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Arbiters.bsv
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Arbiters.bsv
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/* =========================================================================
*
* Filename: Arbiters.bsv
* Date created: 05-09-2011
* Last modified: 05-09-2011
* Authors: Michael Papamichael <papamixATcs.cmu.edu>
*
* Description:
* Implements static priority and round-robin arbiters.
*
* =========================================================================
*/
import Vector::*;
import Arbiter::*;
/////////////////////////////////////////////////////////////////////////
// Encoder
function Maybe#(Bit#(m)) encoder( Vector#(n, Bool) vec )
provisos(Log#(n, m));
Maybe#(Bit#(m)) choice = Invalid;
//for(Integer i=0; i < valueOf(n); i=i+1) // I want the highest to have highest priority
for(Integer i=valueOf(n)-1; i >= 0; i=i-1) // I want the lowest to have highest priority
begin
if(vec[i]) begin
choice = Valid(fromInteger(i));
end
end
return choice;
endfunction
/////////////////////////////////////////////////////////////////////////
// Static Priority Arbiter
// Given a bitmask that has a some bits toggled, it produces a same size
// bitmask that only has the least-significant bit toggled. If no bits
// were originally toggled, then result is same as input.
function Maybe#(Vector#(n, Bool)) static_priority_arbiter_onehot_maybe( Vector#(n, Bool) vec );
Vector#(n, Bool) selected = unpack(0);
Maybe#(Vector#(n, Bool)) result = Invalid;
//for(Integer i=0; i < valueOf(n); i=i+1) // I want the highest to have highest priority
for(Integer i=valueOf(n)-1; i >= 0; i=i-1) // I want the lowest to have highest priority
begin
if(vec[i]) begin
selected = unpack(0);
selected[i] = True; //Valid(fromInteger(i));
result = tagged Valid selected;
end
end
return result;
endfunction
/////////////////////////////////////////////////////////////////////////
// Static Priority Arbiter
// Given a bitmask that has a few bits toggled, it produces a same size
// bitmask that only has the least-significant bit toggled. If no bits
// were originally toggled, then result is same as input.
function Vector#(n, Bool) static_priority_arbiter_onehot( Vector#(n, Bool) vec);
Vector#(n, Bool) selected = unpack(0);
//Maybe#(Bit#(m)) choice = Invalid;
//for(Integer i=0; i < valueOf(n); i=i+1) // I want the highest to have highest priority
for(Integer i=valueOf(n)-1; i >= 0; i=i-1) // I want the lowest to have highest priority
begin
if(vec[i]) begin
selected = unpack(0);
selected[i] = True; //Valid(fromInteger(i));
end
end
return selected;
endfunction
/////////////////////////////////////////////////////////////////////////
// Static Priority Arbiter that starts at specific bit
// Given a bitmask that has a few bits toggled, it produces a same size
// bitmask that only has the least-significant bit toggled. If no bits
// were originally toggled, then result is same as input.
function Vector#(n, Bool) static_priority_arbiter_onehot_start_at( Vector#(n, Bool) vec, Integer startAt);
Vector#(n, Bool) selected = unpack(0);
//Maybe#(Bit#(m)) choice = Invalid;
//for(Integer i=0; i < valueOf(n); i=i+1) // I want the highest to have highest priority
Integer cur = startAt;
for(Integer i=valueOf(n)-1; i >= 0; i=i-1) // I want the lowest to have highest priority
begin
if(vec[cur%valueOf(n)]) begin
selected = unpack(0);
selected[cur%valueOf(n)] = True; //Valid(fromInteger(i));
end
cur = cur+1;
end
return selected;
endfunction
//---------------------------------------------------------------------
// Parameterizable n-way priority encoder.
//
// If the "en" signal de-asserted, the output will be 0.
// The input is a vector of booleans, with each Bool representing
// a requestor. The output is a vector of booleans of the same
// length. Up to only 1 bit can be asserted (or all bits are 0)
// at the output. The integer input "highest priority" indicates
// which requestor (corresponding to the input vector) gets the
// highest priority.
