8 files changed, 759 insertions, 133 deletions

diff --git a/Makefile b/Makefile
index 9e84cc8..ed96817 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,11 @@ CXX ?= g++
 IWYU ?= iwyu
 CHRONIC ?= chronic
 
-CXXFLAGS := -Wall -Werror -std=c++20 -fPIC -iquote . ${OPTIMIZE} ${DEBUG}
+PKGS := fmt
+PKG_FLAGS := $(shell pkg-config --cflags ${PKGS})
+PKG_LIBS := -Wl,--push-state,--as-needed $(shell pkg-config --libs ${PKGS}) -Wl,--pop-state
+
+CXXFLAGS := -Wall -Werror -std=c++20 -fPIC -iquote . ${PKG_FLAGS} ${OPTIMIZE} ${DEBUG}
 
 .DEFAULT_GOAL := all
 
@@ -24,7 +28,7 @@ endef
 export GITTAGCPP
 
 ifneq ($(shell which ${IWYU}),)
-iwyu = ${CHRONIC} ${IWYU} -Xiwyu --error ${CXXFLAGS} $(1)
+iwyu = ${CHRONIC} ${IWYU} -Xiwyu --error -Xiwyu --mapping_file=tools/iwyu.imp ${CXXFLAGS} $(1)
 else
 $(warning Not using IWYU)
 iwyu =
@@ -42,29 +46,32 @@ $(call libname,$(1).a): $(patsubst %.cpp,build/%.o,$(wildcard $(1)/*.cpp))
 
 $(call libname,$(1).so): $(patsubst %.cpp,build/%.o,$(wildcard $(1)/*.cpp))
         @mkdir -p $$(dir $$@)
-        $${CXX} $${CXXFLAGS} -shared -o $$@ $$+
+        $${CXX} $${CXXFLAGS} -shared -o $$@ $$+ ${PKG_LIBS}
 
 PARTARS += $(call libname,$(1).a)
 PARTSOS += $(call libname,$(1).so)
 
-else
+endif
 
-$(call libname,$(1).cpp):
+ifdef iwyu
+
+build/$(1)/iwyu.cpp:
         @mkdir -p $$(dir $$@)
         @tools/iwyu-header $$(wildcard $(1)/*.h) > $$@
         @$$(call iwyu,$$@)
-.PHONY: $(call libname,$(1).cpp)
+.PHONY: build/$(1)/iwyu.cpp
 
-EXTRA_TARGETS += $(call libname,$(1).cpp)
+IWYU_CPPS += build/$(1)/iwyu.cpp
 
 endif
 
 endef
 
 PARTS := $(patsubst ./%,%,$(shell find -mindepth 1 -type d -\( -name .\* -prune -o -name build -prune -o -name tools -prune -o -print -\)))
+
 PARTARS :=
 PARTSOS :=
-EXTRA_TARGETS :=
+IWYU_CPPS :=
 
 $(foreach part,${PARTS},$(eval $(call mklib,${part})))
 
@@ -73,7 +80,7 @@ MAINOBJS += build/git-tag.o
 
 $(info )
 
-all: ${EXTRA_TARGETS} issim issim-static
+all: ${IWYU_CPPS} issim issim-static
 
 issim: build/issim-dynamic
         @ln -sf $< $@
@@ -85,11 +92,11 @@ issim-static: build/issim-static
 
 build/issim-dynamic: ${MAINOBJS} ${PARTSOS}
         @mkdir -p $(dir $@)
-        ${CXX} ${CXXFLAGS} -o $@ $+
+        ${CXX} ${CXXFLAGS} -o $@ $+ ${PKG_LIBS}
 
 build/issim-static: ${MAINOBJS} ${PARTARS}
         @mkdir -p $(dir $@)
-        ${CXX} ${CXXFLAGS} -o $@ $+
+        ${CXX} ${CXXFLAGS} -o $@ $+ ${PKG_LIBS}
 
 clean:
         rm -rf build issim issim-static
diff --git a/aisa/aisa.h b/aisa/aisa.h
index 3c260c1..4488529 100644
--- a/aisa/aisa.h
+++ b/aisa/aisa.h
@@ -1,20 +1,67 @@
 #pragma once
 
