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write_verilog: correctly emit asynchronous transparent ports.

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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.
This commit is contained in:
whitequark 2019-01-29 02:24:00 +00:00
parent 266511b29e
commit da65e1e8d9
1 changed files with 41 additions and 38 deletions
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79
backends/verilog/verilog_backend.cc
View file

@ -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(); 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_clk_posedge = cell->parameters["\\RD_CLK_POLARITY"].extract(i).as_bool();
rd_transparent = cell->parameters["\\RD_TRANSPARENT"].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; 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()) );
{ {
os << stringf("if ("); std::ostringstream os;
dump_sigspec(os, sig_rd_en); if (sig_rd_en != RTLIL::SigBit(true))
os << stringf(") "); {
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());
}
{
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: // for rd-transparent read-ports make something like:
// reg [..] temp_id; // reg [..] temp_id;
// always @(posedge clk) // 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()); 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); 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);
} }
} }