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Fix issue #40

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This commit is contained in:
Florian Zaruba 2017-06-02 11:42:42 +02:00
parent 72b842eaf8
commit 473aee92ab
2 changed files with 42 additions and 15 deletions
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55
src/if_stage.sv
View file

@ -57,7 +57,7 @@ module if_stage (
//---------------------------------
// we are busy if we are either waiting for a grant
// or if the FIFO is full
assign if_busy_o = ((CS == WAIT_GNT || CS == WAIT_ABORTED) && !instr_req_o) || !fifo_ready;
assign if_busy_o = ((CS == WAIT_GNT) && !instr_req_o) || !fifo_ready;
assign fetch_address = {fetch_address_i[63:2], 2'b0};
//---------------------------------
@ -105,7 +105,9 @@ module if_stage (
else
NS = WAIT_RVALID;
else begin //~> got a request but no grant
NS = WAIT_GNT;
// if we flush we want to stay in the IDLE state
if (!flush_i)
NS = WAIT_GNT;
end
end
end // case: IDLE
@ -115,14 +117,19 @@ module if_stage (
instr_addr_o = {instr_addr_q[63:2], 2'b0};
instr_req_o = 1'b1;
if(instr_gnt_i)
if(instr_gnt_i) begin
// we have one outstanding rvalid: wait for it
if (flush_i)
NS = WAIT_ABORTED;
else
NS = WAIT_RVALID;
else
NS = WAIT_GNT;
end else begin
// if we got a flush request we can safely return to IDLE
if (flush_i)
NS = IDLE;
else
NS = WAIT_GNT;
end
end // case: WAIT_GNT
// we wait for rvalid, after that we are ready to serve a new request
@ -144,7 +151,10 @@ module if_stage (
else
NS = WAIT_RVALID;
end else begin
NS = WAIT_GNT;
if (!flush_i)
NS = WAIT_GNT; // lets wait for the grant
else // we didn't get a grant yet so go back to IDLE
NS = IDLE;
end
end
end else begin
@ -156,20 +166,27 @@ module if_stage (
// just wait for rvalid and go back to IDLE, no new request
if (instr_rvalid_i) begin
// if we are receiving a data item during a flush ignore it
fifo_valid = 1'b1;
NS = IDLE;
if (flush_i)
fifo_valid = 1'b0;
else
fifo_valid = 1'b1;
// in any case we can go back to IDLE safely
NS = IDLE;
end
end
end // case: WAIT_RVALID
// our last request was aborted, but we didn't yet get a rvalid and
// there was no new request sent yet we assume that req_i is set to high
// our last request was aborted, but we didn't yet get a rvalid
WAIT_ABORTED: begin
instr_addr_o = {fetch_address_i[63:2], 2'b0};
if (instr_rvalid_i) begin
// we are aborting this instruction so don't tell the FIFO it is valid
fifo_valid = 1'b0;
// we can do a new request here, we won't get a grant until the rvalid came back for the
// request we sent to end in here
instr_addr_o = fetch_address;
// we are aborting this instruction so don't tell the FIFO it is valid
fifo_valid = 1'b0;
// check if the fetch is valid before making a new request
if (fetch_valid_i) begin
instr_req_o = 1'b1;
if (instr_gnt_i) begin
@ -179,8 +196,16 @@ module if_stage (
else
NS = WAIT_RVALID;
end else begin
NS = WAIT_GNT;
// only if we are not flushing again leave the state
if (!flush_i)
NS = WAIT_GNT;
end
end else begin
if (instr_rvalid_i) begin
// we didn't make a new request but got the rvalid we where waiting for, go back to IDLE
NS = IDLE;
end
// otherwise wait in this state for the rvalid
end
end

2
src/pcgen.sv
View file

@ -82,6 +82,8 @@ module pcgen (
npc_n = {npc_q[62:2], 2'b0} + 64'h4;
else // or keep the PC stable if IF is not ready
npc_n = npc_q;
// we only need to stall the consecutive case since in any other case we will flush at least
// the front-end which means that the IF stage will always be ready to accept a new request
// -------------------------------
// 1. Predict taken