// Note: from Eric
//---------------------------------------------------------------------
function Vector#(n, Bool) priority_encoder_onehot( Integer highest_priority, Bool en, Vector#(n, Bool) vec );
Bool selected = False;
Vector#(n, Bool) choice = unpack(0);
for(Integer i=highest_priority; i < valueOf(n); i=i+1) begin
if(vec[i] && !selected) begin
selected = True;
choice[i] = True;
end
end
// wrap around
for(Integer i=0; i < highest_priority; i=i+1) begin
if(vec[i] && !selected) begin
selected = True;
choice[i] = True;
end
end
if(!en) choice = unpack(0);
return choice;
endfunction
interface Arbiter#(type n);
(* always_ready *) method Vector#(n, Bool) select( Vector#(n, Bool) requests );
(* always_ready *) method Action next();
endinterface
module mkStaticPriorityArbiter(Arbiter#(n));
method Vector#(n, Bool) select( Vector#(n, Bool) requests );
return static_priority_arbiter_onehot(requests);
endmethod
method Action next();
action noAction; endaction
endmethod
endmodule
module mkStaticPriorityArbiterStartAt#(Integer startAt) (Arbiter#(n));
method Vector#(n, Bool) select( Vector#(n, Bool) requests );
return static_priority_arbiter_onehot_start_at(requests, startAt);
endmethod
method Action next();
action noAction; endaction
endmethod
endmodule
//module mkRoundRobinArbiter(Arbiter#(n));
// method ActionValue#(Vector#(n, Bool)) select( Vector#(n, Bool) requests );
// return priority_arbiter_onehot(requests);
// endmethod
//endmodule
// From Bill Dally, page 354 in Dally's book
(* noinline *)
function Tuple2#(Bool,Bool) gen_grant_carry(Bool c, Bool r, Bool p);
return tuple2(r && (c || p), !r && (c || p)); // grant and carry signals
endfunction
//////////////////////////////////////////////////////
// Round-robin arbiter from Dally's book. Page 354
module mkRoundRobinArbiter( Arbiter#(n) );
Reg#(Vector#(n, Bool)) token <- mkReg(unpack(1));
method Vector#(n, Bool) select( Vector#(n, Bool) requests );
Vector#(n, Bool) granted_A = unpack(0);
Vector#(n, Bool) granted_B = unpack(0);
/////////////////////////////////////////////////////////////////////
// Replicated arbiters are used to avoid cyclical carry chain
// (see page 354, footnote 2 in Dally's book)
/////////////////////////////////////////////////////////////////////
// Arbiter 1
Bool carry = False;
for(Integer i=0; i < valueOf(n); i=i+1) begin
let gc = gen_grant_carry(carry, requests[i], token[i]);
granted_A[i] = tpl_1(gc);
carry = tpl_2(gc);
end
// Arbiter 2 (uses the carry from Arbiter 1)
for(Integer i=0; i < valueOf(n); i=i+1) begin
let gc = gen_grant_carry(carry, requests[i], token[i]);
granted_B[i] = tpl_1(gc);
carry = tpl_2(gc);
end
Vector#(n, Bool) winner = unpack(0);
//Maybe#(Bit#(m)) winner = Invalid;
for(Integer k=0; k < valueOf(n); k=k+1) begin
if(granted_A[k] || granted_B[k]) begin
winner = unpack(0);
winner[k] = True;
end
end
return winner;
endmethod
method Action next();
action
token <= rotate( token ); // WRONG -> this should get
endaction
endmethod
endmodule
//////////////////////////////////////////////////////
// Round-robin arbiter from Dally's book. Page 354
// Modified version to initialize with custom starting priority
module mkRoundRobinArbiterStartAt#(Integer startAt)( Arbiter#(n) );