 #include <cstdint>
+#include <memory>
 #include <optional>
+#include <string>
 #include <utility>
 #include <vector>
 
 namespace aisa {
 
+    using addr_t = std::uint64_t;
+    using byte_t = std::uint8_t;
     using regnum_t = std::uint_fast64_t;
     using regval_t = std::uint64_t;
 
+    struct Task;
+
+    struct ISA {
+        virtual ~ISA() { }
+
+        virtual std::pair<std::unique_ptr<const Task>, regval_t> initial_task() const = 0;
+    };
+
+    struct Step;
+
+    struct Task {
+        regnum_t environment;
+
+        virtual ~Task() { }
+
+        virtual std::string disasm() const = 0;
+
+        virtual std::optional<std::pair<std::unique_ptr<const Step>, regval_t>> step(regval_t environment_val) const { return {}; }
+    };
+
+    struct MemInfo {
+        addr_t physical_addr;
+        addr_t size;
+    };
+
+    struct Wires {
+        std::vector<regval_t> source_vals;
+        std::vector<byte_t> memory_val;
+        bool aborted = false;
+        std::vector<regval_t> destination_vals;
+        std::optional<std::pair<std::unique_ptr<const Task>, regval_t>> new_task;
+    };
+
+    enum class MOp {
+        NONE,
+        LOAD,
+        STORE,
+    };
+
     struct Step {
         std::optional<std::pair<regnum_t, regval_t>> predicate;
         std::vector<regnum_t> source_regs;
         std::vector<regnum_t> destination_regs;
 
+        virtual ~Step() { }
+
+        virtual std::string disasm(const Wires *w = nullptr) const = 0;
+
         std::optional<regnum_t> predicate_reg() const
         {
             if (predicate.has_value())
@@ -29,7 +76,10 @@ namespace aisa {
             return {};
         }
 
-        virtual std::vector<regval_t> compute_destinations(const std::vector<regval_t> &source_vals) const = 0;
+        MOp mop = MOp::NONE;
+
+        virtual MemInfo meminfo(const Wires &wires) const { return {}; }
+        virtual void evaluate(Wires &wires) const { };
     };
 
