From da65e1e8d9552f64e1e03c08108ca0532719bbfe Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Tue, 29 Jan 2019 02:24:00 +0000
Subject: write_verilog: correctly emit asynchronous transparent ports.
This commit fixes two related issues:
* For asynchronous ports, clock is no longer added to domain list.
(This would lead to absurd constructs like `always @(posedge 0)`.
* The logic to distinguish synchronous and asynchronous ports is
changed to correctly use or avoid clock in all cases.
Before this commit, the following RTLIL snippet (after memory_collect)
cell $memrd $2
parameter \MEMID "\\mem"
parameter \ABITS 2
parameter \WIDTH 4
parameter \CLK_ENABLE 0
parameter \CLK_POLARITY 1
parameter \TRANSPARENT 1
connect \CLK 1'0
connect \EN 1'1
connect \ADDR \mem_r_addr
connect \DATA \mem_r_data
end
would lead to invalid Verilog:
reg [1:0] _0_;
always @(posedge 1'h0) begin
_0_ <= mem_r_addr;
end
assign mem_r_data = mem[_0_];
Note that there are two potential pitfalls remaining after this
change:
* For asynchronous ports, the \EN input and \TRANSPARENT parameter
are silently ignored. (Per discussion in #760 this is the correct
behavior.)
* For synchronous transparent ports, the \EN input is ignored. This
matches the behavior of the $mem simulation cell. Again, see #760.
---
backends/verilog/verilog_backend.cc | 79 +++++++++++++++++++------------------
1 file changed, 41 insertions(+), 38 deletions(-)
diff --git a/backends/verilog/verilog_backend.cc b/backends/verilog/verilog_backend.cc
index a7f329ef8..60668f1f0 100644
--- a/backends/verilog/verilog_backend.cc
+++ b/backends/verilog/verilog_backend.cc
@@ -1065,43 +1065,46 @@ bool dump_cell_expr(std::ostream &f, std::string indent, RTLIL::Cell *cell)
use_rd_clk = cell->parameters["\\RD_CLK_ENABLE"].extract(i).as_bool();
rd_clk_posedge = cell->parameters["\\RD_CLK_POLARITY"].extract(i).as_bool();
rd_transparent = cell->parameters["\\RD_TRANSPARENT"].extract(i).as_bool();
+ if (use_rd_clk)
{
- std::ostringstream os;
- dump_sigspec(os, sig_rd_clk);
- clk_domain_str = stringf("%sedge %s", rd_clk_posedge ? "pos" : "neg", os.str().c_str());
- if( clk_to_lof_body.count(clk_domain_str) == 0 )
- clk_to_lof_body[clk_domain_str] = std::vector<std::string>();
- }
- if (use_rd_clk && !rd_transparent)
- {
- // for clocked read ports make something like:
- // reg [..] temp_id;
- // always @(posedge clk)
- // if (rd_en) temp_id <= array_reg[r_addr];
- // assign r_data = temp_id;
- std::string temp_id = next_auto_id();
- lof_reg_declarations.push_back( stringf("reg [%d:0] %s;\n", sig_rd_data.size() - 1, temp_id.c_str()) );
{
std::ostringstream os;
- if (sig_rd_en != RTLIL::SigBit(true))
+ dump_sigspec(os, sig_rd_clk);
+ clk_domain_str = stringf("%sedge %s", rd_clk_posedge ? "pos" : "neg", os.str().c_str());
+ if( clk_to_lof_body.count(clk_domain_str) == 0 )
+ clk_to_lof_body[clk_domain_str] = std::vector<std::string>();
+ }
+ if (!rd_transparent)
+ {
+ // for clocked read ports make something like:
+ // reg [..] temp_id;
+ // always @(posedge clk)
+ // if (rd_en) temp_id <= array_reg[r_addr];
+ // assign r_data = temp_id;
+ std::string temp_id = next_auto_id();
+ lof_reg_declarations.push_back( stringf("reg [%d:0] %s;\n", sig_rd_data.size() - 1, temp_id.c_str()) );
+ {
+ std::ostringstream os;
+ if (sig_rd_en != RTLIL::SigBit(true))
+ {
+ os << stringf("if (");
+ dump_sigspec(os, sig_rd_en);
+ os << stringf(") ");
+ }
+ os << stringf("%s <= %s[", temp_id.c_str(), mem_id.c_str());
+ dump_sigspec(os, sig_rd_addr);
+ os << stringf("];\n");
+ clk_to_lof_body[clk_domain_str].push_back(os.str());
+ }
{
- os << stringf("if (");
- dump_sigspec(os, sig_rd_en);
- os << stringf(") ");
+ std::ostringstream os;
+ dump_sigspec(os, sig_rd_data);
+ std::string line = stringf("assign %s = %s;\n", os.str().c_str(), temp_id.c_str());
+ clk_to_lof_body[""].push_back(line);
}
- os << stringf("%s <= %s[", temp_id.c_str(), mem_id.c_str());
- dump_sigspec(os, sig_rd_addr);
- os << stringf("];\n");
- clk_to_lof_body[clk_domain_str].push_back(os.str());
}
+ else
{
- std::ostringstream os;
- dump_sigspec(os, sig_rd_data);
- std::string line = stringf("assign %s = %s;\n", os.str().c_str(), temp_id.c_str());
- clk_to_lof_body[""].push_back(line);
- }
- } else {
- if (rd_transparent) {
// for rd-transparent read-ports make something like:
// reg [..] temp_id;
// always @(posedge clk)
@@ -1121,15 +1124,15 @@ bool dump_cell_expr(std::ostream &f, std::string indent, RTLIL::Cell *cell)
std::string line = stringf("assign %s = %s[%s];\n", os.str().c_str(), mem_id.c_str(), temp_id.c_str());
clk_to_lof_body[""].push_back(line);
}
- } else {
- // for non-clocked read-ports make something like:
- // assign r_data = array_reg[r_addr];
- std::ostringstream os, os2;
- dump_sigspec(os, sig_rd_data);
- dump_sigspec(os2, sig_rd_addr);
- std::string line = stringf("assign %s = %s[%s];\n", os.str().c_str(), mem_id.c_str(), os2.str().c_str());
- clk_to_lof_body[""].push_back(line);
}
+ } else {
+ // for non-clocked read-ports make something like:
+ // assign r_data = array_reg[r_addr];
+ std::ostringstream os, os2;
+ dump_sigspec(os, sig_rd_data);
+ dump_sigspec(os2, sig_rd_addr);
+ std::string line = stringf("assign %s = %s[%s];\n", os.str().c_str(), mem_id.c_str(), os2.str().c_str());
+ clk_to_lof_body[""].push_back(line);
}
}
--
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