Hardware interview practice
Route a shared read bus without internal tri-states
Design a two-master, one-slave read-bus multiplexer. An external sel chooses the eligible master, only one request may be outstanding, and the response must return to the master that launched it. Add a master BFM read task.
Reviewed example
Work through one case
Input
cycle1 sel=0 and master0 request A handshakes; sel changes to 1 before slave response A at cycle4Expected output
response valid/data route only to master0; master1 response path remains known inactiveThe accepted owner is latched with the request, so a later external selection change cannot misroute the delayed response.
What to cover
Requirements
- Use valid/ready handshakes on requests and an explicit valid on responses.
- Latch the selected owner when the slave accepts a request; sel may change before the response returns.
- Drive inactive response paths to known values rather than high impedance.
- Apply backpressure while a read is outstanding and keep the BFM request stable until accepted.
- The slave response arrives no earlier than the cycle after request acceptance; a zero-latency slave would require an explicit response bypass.