Gowin. Fix BSRAM block selection.

In the images generated by Gowin IDE, the signals for dynamic BSRAM
block selection (BLKSEL[2:0]) are not always connected directly to the
ports - some chips add LUT2, LUT3 or LUT4 to turn these signals into
Clock Enable.  Apparently there are chips with an error in the operation
of these ports.

Here we make such a decoder instead of using ports directly.

Signed-off-by: YRabbit <[email protected]>

himbaechel/uarch/gowin/constids.inc

@@ -889,6 +889,7 @@ X(DID)
 X(WRE)
 
 // BSRAM
+X(BLK_SEL)
 X(BSRAM_SUBTYPE)
 X(WRITE_MODE)
 X(READ_MODE)

himbaechel/uarch/gowin/gowin.h

@@ -98,6 +98,7 @@ NPNR_PACKED_STRUCT(struct Extra_chip_data_POD {
     static constexpr int32_t HAS_SP32 = 1;
     static constexpr int32_t NEED_SP_FIX = 2;
     static constexpr int32_t NEED_BSRAM_OUTREG_FIX = 4;
+    static constexpr int32_t NEED_BLKSEL_FIX = 8;
 });
 
 } // namespace

himbaechel/uarch/gowin/gowin_arch_gen.py

@@ -15,9 +15,10 @@
 BEL_FLAG_SIMPLE_IO = 0x100
 
 # Chip flags
-CHIP_HAS_SP32             = 0x1
-CHIP_NEED_SP_FIX          = 0x2
+CHIP_HAS_SP32              = 0x1
+CHIP_NEED_SP_FIX           = 0x2
 CHIP_NEED_BSRAM_OUTREG_FIX = 0x4
+CHIP_NEED_BLKSEL_FIX       = 0x8
 
 # Z of the bels
 # sync with C++ part!
@@ -1021,6 +1022,8 @@ def main():
             chip_flags |= CHIP_NEED_SP_FIX;
         if "NEED_BSRAM_OUTREG_FIX" in db.chip_flags:
             chip_flags |= CHIP_NEED_BSRAM_OUTREG_FIX;
+        if "NEED_BLKSEL_FIX" in db.chip_flags:
+            chip_flags |= CHIP_NEED_BLKSEL_FIX;
 
     X = db.cols;
     Y = db.rows;

himbaechel/uarch/gowin/gowin_utils.cc

@@ -130,6 +130,12 @@ bool GowinUtils::need_BSRAM_OUTREG_fix(void)
     return extra->chip_flags & Extra_chip_data_POD::NEED_BSRAM_OUTREG_FIX;
 }
 
+bool GowinUtils::need_BLKSEL_fix(void)
+{
+    const Extra_chip_data_POD *extra = reinterpret_cast<const Extra_chip_data_POD *>(ctx->chip_info->extra_data.get());
+    return extra->chip_flags & Extra_chip_data_POD::NEED_BLKSEL_FIX;
+}
+
 std::unique_ptr<CellInfo> GowinUtils::create_cell(IdString name, IdString type)
 {
     NPNR_ASSERT(!ctx->cells.count(name));

himbaechel/uarch/gowin/gowin_utils.h

@@ -38,6 +38,7 @@ struct GowinUtils
     bool have_SP32(void);
     bool need_SP_fix(void);
     bool need_BSRAM_OUTREG_fix(void);
+    bool need_BLKSEL_fix(void);
 
     // DSP
     inline int get_dsp_18_z(int z) const { return z & (~3); }

himbaechel/uarch/gowin/pack.cc

@@ -1331,6 +1331,70 @@ struct GowinPacker
         }
     }
 
+    // We solve the BLKSEL problems that are observed on some chips by
+    // connecting the BLKSEL ports to constant networks so that this BSRAM will
+    // be selected, the actual selection is made by manipulating the Clock
+    // Enable pin using a LUT-based decoder.
+    void bsram_fix_blksel(CellInfo *ci, std::vector<std::unique_ptr<CellInfo>> &new_cells)
+    {
+        // is BSRAM enabled
+        NetInfo *ce_net = ci->getPort(id_CE);
+        if (ce_net == nullptr || ce_net->name == ctx->id("$PACKER_GND")) {
+            return;
+        }
+
+        // port name, BLK_SEL parameter for this port
+        std::vector<std::pair<IdString, int>> dyn_blksel;
+
+        int blk_sel_parameter = ci->params.at(id_BLK_SEL).as_int64();
+        for (int i = 0; i < 3; ++i) {
+            IdString pin_name = ctx->idf("BLKSEL[%d]", i);
+            NetInfo *net = ci->getPort(pin_name);
+            if (net == nullptr || net->name == ctx->id("$PACKER_GND") || net->name == ctx->id("$PACKER_VCC")) {
+                continue;
+            }
+            dyn_blksel.push_back(std::make_pair(pin_name, (blk_sel_parameter >> i) & 1));
+        }
+
+        if (dyn_blksel.empty()) {
+            return;
+        }
+
+        if (ctx->verbose) {
+            log_info("  apply the BSRAM BLKSEL fix\n");
+        }
+
+        // Make a decoder
+        auto lut_cell = gwu.create_cell(create_aux_name(ci->name, 0, "_blksel_lut$"), id_LUT4);
+        CellInfo *lut = lut_cell.get();
+        lut->addInput(id_I3);
+        ci->movePortTo(id_CE, lut, id_I3);
+        lut->addOutput(id_F);
+        ci->connectPorts(id_CE, lut, id_F);
+
+        NetInfo *vcc_net = ctx->nets.at(ctx->id("$PACKER_VCC")).get();
+        NetInfo *vss_net = ctx->nets.at(ctx->id("$PACKER_GND")).get();
+
+        // Connected CE to I3 to make it easy to calculate the decoder
+        int init = 0x100; // CE == 0 -->  F = 0
+                          // CE == 1 -->  F = decoder result
+        int idx = 0;
+        for (auto &port : dyn_blksel) {
+            IdString lut_input_name = ctx->idf("I%d", idx);
+            ci->movePortTo(port.first, lut, lut_input_name);
+            if (port.second) {
+                init <<= (1 << idx);
+                ci->connectPort(port.first, vcc_net);
+            } else {
+                ci->connectPort(port.first, vss_net);
+            }
+            ++idx;
+        }
+        lut->setParam(id_INIT, init);
+
+        new_cells.push_back(std::move(lut_cell));
+    }
+
     // Some chips cannot, for some reason, use internal BSRAM registers to
     // implement READ_MODE=1'b1 (pipeline) with a word width other than 32 or
     // 36 bits.
@@ -1729,6 +1793,11 @@ struct GowinPacker
             bsram_fix_outreg(ci, new_cells);
         }
 
+        // Some chips have problems with BLKSEL ports
+        if (gwu.need_BLKSEL_fix()) {
+            bsram_fix_blksel(ci, new_cells);
+        }
+
         // XXX UG285-1.3.6_E Gowin BSRAM & SSRAM User Guide:
         // For GW1N-9/GW1NR-9/GW1NS-4 series, 32/36-bit SP/SPX9 is divided into two
         // SP/SPX9s, which occupy two BSRAMs.