This brings the documented behavior for these cells in line with
$_DFFSR_* and $_DLATCHSR_*, which is that R has priority over S.
The models were already reflecting that behavior.
Also get rid of sim-synth mismatch in the models while we're at it.
This pass is a proper subset of opt_rmdff, which is called by opt, which
is called by every synth flow in the coarse part. Thus, it never
actually does anything and can be safely removed.
By operating at a layer of abstraction over the rather clumsy Intel primitives,
we can avoid special hacks like `dffinit -highlow` in favour of simple techmapping.
This also makes the primitives much easier to manipulate, and more descriptive
(no more cyclonev_lcell_comb to mean anything from a LUT2 to a LUT6).
According to the official simulation model, and also cross-checked
on real hardware, the data output of the SPRAM when chipselect is
low is kept stable. It doesn't go undefined.
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
In some cases where multiple output pins share identical combinatorial
logic, yosys would only generate one $sop cell and therefore one
MACROCELL_XOR cell to try to feed the multiple sinks. This is not valid,
so make the fixup pass duplicate cells when necessary. For example,
fixes the following code:
module top(input a, input b, input clk_, output reg o, output o2);
wire clk;
BUFG bufg0 (
.I(clk_),
.O(clk),
);
always @(posedge clk)
o = a ^ b;
assign o2 = a ^ b;
endmodule
The new pass will contain all of the logic for inserting "passthrough"
product term and XOR cells as appropriate for the architecture. For
example, this commit fixes connecting an input pin directly to another
output pin with no logic in between.
This commit tries to carefully follow the documented behavior of LSE
and Synplify. It will use `syn_ramstyle` attribute if there are any
write ports, and `syn_romstyle` attribute otherwise.
* LSE supports both `syn_ramstyle` and `syn_romstyle`.
* Synplify only supports `syn_ramstyle`, with same values as LSE.
* Synplify also supports `syn_rw_conflict_logic`, which is not
documented as supported for LSE.
Limitations of the Yosys implementation:
* LSE/Synplify support `syn_ramstyle="block_ram,no_rw_check"`
syntax to turn off insertion of transparency logic. There is
currently no way to support multiple valued attributes in
memory_bram. It is also not clear if that is a good idea, since
it can cause sim/synth mismatches.
* LSE/Synplify/1364.1 support block ROM inference from full case
statements. Yosys does not currently perform this transformation.
* LSE/Synplify propagate `syn_ramstyle`/`syn_romstyle` attributes
from the module to the inner memories. There is currently no way
to do this in Yosys (attrmvcp only works on cells and wires).
This commit tries to carefully follow the documented behavior of LSE
and Synplify. It will use `syn_ramstyle` attribute if there are any
write ports, and `syn_romstyle` attribute otherwise.
* LSE supports both `syn_ramstyle` and `syn_romstyle`.
* Synplify only supports `syn_ramstyle`, with same values as LSE.
* Synplify also supports `syn_rw_conflict_logic`, which is not
documented as supported for LSE.
Limitations of the Yosys implementation:
* LSE/Synplify appear to interpret attribute values insensitive
to case. There is currently no way to do this in Yosys (attrmap
can only change case of attribute names).
* LSE/Synplify support `syn_ramstyle="block_ram,no_rw_check"`
syntax to turn off insertion of transparency logic. There is
currently no way to support multiple valued attributes in
memory_bram. It is also not clear if that is a good idea, since
it can cause sim/synth mismatches.
* LSE/Synplify/1364.1 support block ROM inference from full case
statements. Yosys does not currently perform this transformation.
* LSE/Synplify propagate `syn_ramstyle`/`syn_romstyle` attributes
from the module to the inner memories. There is currently no way
to do this in Yosys (attrmvcp only works on cells and wires).