FIFO

ROHD-HCL comes with a simple FIFO (First In, First Out). The detailed API docs are available here.

The underlying implementation uses a flop-based memory (see RegisterFile) to store data until it is ready to be popped, with independent read and write pointers.

When writeEnable is high, writeData is added to the FIFO. When readEnable is high, readData is popped off the FIFO.

The FIFO has a configurable depth.

Peeking

When readEnable is low, the readData continually provides access to "peek" the next data.

Empty and Full

The empty signal indicates when nothing is in the FIFO. The full signal indicates when the FIFO can store no additional data.

Bypass

The FIFO optionally supports a bypass if generateBypass is set. When generated, if the FIFO is empty and both readEnable and writeEnable are high at the same time, then the FIFO will do a bypass of the internal storage, allowing for a combinational passthrough.

Errors

Error information can optionally be generated and provided if generateError is set. If data is popped when the FIFO is empty, or pushed when the FIFO is full, then the error signal will assert.

There is no guarantee that the error signal will hold high once asserted. Behavior after an error condition is undefined.

Occupancy

Occupancy information can optionally be generated and provided if generateOccupancy is set. The occupancy signal will indicate the number of items currently stored in the FIFO.

Initial Values

If desired, the initialValues argument can be used to pre-load the FIFO with data upon reset. The length of initialValues must be less than or equal to the depth of the FIFO.

Example Schematic

An example schematic for one configuration is viewable here: FIFO Schematic

Testbench Utilities

The FIFO comes with both a checker and a tracker that you can leverage in your testbench.

Checker

The FifoChecker is a ROHD-VF component which will watch for proper usage of a FIFO in your simulation. It is intended to check usage, not the internal workings of the FIFO, which are already pre-validated in the unit tests. This means it covers things like underflow, overflow, and that the FIFO is empty at the end of the test.

Tracker

The FifoTracker will generate log files using the Tracker from ROHD-VF in either table or JSON format. It tracks reads and writes per timestamp, including data pushed/popped and the current occupancy. An example table is shown below (from one of the unit tests):

----------------------------------------
 | T        | C  | D              | O | 
 | I        | O  | A              | C | 
 | M        | M  | T              | C | 
 | E        | M  | A              | U | 
 |          | A  |                | P | 
 |          | N  |                | A | 
 |          | D  |                | N | 
 |          |    |                | C | 
 |          |    |                | Y | 
----------------------------------------
 |       55 | WR |        32'h111 | 1 | {Time: 55, Command: WR, Data: 32'h111, Occupancy: 1}
 |       75 | WR |        32'h222 | 2 | {Time: 75, Command: WR, Data: 32'h222, Occupancy: 2}
 |       75 | RD |        32'h111 | 1 | {Time: 75, Command: RD, Data: 32'h111, Occupancy: 1}
 |       85 | RD |        32'h222 | 0 | {Time: 85, Command: RD, Data: 32'h222, Occupancy: 0}