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fabulous: pack more FF types: reset before enable 

Signed-off-by: Leo Moser <leomoser99@gmail.com>
This commit is contained in:
Leo Moser 2026-02-24 10:26:54 +01:00
parent 33fdfd7c31
commit 20de8b72e8
1 changed files with 79 additions and 17 deletions
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96
generic/viaduct/fabulous/pack.cc
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@ -97,16 +97,44 @@ struct FabulousPacker
void prepare_ffs()
{
// The following LUTFF are supported:
// Enable before reset: LUTFF_[N][E][AS|AR|SS|SR]
// Reset before enable: LUTFF_[N][AS|AR|SS|SR][E]
// Note: A simple LUTFF will have SR and EN disconnected,
// ensure that the default value is SR=0 and EN=1.
// N ... clock inversion (NEG_CLK=1)
// E ... clock enable (EN port)
// AS ... async set (SET_NORESET=1, ASYNC_SR=1)
// AR ... async reset (SET_NORESET=0, ASYNC_SR=1)
// SS ... sync set (SET_NORESET=1, ASYNC_SR=0)
// SR ... sync reset (SET_NORESET=0, ASYNC_SR=0)
// The ports of FABULOUS_FF are:
// - CLK: clock
// - SR: set/reset
// - EN: enable
// The parameters of FABULOUS_FF are:
// - SET_NORESET: the value to load into the flip-flop when SR=1
// - ASYNC_SR: used to indicate asynchronous load
// - NEG_CLK: invert the clock
// Note: Both ASYNC_SR and NEG_CLK are currently unused by the default FABulous fabric.
for (auto &cell : ctx->cells) {
CellInfo *ci = cell.second.get();
const std::string &type_str = ci->type.str(ctx);
if (type_str.size() < 5 || type_str.substr(0, 5) != "LUTFF")
continue;
ci->type = id_FABULOUS_FF;
// parse config string and unify
size_t idx = 5;
if (idx < type_str.size() && type_str.at(idx) == '_')
++idx;
// clock inversion
if (idx < type_str.size() && type_str.at(idx) == 'N') {
ci->params[id_NEG_CLK] = 1;
@ -114,36 +142,70 @@ struct FabulousPacker
} else {
ci->params[id_NEG_CLK] = 0;
}
// clock enable
// clock enable (enable before reset)
if (idx < type_str.size() && type_str.at(idx) == 'E')
++idx;
if (ci->ports.count(id_E))
ci->renamePort(id_E, id_EN);
else
ci->addInput(id_EN); // autocreate emtpy enable port if enable missing or unused
// sr presence and type
std::string srt = type_str.substr(idx);
if (srt == "S") {
ci->params[id_SET_NORESET] = 1;
ci->params[id_ASYNC_SR] = 1;
} else if (srt == "R") {
ci->params[id_SET_NORESET] = 0;
ci->params[id_ASYNC_SR] = 1;
} else if (srt == "SS") {
// default settings
ci->params[id_SET_NORESET] = 0;
ci->params[id_ASYNC_SR] = 0;
// synchronous set
if (idx < type_str.size() - 1 && type_str.substr(idx, 2) == "SS") {
ci->params[id_SET_NORESET] = 1;
ci->params[id_ASYNC_SR] = 0;
} else if (srt == "SR" || srt == "") {
idx += 2;
}
// synchronous reset
if (idx < type_str.size() - 1 && type_str.substr(idx, 2) == "SR") {
ci->params[id_SET_NORESET] = 0;
ci->params[id_ASYNC_SR] = 0;
} else {
idx += 2;
}
// asynchronous set
if (idx < type_str.size() - 1 && type_str.substr(idx, 2) == "AS") {
ci->params[id_SET_NORESET] = 1;
ci->params[id_ASYNC_SR] = 1;
idx += 2;
}
// asynchronous reset
if (idx < type_str.size() - 1 && type_str.substr(idx, 2) == "AR") {
ci->params[id_SET_NORESET] = 0;
ci->params[id_ASYNC_SR] = 1;
idx += 2;
}
// clock enable (reset before enable)
if (idx < type_str.size() && type_str.at(idx) == 'E')
++idx;
// check that we are the end of the string
if (idx != type_str.size()) {
log_error("unhandled FF type %s of cell %s\n", type_str.c_str(), ci->name.c_str(ctx));
NPNR_ASSERT_FALSE("unhandled FF type");
}
// Rename S/R ports to SR
if (ci->ports.count(id_S))
ci->renamePort(id_S, id_SR);
else if (ci->ports.count(id_R))
ci->renamePort(id_R, id_SR);
// Rename E port to EN
if (ci->ports.count(id_E))
ci->renamePort(id_E, id_EN);
// autocreate empty set/reset port if enable missing or unused
if (!ci->ports.count(id_SR))
ci->addInput(id_SR); // autocreate emtpy enable port if enable missing or unused
ci->addInput(id_SR);
// autocreate empty enable port if enable missing or unused
if (!ci->ports.count(id_EN))
ci->addInput(id_EN);
}
}