=Electronics Hardware Questions=

Q:
Design a FIFO...

A:
module fifo1 (full,empty,clk,clkb,ain,bout,rst_N)
output [7:0] bout;
input [7:0] ain;
input clk,clkb,rst_N;
output empty, full;
reg [3:0] wptr, rptr;
...

endmodule

wptr -->

0
1
2
3
4
5
6
7
8
9
10
11
12
<-- rptr

Multiple clocks add complexity to this design. We need to define conditions for Empty and Full signals, take care of WR and RD pointers. Here is one of the solutions.

Empty and Full flags:
assign empty=((wptr == rptr) && (w_flag == r_flag);
assign full=((wptr == rptr) && (w_flag == ~r_flag);

where w_flag is set when wptr =12 (end of FIFO). After that wptr is reset to 0. The same for r_flag and rptr.

Pointer handling:
if (wptr == 12) {w_flag,wptr} <= {~w_flag,4'b0000};
else wptr <= wptr+1;
if (rptr == 12) {r_flag,rptr} <= {~r_flag,4'b0000};
else rptr <= rptr+1;