//----------------------------------------------------
// A four level, round-robin arbiter. This was
// orginally coded by WD Peterson in VHDL.
//----------------------------------------------------
module arbiter (
clk,
rst,
req3,
req2,
req1,
req0,
gnt3,
gnt2,
gnt1,
gnt0
);
// --------------Port Declaration-----------------------
input clk;
input rst;
input req3;
input req2;
input req1;
input req0;
output gnt3;
output gnt2;
output gnt1;
output gnt0;
//--------------Internal Registers----------------------
wire [1:0] gnt ;
wire comreq ;
wire beg ;
wire [1:0] lgnt ;
wire lcomreq ;
reg lgnt0 ;
reg lgnt1 ;
reg lgnt2 ;
reg lgnt3 ;
reg lasmask ;
reg lmask0 ;
reg lmask1 ;
reg ledge ;
//--------------Code Starts Here-----------------------
always @ (posedge clk)
if (rst) begin
lgnt0 <= 0;
lgnt1 <= 0;
lgnt2 <= 0;
lgnt3 <= 0;
end else begin
lgnt0 <=(~lcomreq & ~lmask1 & ~lmask0 & ~req3 & ~req2 & ~req1 & req0)
| (~lcomreq & ~lmask1 & lmask0 & ~req3 & ~req2 & req0)
| (~lcomreq & lmask1 & ~lmask0 & ~req3 & req0)
| (~lcomreq & lmask1 & lmask0 & req0 )
| ( lcomreq & lgnt0 );
lgnt1 <=(~lcomreq & ~lmask1 & ~lmask0 & req1)
| (~lcomreq & ~lmask1 & lmask0 & ~req3 & ~req2 & req1 & ~req0)
| (~lcomreq & lmask1 & ~lmask0 & ~req3 & req1 & ~req0)
| (~lcomreq & lmask1 & lmask0 & req1 & ~req0)
| ( lcomreq & lgnt1);
lgnt2 <=(~lcomreq & ~lmask1 & ~lmask0 & req2 & ~req1)
| (~lcomreq & ~lmask1 & lmask0 & req2)
| (~lcomreq & lmask1 & ~lmask0 & ~req3 & req2 & ~req1 & ~req0)
| (~lcomreq & lmask1 & lmask0 & req2 & ~req1 & ~req0)
| ( lcomreq & lgnt2);
lgnt3 <=(~lcomreq & ~lmask1 & ~lmask0 & req3 & ~req2 & ~req1)
| (~lcomreq & ~lmask1 & lmask0 & req3 & ~req2)
| (~lcomreq & lmask1 & ~lmask0 & req3)
| (~lcomreq & lmask1 & lmask0 & req3 & ~req2 & ~req1 & ~req0)
| ( lcomreq & lgnt3);
end
//----------------------------------------------------
// lasmask state machine.
//----------------------------------------------------
assign beg = (req3 | req2 | req1 | req0) & ~lcomreq;
always @ (posedge clk)
begin
lasmask <= (beg & ~ledge & ~lasmask);
ledge <= (beg & ~ledge & lasmask)
| (beg & ledge & ~lasmask);
end
//----------------------------------------------------
// comreq logic.
//----------------------------------------------------
assign lcomreq = ( req3 & lgnt3 )
| ( req2 & lgnt2 )
| ( req1 & lgnt1 )
| ( req0 & lgnt0 );
//----------------------------------------------------
// Encoder logic.
//----------------------------------------------------
assign lgnt = {(lgnt3 | lgnt2),(lgnt3 | lgnt1)};
//----------------------------------------------------
// lmask register.
//----------------------------------------------------
always @ (posedge clk )
if( rst ) begin
lmask1 <= 0;
lmask0 <= 0;
end else if(lasmask) begin
lmask1 <= lgnt[1];
lmask0 <= lgnt[0];
end else begin
lmask1 <= lmask1;
lmask0 <= lmask0;
end
assign comreq = lcomreq;
assign gnt = lgnt;
//----------------------------------------------------
// Drive the outputs
//----------------------------------------------------
assign gnt3 = lgnt3;
assign gnt2 = lgnt2;
assign gnt1 = lgnt1;
assign gnt0 = lgnt0;
endmodule
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