From eb3fd68203fee7c63245c702914c2acd3332d65a Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Thu, 22 Sep 2022 11:29:07 -0700
Subject: Initial commit.

---
 backend/regfile.h | 132 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 132 insertions(+)
 create mode 100644 backend/regfile.h

(limited to 'backend/regfile.h')

diff --git a/backend/regfile.h b/backend/regfile.h
new file mode 100644
index 0000000..276504c
--- /dev/null
+++ b/backend/regfile.h
@@ -0,0 +1,132 @@
+#pragma once
+
+#include <array>
+
+#include "frontend/decode.h"
+#include "infra/port.h"
+#include "inst.h"
+#include "memory/dram.h"
+
+namespace backend {
+    struct regfile : public infra::sim {
+        infra::port<frontend::decode::restart> *decode_restartp = nullptr;
+
+        infra::port<inst> instp;
+        infra::port<inst> *execp = nullptr;
+        infra::port<inst> writebackp;
+        infra::port<memory::dram::command> *storep = nullptr;
+
+        unsigned int generation_up = 0;
+        unsigned int generation_down = 0;
+
+        std::array<std::uint64_t, 16> regs;
+        std::array<bool, 16> hazards;
+        std::uint64_t pc = 0;
+
+        regfile() {
+            regs.fill(0);
+            hazards.fill(false);
+        }
+
+        void clock() {
+            if (writebackp.can_read() && storep->can_write()) {
+                auto i = writebackp.read();
+                if (i.generation == generation_down) {
+                    pte(i.transaction, "W", fmt::format("writeback gen={} pc={:x}", generation_down, pc));
+                    auto old_pc = pc;
+                    pc = i.linear_next_pc;
+                    switch (i.field[OPCODE]) {
+                        case OP_JUMP_ABS_IF_ZERO:
+                        case OP_JUMP_ABS_IF_NONZERO:
+                            pte(i.transaction, "", fmt::format("jump to {:x}", i.result.value()));
+                            pc = i.result.value();
+                            break;
+                        case OP_EMIT:
+                            pte(i.transaction, "*", fmt::format("emit {}", i.result.value()));
+                            break;
+                        case OP_STORE:
+                            {
+                                memory::dram::command c;
+                                c.transaction = i.transaction;
+                                c.line_address = i.field[SRC1] >> memory::LINE_BYTES_LOG2;
+                                c.write = true;
+                                c.mask.fill(false);
+                                auto offset = i.field[SRC1] & memory::LINE_BYTE_OFFSET_MASK;
+                                pte(i.transaction, "", fmt::format("store [{:x}]={:x} offset={:x}", i.field[SRC1], i.field[SRC2], offset));
+                                for (unsigned int j = 0; j < sizeof(i.field[SRC2]); ++j) {
+                                    c.mask[offset + j] = true;
+                                    c.data[offset + j] = (i.field[SRC2] >> (8 * j)) & 0xff;
+                                }
+                                storep->write(std::move(c));
+                            }
+                            break;
+                        default:
+                            pte(i.transaction, "", fmt::format("wb r{}={:x}", i.field[FLAGS_DST] % regs.size(), i.result.value()));
+                            regs[i.field[FLAGS_DST] % regs.size()] = i.result.value();
+                            hazards[i.field[FLAGS_DST] % regs.size()] = false;
+                            break;
+                    }
+                    if (!i.predicted_next_pc.has_value() || pc != i.predicted_next_pc.value()) {
+                        pte(i.transaction, "", "restart due to pc misprediction");
+                        frontend::decode::restart dr;
+                        dr.new_generation = ++generation_up;
+                        dr.new_pc = pc;
+                        dr.from_pc = old_pc;
+                        decode_restartp->write(std::move(dr));
+                        hazards.fill(false);
+                        ++generation_down;
+                    }
+                }
+            }
+
+            if (instp.can_read() && execp->can_write() && !writebackp.can_read()) {
+                auto i = instp.peek();
+                if (i.generation == generation_up) {
+                    bool hazard = false;
+                    if (!(i.field[FLAGS_DST] & FLAG_IMM1))
+                        hazard |= hazards[i.field[SRC1] % regs.size()];
+                    if (!(i.field[FLAGS_DST] & FLAG_IMM2))
+                        hazard |= hazards[i.field[SRC2] % regs.size()];
+                    switch (i.field[OPCODE]) {
+                        case OP_JUMP_ABS_IF_ZERO:
+                        case OP_JUMP_ABS_IF_NONZERO:
+                        case OP_EMIT:
+                        case OP_STORE:
+                            break;
+                        default:
+                            hazard |= hazards[i.field[FLAGS_DST] % regs.size()];
+                            break;
+                    }
+                    if (!hazard) {
+                        auto i = instp.read();
+                        if (!(i.field[FLAGS_DST] & FLAG_IMM1)) {
+                            auto x = regs[i.field[SRC1] % regs.size()];
+                            pte(i.transaction, "", fmt::format("rf1[{}]={:x}", i.field[SRC1] % regs.size(), x));
+                            i.field[SRC1] = x;
+                        }
+                        if (!(i.field[FLAGS_DST] & FLAG_IMM2)) {
+                            auto x = regs[i.field[SRC2] % regs.size()];
+                            pte(i.transaction, "", fmt::format("rf2[{}]={:x}", i.field[SRC2] % regs.size(), x));
+                            i.field[SRC2] = x;
+                        }
+                        pte(i.transaction, "R", fmt::format("read gen={}", generation_up));
+                        i.generation = generation_down;
+                        switch (i.field[OPCODE]) {
+                            case OP_JUMP_ABS_IF_ZERO:
+                            case OP_JUMP_ABS_IF_NONZERO:
+                            case OP_EMIT:
+                            case OP_STORE:
+                                break;
+                            default:
+                                hazards[i.field[FLAGS_DST] % regs.size()] = true;
+                                break;
+                        }
+                        execp->write(std::move(i));
+                    }
+                } else {
+                    instp.discard();
+                }
+            }
+        }
+    };
+}
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