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interchange: Allow pseudo-cells with no input pins

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These are used for the LUT-as-GND-driver pseudo-pips in the Nexus arch,
which will probably be required for UltraScale too.

Signed-off-by: gatecat <gatecat@ds0.me>
This commit is contained in:
gatecat 2021-04-13 09:49:04 +01:00
parent 5cd2a7f9c2
commit 06e54f08e6
1 changed files with 34 additions and 13 deletions
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47
fpga_interchange/pseudo_pip_model.cc
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@ -156,7 +156,6 @@ void PseudoPipData::init_tile_type(const Context *ctx, int32_t tile_type)
} }
NPNR_ASSERT(output_bel_pin == bel.output_bel_pin); NPNR_ASSERT(output_bel_pin == bel.output_bel_pin);
NPNR_ASSERT(input_bel_pin != -1);
bel.input_bel_pin = input_bel_pin; bel.input_bel_pin = input_bel_pin;
logic_bels_for_pip[LogicBelKey{tile_type, pip_idx, site}].push_back(bel); logic_bels_for_pip[LogicBelKey{tile_type, pip_idx, site}].push_back(bel);
@ -378,13 +377,22 @@ void PseudoPipModel::update_site(const Context *ctx, size_t site)
cell.type = IdString(ctx->wire_lut->cell); cell.type = IdString(ctx->wire_lut->cell);
NPNR_ASSERT(ctx->wire_lut->input_pins.size() == 1); NPNR_ASSERT(ctx->wire_lut->input_pins.size() == 1);
cell.lut_cell.pins.push_back(IdString(ctx->wire_lut->input_pins[0])); cell.lut_cell.pins.push_back(IdString(ctx->wire_lut->input_pins[0]));
cell.lut_cell.equation.resize(2);
cell.lut_cell.equation.set(0, false);
cell.lut_cell.equation.set(1, true);
// Map LUT input to input wire used by pseudo pip. if (bel.input_bel_pin == -1) {
IdString input_bel_pin(bel_data.ports[bel.input_bel_pin]); // FIXME: currently assume that LUT route-throughs with no input pins are GND drivers as this is all we need
cell.cell_bel_pins[IdString(ctx->wire_lut->input_pins[0])].push_back(input_bel_pin); // for Nexus/Xilinx where Vcc is readily available and cheap This won't be true for other arches
cell.lut_cell.equation.resize(2);
cell.lut_cell.equation.set(0, false);
cell.lut_cell.equation.set(1, false);
} else {
cell.lut_cell.equation.resize(2);
cell.lut_cell.equation.set(0, false);
cell.lut_cell.equation.set(1, true);
// Map LUT input to input wire used by pseudo pip.
IdString input_bel_pin(bel_data.ports[bel.input_bel_pin]);
cell.cell_bel_pins[IdString(ctx->wire_lut->input_pins[0])].push_back(input_bel_pin);
}
lut_mappers[bel_data.lut_element].cells.push_back(&cell); lut_mappers[bel_data.lut_element].cells.push_back(&cell);
} }
@ -449,13 +457,26 @@ void PseudoPipModel::update_site(const Context *ctx, size_t site)
// FIXME: This lookup is static, consider moving to PseudoPipBel? // FIXME: This lookup is static, consider moving to PseudoPipBel?
IdString bel_name(bel_data.name); IdString bel_name(bel_data.name);
IdString input_bel_pin(bel_data.ports[bel.input_bel_pin]); if (bel.input_bel_pin == -1) {
size_t pin_idx = lut_elements.at(bel_data.lut_element).lut_bels.at(bel_name).pin_to_index.at(input_bel_pin); // No input bel pin (e.g. LUT as constant driver) - check that *any* input is available, i.e. there is
// some room in the LUT equation still
size_t pin_count = lut_elements.at(bel_data.lut_element).lut_bels.at(bel_name).pins.size();
uint32_t pin_mask = (1 << uint32_t(pin_count)) - 1;
uint32_t blocked_inputs = lut_wires_unavailable.at(bel_data.lut_element);
if ((blocked_inputs & pin_mask) == pin_mask) {
blocked_by_lut_eq = true;
break;
}
} else {
IdString input_bel_pin(bel_data.ports[bel.input_bel_pin]);
size_t pin_idx =
lut_elements.at(bel_data.lut_element).lut_bels.at(bel_name).pin_to_index.at(input_bel_pin);
uint32_t blocked_inputs = lut_wires_unavailable.at(bel_data.lut_element); uint32_t blocked_inputs = lut_wires_unavailable.at(bel_data.lut_element);
if ((blocked_inputs & (1 << pin_idx)) != 0) { if ((blocked_inputs & (1 << pin_idx)) != 0) {
blocked_by_lut_eq = true; blocked_by_lut_eq = true;
break; break;
}
} }
} }