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splitnets: add -ports_only and -top_only options

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Add two new options to the splitnets pass:

- `-ports_only`: Split only module ports, not internal signals. This is
  useful when you want to split ports for interface compatibility while
  keeping internal signals as multi-bit wires for better readability.

- `-top_only`: Apply splitting only at the top module level, not in
  submodules. This is helpful for hierarchical designs where you need
  split signals only at the top-level interface.

These options can be combined with existing flags:
- `splitnets -ports_only`: Split all ports in all modules
- `splitnets -ports_only -top_only`: Split ports only in top module
- `splitnets -ports -top_only`: Split both ports and nets only in top

Add comprehensive tests that verify wire/port counts for all flag
combinations using a hierarchical design.
This commit is contained in:
Natalia 2026-01-14 01:43:55 -08:00
parent 71feb2a2a1
commit 6503ad91c9
4 changed files with 107 additions and 12 deletions
Download patch file Download diff file Expand all files Collapse all files

42
passes/cmds/splitnets.cc
View file

@ -113,6 +113,12 @@ struct SplitnetsPass : public Pass {
log(" -ports\n");
log(" also split module ports. per default only internal signals are split.\n");
log("\n");
log(" -ports_only\n");
log(" split module ports, but not the internal signals.\n");
log("\n");
log(" -top_only\n");
log(" split module ports/nets, only at the top level of hierarchy.\n");
log("\n");
log(" -driver\n");
log(" don't blindly split nets in individual bits. instead look at the driver\n");
log(" and split nets so that no driver drives only part of a net.\n");
@ -122,6 +128,8 @@ struct SplitnetsPass : public Pass {
{
bool flag_ports = false;
bool flag_driver = false;
bool flag_ports_only = false;
bool flag_top_only = false;
std::string format = "[]:";
log_header(design, "Executing SPLITNETS pass (splitting up multi-bit signals).\n");
@ -137,6 +145,14 @@ struct SplitnetsPass : public Pass {
flag_ports = true;
continue;
}
if (args[argidx] == "-ports_only") {
flag_ports_only = true;
continue;
}
if (args[argidx] == "-top_only") {
flag_top_only = true;
continue;
}
if (args[argidx] == "-driver") {
flag_driver = true;
continue;
@ -152,11 +168,12 @@ struct SplitnetsPass : public Pass {
{
if (module->has_processes_warn())
continue;
if (flag_top_only && (design->top_module() != module)) {
continue;
}
SplitnetsWorker worker;
if (flag_ports)
{
if (flag_ports || flag_ports_only) {
int normalized_port_factor = 0;
for (auto wire : module->wires())
@ -187,7 +204,8 @@ struct SplitnetsPass : public Pass {
for (auto &chunk : sig.chunks()) {
if (chunk.wire == NULL)
continue;
if (chunk.wire->port_id == 0 || flag_ports) {
if ((flag_ports_only && (chunk.wire->port_id != 0)) ||
(!flag_ports_only && (chunk.wire->port_id == 0 || flag_ports))) {
if (chunk.offset != 0)
split_wires_at[chunk.wire].insert(chunk.offset);
if (chunk.offset + chunk.width < chunk.wire->width)
@ -204,11 +222,12 @@ struct SplitnetsPass : public Pass {
}
worker.append_wire(module, it.first, cursor, it.first->width - cursor, format);
}
}
else
{
} else {
for (auto wire : module->wires()) {
if (((wire->width > 1) || (wire->has_attribute(ID::single_bit_vector)))
if (flag_ports_only) {
if (wire->width > 1 && (wire->port_id != 0) && design->selected(module, wire))
worker.splitmap[wire] = std::vector<RTLIL::SigBit>();
} else if (((wire->width > 1) || (wire->has_attribute(ID::single_bit_vector)))
&& (wire->port_id == 0 || flag_ports)
&& design->selected(module, wire)) {
wire->attributes.erase(ID::single_bit_vector);
@ -223,9 +242,8 @@ struct SplitnetsPass : public Pass {
module->rewrite_sigspecs(worker);
if (flag_ports)
{
for (auto wire : module->wires())
if (flag_ports || flag_ports_only) {
for (auto wire : module->wires())
{
if (wire->port_id == 0)
continue;
@ -248,7 +266,7 @@ struct SplitnetsPass : public Pass {
delete_wires.insert(it.first);
module->remove(delete_wires);
if (flag_ports)
if (flag_ports || flag_ports_only)
module->fixup_ports();
}

63
tests/various/test_splitnets.tcl Normal file
View file

@ -0,0 +1,63 @@
yosys -import
proc read_stats { file } {
set fid [open $file]
set result [read $fid]
close $fid
set ports 0
set nets 0
foreach line [split $result "\n"] {
if [regexp {Number of wires:[ \t]+([0-9]+)} $line tmp n] {
set nets [expr $nets + $n]
}
if [regexp {Number of ports:[ \t]+([0-9]+)} $line tmp n] {
set ports [expr $ports + $n]
}
}
return [list $nets $ports]
}
proc assert_count { type actual expected } {
if {$actual != $expected} {
puts "Error, $type count: $actual vs $expected expected"
exit 1
}
}
read_verilog test_splitnets.v
hierarchy -auto-top
procs
design -save "pre"
splitnets -ports_only -top_only
write_verilog -noexpr "ports_only_in_top.v"
tee -o "ports_only_in_top.txt" stat
foreach {nets ports} [read_stats "ports_only_in_top.txt"] {}
assert_count "nets" $nets 26
assert_count "ports" $ports 16
design -load "pre"
splitnets -ports_only
write_verilog -noexpr "ports_only_in_all.v"
tee -o "ports_only_in_all.txt" stat
foreach {nets ports} [read_stats "ports_only_in_all.txt"] {}
assert_count "nets" $nets 30
assert_count "ports" $ports 20
design -load "pre"
splitnets -ports -top_only
write_verilog -noexpr "ports_nets_in_top.v"
tee -o "ports_nets_in_top.txt" stat
foreach {nets ports} [read_stats "ports_nets_in_top.txt"] {}
assert_count "nets" $nets 30
assert_count "ports" $ports 16
design -load "pre"
splitnets -ports
write_verilog -noexpr "ports_nets_in_all.v"
tee -o "ports_nets_in_all.txt" stat
foreach {nets ports} [read_stats "ports_nets_in_all.txt"] {}
assert_count "nets" $nets 40
assert_count "ports" $ports 20
exit 0

13
tests/various/test_splitnets.v Normal file
View file

@ -0,0 +1,13 @@
module bottom(input clk, input wire [1:0] i, output reg [1:0] q);
reg [1:0] q1;
always @(posedge clk) begin
q1 <= i;
q <= q1;
end
endmodule
module top(input clk, input wire [1:0] i, output wire [1:0] q);
wire [1:0] q1;
bottom u1 (.clk(clk), .i(i), .q(q1));
assign q = ~q1;
endmodule

1
tests/various/test_splitnets.ys Normal file
View file

@ -0,0 +1 @@
tcl test_splitnets.tcl