 }
diff --git a/aisa/async.h b/aisa/async.h
new file mode 100644
index 0000000..42e99e7
--- /dev/null
+++ b/aisa/async.h
@@ -0,0 +1,225 @@
+#pragma once
+
+#include <coroutine>
+#include <optional>
+#include <utility>
+#include <memory>
+#include <vector>
+
+#include "aisa/aisa.h"
+#include "aisa/coroutine.h" // IWYU pragma: export
+
+namespace aisa {
+
+    template<typename CRTP> struct AsyncEval {
+        CRTP & crtp() noexcept { return static_cast<CRTP &>(*this); }
+
+        task<regval_t> async_load_reg(regnum_t rn)
+        {
+            while (true) {
+                if (auto rv = crtp().load_reg(rn); rv.has_value())
+                    co_return *rv;
+                co_await std::suspend_always{};
+            }
+        }
+
+        task<void> async_store_reg(regnum_t rn, regval_t rv)
+        {
+            while (true) {
+                if (crtp().store_reg(rn, rv))
+                    co_return;
+                co_await std::suspend_always{};
+            }
+        }
+
+        task<void> async_fetch_mem(byte_t *bytes, addr_t physical_addr, addr_t size)
+        {
+            while (true) {
+                if (crtp().fetch_mem(bytes, physical_addr, size))
+                    co_return;
+                co_await std::suspend_always{};
+            }
+        }
+
+        task<void> async_store_mem(addr_t physical_addr, const byte_t *bytes, addr_t size)
+        {
+            while (true) {
+                if (crtp().store_mem(physical_addr, bytes, size))
+                    co_return;
+                co_await std::suspend_always{};
+            }
+        }
+
+        task<bool> async_predicate(const Step &step)
+        {
+            if (step.predicate.has_value()) {
+                regval_t pval = co_await crtp().async_load_reg(step.predicate->first);
+                co_return pval == step.predicate->second;
+            }
+            co_return true;
+        }
+
+        task<void> async_load_source_registers(const Step &step, Wires &w)
+        {
+            w.source_vals.resize(step.source_regs.size());
+            for (unsigned int i = 0; i < step.source_regs.size(); ++i)
+                w.source_vals[i] = co_await crtp().async_load_reg(step.source_regs[i]);
+        }
+
+        task<void> async_load_source_memory(const Step &step, const MemInfo &mi, Wires &w)
+        {
+            w.memory_val.resize(mi.size);
+            co_await crtp().async_fetch_mem(w.memory_val.data(), mi.physical_addr, mi.size);
+        }
+
+        task<void> async_load_sources(const Step &step, Wires &w)
+        {
+            co_await crtp().async_load_source_registers(step, w);
+
+            if (step.mop == MOp::LOAD) {
+                auto mi = step.meminfo(w);
+                co_await crtp().async_load_source_memory(step, mi, w);
+            }
+        }
+
+        task<void> async_write_destination_registers(const Step &step, const Wires &w)
+        {
+            for (unsigned int i = 0; i < step.destination_regs.size(); ++i)
+                co_await crtp().async_store_reg(step.destination_regs[i], w.destination_vals[i]);
+        }
+
+        task<void> async_write_destination_memory(const Step &step, const MemInfo &mi, const Wires &w)
+        {
+            co_await crtp().async_store_mem(mi.physical_addr, w.memory_val.data(), mi.size);
+        }
+
+        task<void> async_write_destinations(const Step &step, const Wires &w)
+        {
+            if (w.aborted)
+                co_return;
+
+            co_await crtp().async_write_destination_registers(step, w);
+
+            if (step.mop == MOp::STORE) {
+                auto mi = step.meminfo(w);
+                co_await crtp().async_write_destination_memory(step, mi, w);
+            }
+        }
+
+        task<void> async_push_task(std::unique_ptr<const Task> &&task)
+        {
+            while (true) {
+                if (crtp().push_task(std::move(task)))
+                    co_return;
+                co_await std::suspend_always{};
+            }
+        }
+
+        task<void> async_new_task(std::unique_ptr<const Task> &&task, regval_t environment_val)
+        {
+            auto rn = task->environment;
+            co_await crtp().async_push_task(std::move(task));
+            co_await crtp().async_store_reg(rn, environment_val);
+        }
+
+        task<Wires> async_run_step(const Step &step)
+        {
+            Wires w;
+
+            if (!co_await crtp().async_predicate(step))
+                co_return std::move(w);
+
+            co_await crtp().async_load_sources(step, w);
+
+            step.evaluate(w);
+
+            co_await crtp().async_write_destinations(step, w);
+
+            if (w.new_task.has_value())
+                co_await crtp().async_new_task(std::move(w.new_task->first), w.new_task->second);
+
+            co_return std::move(w);
+        }
+
+        task<const Task *> async_top_task()
+        {
+            while (true) {
+                if (auto rv = crtp().top_task(); rv.has_value())
+                    co_return &**rv;
+                co_await std::suspend_always{};
+            }
+        }
+
+        task<void> async_pop_task()
+        {
+            while (true) {
+                if (crtp().pop_task())
+                    co_return;
+                co_await std::suspend_always{};
+            }
+        }
+
+        task<std::optional<std::unique_ptr<const Step>>> async_fetch_step()
+        {
+            auto task = co_await crtp().async_top_task();
