FIFO Almost Full Warning Logic
High-speed data links and streaming processors rely on flow control to prevent data loss. A FIFO almost-full flag provides critical lead time for an upstream transmitter to pause traffic before the buffer overflows.
The circuit evaluates the current 3-bit read pointer (rd_ptr) and 3-bit write pointer (wr_ptr) of an 8-entry circular buffer. The almost_full output must assert high exactly when the write pointer is two slots away from catching up to the read pointer. Because the buffer is circular, this calculation must account for modulo-8 wraparound.
| rd_ptr | wr_ptr | almost_full | |----------|----------|---------------| | 2 | 0 | 1 | | 3 | 0 | 0 | | 1 | 7 | 1 | | 0 | 6 | 1 |
Constraints
- Combinational logic only.
- Do not use any sequential elements or clocks.
Topics
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