caiyu/nextpnr
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

ice40: Creating a carry chain splitter function

Browse Source 
Signed-off-by: David Shah <davey1576@gmail.com>
This commit is contained in:
David Shah 2018-06-25 15:39:46 +02:00
parent 8d9444b6f0
commit 6d154cfa13
3 changed files with 77 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
common/nextpnr.h
View File

@ -207,13 +207,13 @@ struct BaseCtx
IdString::initialize_add(this, "", 0);
IdString::initialize_arch(this);
}
~BaseCtx()
{
for(auto &item : nets) {
for (auto &item : nets) {
delete item.second;
}
for(auto &item : cells) {
for (auto &item : cells) {
delete item.second;
}
delete idstring_str_to_idx;

12
ice40/pack.cc
View File

@ -258,7 +258,7 @@ static void pack_constants(Context *ctx)
std::vector<IdString> dead_nets;
bool gnd_used = false, vcc_used = false;
bool gnd_used = false;
for (auto net : sorted(ctx->nets)) {
NetInfo *ni = net.second;
@ -268,7 +268,6 @@ static void pack_constants(Context *ctx)
dead_nets.push_back(net.first);
} else if (ni->driver.cell != nullptr && ni->driver.cell->type == ctx->id("VCC")) {
set_net_constant(ctx, ni, vcc_net, true);
vcc_used = true;
dead_nets.push_back(net.first);
}
}
@ -277,11 +276,10 @@ static void pack_constants(Context *ctx)
ctx->cells[gnd_cell->name] = gnd_cell;
ctx->nets[gnd_net->name] = gnd_net;
}
if (vcc_used) {
ctx->cells[vcc_cell->name] = vcc_cell;
ctx->nets[vcc_net->name] = vcc_net;
}
// Vcc cell always inserted for now, as it may be needed during carry legalisation (TODO: trim later if actually
// never used?)
ctx->cells[vcc_cell->name] = vcc_cell;
ctx->nets[vcc_net->name] = vcc_net;
for (auto dn : dead_nets)
ctx->nets.erase(dn);

78
ice40/place_legaliser.cc
View File

@ -27,13 +27,18 @@
NEXTPNR_NAMESPACE_BEGIN
struct CellChain
{
std::vector<CellInfo *> cells;
};
// Generic chain finder
template <typename F1, typename F2, typename F3>
std::vector<std::vector<CellInfo *>> find_chains(const Context *ctx, F1 cell_type_predicate, F2 get_previous,
F3 get_next, size_t min_length = 2)
std::vector<CellChain> find_chains(const Context *ctx, F1 cell_type_predicate, F2 get_previous, F3 get_next,
size_t min_length = 2)
{
std::set<IdString> chained;
std::vector<std::vector<CellInfo *>> chains;
std::vector<CellChain> chains;
for (auto cell : sorted(ctx->cells)) {
if (chained.find(cell.first) != chained.end())
continue;
@ -45,15 +50,15 @@ std::vector<std::vector<CellInfo *>> find_chains(const Context *ctx, F1 cell_typ
start = prev_start;
prev_start = get_previous(ctx, start);
}
std::vector<CellInfo *> chain;
CellChain chain;
CellInfo *end = start;
while (end != nullptr) {
chain.push_back(end);
chain.cells.push_back(end);
end = get_next(ctx, end);
}
if (chain.size() >= min_length) {
if (chain.cells.size() >= min_length) {
chains.push_back(chain);
for (auto c : chain)
for (auto c : chain.cells)
chained.insert(c->name);
}
}
@ -95,7 +100,7 @@ class PlacementLegaliser
private:
bool legalise_carries()
{
std::vector<std::vector<CellInfo *>> carry_chains = find_chains(
std::vector<CellChain> carry_chains = find_chains(
ctx, is_lc,
[](const Context *ctx, const CellInfo *cell) {
return net_driven_by(ctx, cell->ports.at(ctx->id("CIN")).net, is_lc, ctx->id("COUT"));
@ -103,15 +108,63 @@ class PlacementLegaliser
[](const Context *ctx, const CellInfo *cell) {
return net_only_drives(ctx, cell->ports.at(ctx->id("COUT")).net, is_lc, ctx->id("CIN"), false);
});
// TODO
for (auto chain : carry_chains) {
}
return true;
}
// Split a carry chain into multiple legal chains
std::vector<CellChain> split_carry_chain(Context *ctx, CellChain &carryc)
{
bool start_of_chain = true;
std::vector<CellChain> chains;
std::vector<const CellInfo *> tile;
const int max_length = (ctx->chip_info->height - 2) * 8 - 2;
auto curr_cell = carryc.cells.begin();
while (curr_cell != carryc.cells.end()) {
CellInfo *cell = *curr_cell;
if (tile.size() >= 8) {
tile.clear();
}
if (start_of_chain) {
tile.clear();
chains.emplace_back();
start_of_chain = false;
if (cell->ports.at(ctx->id("CIN")).net) {
// CIN is not constant and not part of a chain. Must feed in from fabric
CellInfo *feedin = make_carry_feed_in(cell, cell->ports.at(ctx->id("CIN")));
chains.back().cells.push_back(feedin);
tile.push_back(feedin);
}
}
tile.push_back(cell);
chains.back().cells.push_back(cell);
bool split_chain = (!ctx->logicCellsCompatible(tile)) || (int(chains.back().cells.size()) > max_length);
if (split_chain) {
CellInfo *passout = make_carry_pass_out(cell->ports.at(ctx->id("COUT")));
tile.pop_back();
chains.back().cells.back() = passout;
start_of_chain = true;
} else {
NetInfo *carry_net = cell->ports.at(ctx->id("COUT")).net;
if (carry_net != nullptr && carry_net->users.size() > 1) {
CellInfo *passout = make_carry_pass_out(cell->ports.at(ctx->id("COUT")));
chains.back().cells.push_back(passout);
tile.push_back(passout);
}
++curr_cell;
}
}
return chains;
}
// Insert a logic cell to legalise a COUT->fabric connection
CellInfo *make_carry_pass_out(PortInfo &cout_port)
{
assert(cout_port.net != nullptr);
CellInfo *lc = create_ice_cell(ctx, ctx->id("ICESTORM_LC"));
lc->params[ctx->id("LUT_INIT")] = "65280"; // 0xff00: O = I3
lc->params[ctx->id("CARRY_ENABLE")] = "1";
lc->ports.at(ctx->id("O")).net = cout_port.net;
NetInfo *co_i3_net = new NetInfo();
co_i3_net->name = ctx->id(lc->name.str(ctx) + "$I3");
@ -125,11 +178,18 @@ class PlacementLegaliser
o_r.cell = lc;
cout_port.net->driver = o_r;
lc->ports.at(ctx->id("I3")).net = co_i3_net;
// I1=1 feeds carry up the chain, so no need to actually break the chain
lc->ports.at(ctx->id("I1")).net = ctx->nets.at(ctx->id("$PACKER_VCC_NET"));
PortRef i1_r;
i1_r.port = ctx->id("I1");
i1_r.cell = lc;
ctx->nets.at(ctx->id("$PACKER_VCC_NET"))->users.push_back(i1_r);
ctx->cells[lc->name] = lc;
createdCells.insert(lc->name);
return lc;
}
// Insert a logic cell to legalise a CIN->fabric connection
CellInfo *make_carry_feed_in(CellInfo *cin_cell, PortInfo &cin_port)
{
assert(cin_port.net != nullptr);