 | 0 | | 0 | 0 | 0 | sp | sp | | 0 | 1 | 0 | sp | sp + 1 | | 0 | 0 | 1 | sp - 1 | sp - 1 | | 0 | 1 | 1 | sp - 1 | sp |
Constraints
- Implement synchronous active-high reset logic.
- The
spandaddroutputs must be exactly 4 bits wide. - Use 4-bit wrap-around arithmetic for pointer updates. No overflow or underflow flags are required.
Topics
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