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ice40: Working on carry legalisation

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Signed-off-by: David Shah <davey1576@gmail.com>
This commit is contained in:
David Shah 2018-06-26 12:01:11 +02:00
parent ac197e0b9e
commit 0a176b4fde
1 changed files with 75 additions and 11 deletions
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86
ice40/place_legaliser.cc
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@ -30,6 +30,7 @@ NEXTPNR_NAMESPACE_BEGIN
struct CellChain
{
std::vector<CellInfo *> cells;
float mid_x = 0, mid_y = 0;
};
// Generic chain finder
@ -92,6 +93,7 @@ class PlacementLegaliser
bool legalise()
{
init_logic_cells();
bool legalised_carries = legalise_carries();
if (!legalised_carries && !ctx->force)
return false;
@ -113,9 +115,9 @@ class PlacementLegaliser
int x = bi.x, y = bi.y, z = bi.z;
IdString cell = ctx->getBoundBelCell(bel);
if (cell != IdString() && ctx->cells.at(cell)->belStrength >= STRENGTH_FIXED)
logic_bels.at(x).at(y).at(z) = std::make_pair(bel, true);
logic_bels.at(x).at(y).at(z) = std::make_pair(bel, true); // locked out of use
else
logic_bels.at(x).at(y).at(z) = std::make_pair(bel, false);
logic_bels.at(x).at(y).at(z) = std::make_pair(bel, false); // available
}
}
}
@ -130,24 +132,69 @@ 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);
});
int width = ctx->chip_info->width, height = ctx->chip_info->height;
bool success = true;
// Find midpoints for all chains, before we start tearing them up
std::vector<CellChain> all_chains;
for (auto &base_chain : carry_chains) {
std::vector<CellChain> split_chains = split_carry_chain(base_chain);
for (auto &chain : split_chains) {
float mid_x, mid_y;
get_chain_midpoint(ctx, chain, mid_x, mid_y);
float base_x = mid_x, base_y = mid_y - (chain.cells.size() / 16.0f);
// Find Bel meeting requirements closest to the target base
get_chain_midpoint(ctx, chain, chain.mid_x, chain.mid_y);
all_chains.push_back(chain);
}
}
return true;
// Actual chain placement
for (auto &chain : all_chains) {
float base_x = chain.mid_x, base_y = chain.mid_y - (chain.cells.size() / 16.0f);
// Find Bel meeting requirements closest to the target base, returning location as <x, y, z>
auto chain_origin_bel = find_closest_bel(base_x, base_y, int(chain.cells.size()));
int place_x = std::get<0>(chain_origin_bel), place_y = std::get<1>(chain_origin_bel),
place_z = std::get<2>(chain_origin_bel);
if (place_x == -1) {
if (ctx->force) {
log_warning("failed to place carry chain, starting with cell '%s', length %d\n",
chain.cells.front()->name.c_str(ctx), int(chain.cells.size()));
success = false;
continue;
} else {
log_error("failed to place carry chain, starting with cell '%s', length %d\n",
chain.cells.front()->name.c_str(ctx), int(chain.cells.size()));
}
}
// Place carry chain
for (int i = 0; i < int(chain.cells.size()); i++) {
int target_z = place_y * 8 + place_z + i;
place_lc(chain.cells.at(i), place_x, target_z / 8, target_z % 8);
}
}
return success;
}
// Find Bel closest to a location, meeting chain requirements
BelId find_closest_bel(float x, float y, int chain_size)
std::tuple<int, int, int> find_closest_bel(float target_x, float target_y, int chain_size)
{
// TODO
return BelId();
std::tuple<int, int, int> best_origin = std::make_tuple(-1, -1, -1);
float smallest_distance = std::numeric_limits<float>::infinity();
int width = ctx->chip_info->width, height = ctx->chip_info->height;
// Slow, should radiate outwards from target position - TODO
for (int x = 1; x < width; x++) {
for (int y = 1; y < (height - (chain_size / 8)); y++) {
bool valid = true;
for (int k = 0; k < chain_size; k++) {
if (logic_bels.at(x).at(y + k / 8).at(k % 8).second) {
valid = false;
break;
}
}
if (valid) {
float distance = (x - target_x) * (x - target_x) + (y - target_y) * (y - target_y);
if (distance < smallest_distance) {
smallest_distance = distance;
best_origin = std::make_tuple(x, y, 0);
}
}
}
}
return best_origin;
}
// Split a carry chain into multiple legal chains
@ -195,6 +242,23 @@ class PlacementLegaliser
return chains;
}
// Place a logic cell at a given grid location, handling rip-up etc
void place_lc(CellInfo *cell, int x, int y, int z)
{
auto &loc = logic_bels.at(x).at(y).at(z);
assert(!loc.second);
BelId bel = loc.first;
// Check if there is a cell presently at the location, which we will need to rip up
IdString existing = ctx->getBoundBelCell(bel);
if (existing != IdString()) {
// TODO: keep track of the previous position of the ripped up cell, as a hint
rippedCells.insert(existing);
ctx->unbindBel(bel);
}
ctx->bindBel(bel, cell->name, STRENGTH_LOCKED);
loc.second = true; // Bel is now unavailable for further use
}
// Insert a logic cell to legalise a COUT->fabric connection
CellInfo *make_carry_pass_out(PortInfo &cout_port)
{