Interview Question 22: Micro Architect a Block

You are asked to micro-architect this block. The goal is to keep performance high enough to keep Encryption Engine busy all the time.

Assumptions:

- External memory (DDR) has 16Gbps bandwidth but 45 clocks latency

- DMA description memory has 6 clocks of latency and needs 6 clocks to fetch the whole descriptor.

- Encryption engine provides data in next clock.

This question shows the experience and maturity of the designer. The key concepts which one should look for are

- Latency

- Performance

- Pipelining of memory operations

- FIFO sizing

- State Machines etc