Vector#(n, Bool) init_token = unpack(0);
init_token[startAt] = True;
Reg#(Vector#(n, Bool)) token <- mkReg(init_token);
method Vector#(n, Bool) select( Vector#(n, Bool) requests );
Vector#(n, Bool) granted_A = unpack(0);
Vector#(n, Bool) granted_B = unpack(0);
/////////////////////////////////////////////////////////////////////
// Replicated arbiters are used to avoid cyclical carry chain
// (see page 354, footnote 2 in Dally's book)
/////////////////////////////////////////////////////////////////////
// Arbiter 1
Bool carry = False;
for(Integer i=0; i < valueOf(n); i=i+1) begin
let gc = gen_grant_carry(carry, requests[i], token[i]);
granted_A[i] = tpl_1(gc);
carry = tpl_2(gc);
end
// Arbiter 2 (uses the carry from Arbiter 1)
for(Integer i=0; i < valueOf(n); i=i+1) begin
let gc = gen_grant_carry(carry, requests[i], token[i]);
granted_B[i] = tpl_1(gc);
carry = tpl_2(gc);
end
Vector#(n, Bool) winner = unpack(0);
//Maybe#(Bit#(m)) winner = Invalid;
for(Integer k=0; k < valueOf(n); k=k+1) begin
if(granted_A[k] || granted_B[k]) begin
winner = unpack(0);
winner[k] = True;
end
end
return winner;
endmethod
method Action next();
action
token <= rotate( token ); // WRONG -> this should get
endaction
endmethod
endmodule
module mkIterativeArbiter_fromEric( Arbiter#(n) );
Reg#(Vector#(n, Bool)) token <- mkReg(unpack(1));
method Vector#(n, Bool) select( Vector#(n, Bool) requests );
Vector#(n, Bool) granted = unpack(0);
for(Integer i=0; i < valueOf(n); i=i+1) begin
let outcome = priority_encoder_onehot( i, token[i], requests );
for(Integer j=0; j < valueOf(n); j=j+1) begin
granted[j] = granted[j] || outcome[j];
end
end
Vector#(n, Bool) winner = unpack(0);
//Maybe#(Bit#(m)) winner = Invalid;
for(Integer k=0; k < valueOf(n); k=k+1) begin
if(granted[k]) begin
winner = unpack(0);
winner[k] = True;
end
end
return winner;
endmethod
method Action next();
action
token <= rotate( token );
endaction
endmethod
endmodule
module mkIterativeArbiter_fromEricStartAt#(Integer startAt) ( Arbiter#(n) );
//Reg#(Vector#(n, Bool)) token <- mkReg(unpack(1));
Vector#(n, Bool) init_token = unpack(0);
init_token[startAt] = True;
Reg#(Vector#(n, Bool)) token <- mkReg(init_token);
method Vector#(n, Bool) select( Vector#(n, Bool) requests );
Vector#(n, Bool) granted = unpack(0);
for(Integer i=0; i < valueOf(n); i=i+1) begin
let outcome = priority_encoder_onehot( i, token[i], requests );
for(Integer j=0; j < valueOf(n); j=j+1) begin
granted[j] = granted[j] || outcome[j];
end
end
Vector#(n, Bool) winner = unpack(0);
//Maybe#(Bit#(m)) winner = Invalid;
for(Integer k=0; k < valueOf(n); k=k+1) begin
if(granted[k]) begin
winner = unpack(0);
winner[k] = True;
end
end
return winner;
endmethod
method Action next();
action
token <= rotate( token );
endaction
endmethod
endmodule
//------ Testing ----------
(* synthesize *)
module mkTestArbiter8(Arbiter#(8));
//Arbiter#(8) arb <- mkStaticPriorityArbiter();
Arbiter#(8) arb <- mkStaticPriorityArbiterStartAt(2);
//Arbiter#(8) arb <- mkRoundRobinArbiter();
//Arbiter#(8) arb <- mkRoundRobinArbiterStartAt(2);
//Arbiter#(8) arb <- mkIterativeArbiter_fromEric();
return arb;
//method select = arb.select;
//method next = arb.next;
endmodule