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Merge pull request #294 from YosysHQ/gatecat/lut-false-path 

icetime: Ignore false paths through LUTs based on function
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gatecat 2022-03-29 13:34:29 +01:00 committed by GitHub
parent 1d8e1a8f58 b5f9560233
commit 9f66f9ce16
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 38 additions and 5 deletions
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43
icetime/icetime.cc
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@ -59,6 +59,7 @@ std::set<std::tuple<int, int, int>> extra_bits;
std::set<std::string> io_names;
std::map<int, std::string> net_symbols;
std::map<std::string, unsigned> lc_lut_in_mask;
bool get_config_bit(int tile_x, int tile_y, int bit_row, int bit_col)
{
@ -836,6 +837,15 @@ struct TimingAnalysis
}
if (driver_type == "LogicCell40" && (driver_port == "ltout" || driver_port == "lcout")) {
unsigned mask = lc_lut_in_mask.at(driver_cell);
if (inport == "in0" && ((mask & 0x1) == 0))
continue;
if (inport == "in1" && ((mask & 0x2) == 0))
continue;
if (inport == "in2" && ((mask & 0x4) == 0))
continue;
if (inport == "in3" && ((mask & 0x8) == 0))
continue;
if (inport == "carryin")
continue;
}
@ -1221,14 +1231,37 @@ std::string make_lc40(int x, int y, int z)
for (int i = 0; i < 20; i++)
lcbits[i] = get_config_bit(x, y, lcbits_pos[i].first, lcbits_pos[i].second) ? '1' : '0';
static const std::vector<int> lut_perm = {
4, 14, 15, 5, 6, 16, 17, 7, 3, 13, 12, 2, 1, 11, 10, 0,
};
unsigned lut_init = 0;
for (unsigned i = 0; i < lut_perm.size(); i++)
if (lcbits[lut_perm[i]] == '1')
lut_init |= (1U << i);
// FIXME: fill in the '0'
netlist_cell_params[cell]["C_ON"] = stringf("1'b%c", lcbits[8]);
netlist_cell_params[cell]["SEQ_MODE"] = stringf("4'b%c%c%c%c", lcbits[9], '0', '0', '0');
netlist_cell_params[cell]["LUT_INIT"] = stringf("16'b%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c",
lcbits[0], lcbits[10], lcbits[11], lcbits[1],
lcbits[2], lcbits[12], lcbits[13], lcbits[3],
lcbits[7], lcbits[17], lcbits[16], lcbits[6],
lcbits[5], lcbits[15], lcbits[14], lcbits[4]);
std::string init = "16'b";
for (int i = 15; i >= 0; i--)
init += ((lut_init >> i) & 0x1) ? '1' : '0';
netlist_cell_params[cell]["LUT_INIT"] = init;
// Find which LUT inputs are "don't care" in the function, to avoid false paths for bits
// only affecting the carry.
lc_lut_in_mask[cell] = 0;
for (unsigned k = 0; k < 4; k++) {
for (unsigned i = 0; i < 16; i++) {
// If toggling the LUT input makes a difference it's not a don't care
if (((lut_init >> i) & 0x1U) != ((lut_init >> (i ^ (1U << k))) & 0x1U)) {
lc_lut_in_mask[cell] |= (1 << k);
break;
}
}
}
if (lcbits[8] == '1')
{