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Rewrite of non verific underfill/overfill

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w_underfill should provide identical results regardless of whether
or not Verific is used.  w_overfill doesn't have the extra check
for prettiness without Verific because I'm too lazy to do it.

Replaced $past function with past_nwen register to ensure correct
operation.

Expanded w_underfill under Verific to use a property block to more
easily compare the two versions side by side.

Changed Concurrent assertions section of doc to compare the two
implementations of w_underfill.  Should provide a better example
for why using verific makes it easier.
This commit is contained in:
KrystalDelusion 2022-08-09 11:33:29 +12:00
parent 1d4716a5f9
commit d6d7119cd5
3 changed files with 118 additions and 37 deletions
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50
docs/examples/fifo/fifo.sv
View file

@ -149,19 +149,45 @@ module fifo
ap_raddr3: assert property (@(posedge clk) disable iff (rst) !ren && !full |=> $stable(raddr));
ap_waddr3: assert property (@(posedge clk) disable iff (rst) !wen && !empty |=> $stable(waddr));
// can we corrupt our data?
w_underfill: cover property (@(posedge clk) disable iff (rst) !wen |=> $changed(waddr));
// look for an overfill where the value in memory changes
let d_change = (wdata != rdata);
w_overfill: cover property (@(posedge clk) disable iff (rst) !ren && d_change |=> $changed(raddr));
`else // !VERIFIC
always @(posedge clk) begin
if (~rst) begin
// this is less reliable because $past() can sometimes give false
// positives in the first cycle
w_overfill: cover ($past(rskip) && raddr);
w_underfill: cover ($past(wskip) && waddr);
// use block formatting for w_underfill so it's easier to describe in docs
// and is more readily comparable with the non SVA implementation
property write_skip;
@(posedge clk) disable iff (rst)
!wen |=> $changed(waddr);
endproperty
w_underfill: cover property (write_skip);
// look for an overfill where the value in memory changes
// the change in data makes certain that the value is overriden
let d_change = (wdata != rdata);
property read_skip;
@(posedge clk) disable iff (rst)
!ren && d_change |=> $changed(raddr);
endproperty
w_overfill: cover property (read_skip);
`else // !VERIFIC
// implementing w_underfill without properties
// can't use !$past(wen) since it will always trigger in the first cycle
reg past_nwen;
initial past_nwen <= 0;
always @(posedge clk) begin
if (rst) past_nwen <= 0;
if (!rst) begin
w_underfill: cover (past_nwen && $changed(waddr));
past_nwen <= !wen;
end
end
// end w_underfill
// w_overfill does the same, but has been separated so that w_underfill
// can be included in the docs more cleanly
reg past_nren;
initial past_nren <= 0;
always @(posedge clk) begin
if (rst) past_nren <= 0;
if (!rst) begin
w_overfill: cover (past_nren && $changed(raddr));
past_nren <= !ren;
end
end
`endif // VERIFIC

49
docs/examples/fifo/golden/fifo.sv
View file

@ -151,19 +151,44 @@ module fifo
ap_raddr3: assert property (@(posedge clk) disable iff (rst) !ren && !full |=> $stable(raddr));
ap_waddr3: assert property (@(posedge clk) disable iff (rst) !wen && !empty |=> $stable(waddr));
// can we corrupt our data?
w_underfill: cover property (@(posedge clk) disable iff (rst) !wen |=> $changed(waddr));
// look for an overfill where the value in memory changes
let d_change = (wdata != rdata);
w_overfill: cover property (@(posedge clk) disable iff (rst) !ren && d_change |=> $changed(raddr));
`else // !VERIFIC
always @(posedge clk) begin
if (~rst) begin
// this is less reliable because $past() can sometimes give false
// positives in the first cycle
w_overfill: cover ($past(rskip) && raddr);
w_underfill: cover ($past(wskip) && waddr);
// use block formatting for w_underfill so it's easier to describe in docs
// and is more readily comparable with the non SVA implementation
property write_skip;
@(posedge clk) disable iff (rst)
!wen |=> $changed(waddr);
endproperty
w_underfill: cover property (write_skip);
// look for an overfill where the value in memory changes
// the change in data makes certain that the value is overriden
property read_skip;
@(posedge clk) disable iff (rst)
!ren && d_change |=> $changed(raddr);
endproperty
w_overfill: cover property (read_skip);
`else // !VERIFIC
// implementing w_underfill without properties
// can't use !$past(wen) since it will always trigger in the first cycle
reg past_nwen;
initial past_nwen <= 0;
always @(posedge clk) begin
if (rst) past_nwen <= 0;
if (!rst) begin
w_underfill: cover (past_nwen && $changed(waddr));
past_nwen <= !wen;
end
end
// end w_underfill
// w_overfill does the same, but has been separated so that w_underfill
// can be included in the docs more cleanly
reg past_nren;
initial past_nren <= 0;
always @(posedge clk) begin
if (rst) past_nren <= 0;
if (!rst) begin
w_overfill: cover (past_nren && $changed(raddr));
past_nren <= !ren;
end
end
`endif // VERIFIC