+
+            auto rn = task->environment;
+            auto rv = co_await crtp().async_load_reg(rn);
+
+            auto step = task->step(rv);
+            if (step.has_value()) {
+                co_await crtp().async_store_reg(rn, step->second);
+                co_return std::move(step->first);
+            } else {
+                co_await crtp().async_pop_task();
+                co_return {};
+            }
+        }
+
+        task<std::pair<std::unique_ptr<const Step>, Wires>> async_fetch_and_run_step()
+        {
+            while (true) {
+                if (auto step = co_await crtp().async_fetch_step(); step.has_value()) {
+                    auto wires = co_await crtp().async_run_step(**step);
+                    co_return {std::move(*step), std::move(wires)};
+                }
+            }
+        }
+
+        task<void> async_run_subtree()
+        {
+            while (true) {
+                if (auto step = co_await crtp().async_fetch_step(); step.has_value())
+                    co_await crtp().async_run_step_and_subtree(**step);
+                else
+                    break;
+            }
+        }
+
+        task<Wires> async_run_step_and_subtree(const Step &step)
+        {
+            auto w = co_await crtp().async_run_step(step);
+
+            if (w.new_task.has_value())
+                co_await crtp().async_run_subtree();
+
+            co_return std::move(w);
+        }
+
+        task<void> async_setup_initial_task(const ISA &isa)
+        {
+            auto task = isa.initial_task();
+
+            co_await crtp().async_new_task(std::move(task.first), task.second);
+        }
+
+        task<void> async_run(const ISA &isa)
+        {
+            co_await crtp().async_setup_initial_task(isa);
+
+            co_await crtp().async_run_subtree();
+        }
+
+    };
+
+}
diff --git a/aisa/eval.h b/aisa/eval.h
deleted file mode 100644
index a301e93..0000000
--- a/aisa/eval.h
+++ /dev/null
@@ -1,65 +0,0 @@
-#pragma once
-
-#include <coroutine>
-#include <memory>
-#include <optional>
-#include <utility>
-#include <vector>
-
-#include "aisa/aisa.h"
-#include "aisa/coroutine.h" // IWYU pragma: export
-
-namespace aisa {
-
-    template<typename CRTP> struct EvalState {
-        struct EvalContext {
-            task<void> coroutine;
-
-            bool resume() { return coroutine(); }
-        };
-
-        CRTP & crtp() noexcept { return static_cast<CRTP &>(*this); }
-
-        task<regval_t> async_load_reg(regnum_t rn)
-        {
-            while (true) {
-                if (auto rv = crtp().load_reg(rn); rv.has_value())
-                    co_return *rv;
-                co_await std::suspend_always{};
-            }
-        }
-
-        task<void> async_store_reg(regnum_t rn, regval_t rv)
-        {
-            while (true) {
-                if (crtp().store_reg(rn, rv))
-                    co_return;
-                co_await std::suspend_always{};
-            }
-        }
-
-        task<void> async_evaluate(EvalContext &contex, const Step &step)
-        {
-            if (step.predicate.has_value()) {
-                regval_t pval = co_await async_load_reg(step.predicate->first);
-                if (pval != step.predicate->second)
-                    co_return;
-            }
-            std::vector<regval_t> source_vals;
-            source_vals.reserve(step.source_regs.size());
-            for (unsigned int i = 0; i < step.source_regs.size(); ++i)
-                source_vals.emplace_back(co_await async_load_reg(step.source_regs[i]));
-            auto destination_vals = step.compute_destinations(source_vals);
-            for (unsigned int i = 0; i < step.destination_regs.size(); ++i)
-                co_await async_store_reg(step.destination_regs[i], destination_vals[i]);
-        }
-
-        std::unique_ptr<EvalContext> operator()(const Step &step)
-        {
-            auto context = std::make_unique<EvalContext>();
-            context->coroutine = async_evaluate(*context, step);
-            return context;
-        }
-    };
-
-}
diff --git a/aisa/simple-models.h b/aisa/simple-models.h
new file mode 100644
index 0000000..89e8752
--- /dev/null
+++ b/aisa/simple-models.h
@@ -0,0 +1,95 @@
+#pragma once
+
+#include <algorithm>
+#include <array>
+#include <cstring>
+#include <deque>
+#include <map>
+#include <memory>
+#include <optional>
+#include <utility>
+#include <vector>
+
+#include "aisa/aisa.h"
+
+namespace aisa {
+
+    template<unsigned int PAGE_BITS=10> struct PagedMem {
+        using page_t = std::array<byte_t, 1 << PAGE_BITS>;
+
+        static const addr_t PAGE_SIZE = 1 << PAGE_BITS;
+        static const addr_t PAGE_MASK = PAGE_SIZE - 1;
+
+        std::map<addr_t, page_t> pages;
+
+        bool fetch_mem(byte_t *bytes, addr_t addr, addr_t size)
+        {
+            if (size == 0)
+                return true;
+            auto page_base = addr >> PAGE_BITS;
+            auto page_offset = addr & PAGE_MASK;
+            auto size_here = std::min(size, PAGE_SIZE - page_offset);
+            if (auto page = pages.find(page_base); page != pages.end())
+                std::memcpy(bytes, page->second.data() + page_offset, size_here);
+            else
+                std::memset(bytes, 0, size_here);
+            return fetch_mem(bytes + size_here, addr + size_here, size - size_here);
+        }
+
+        bool store_mem(addr_t addr, const byte_t *bytes, addr_t size)
+        {
+            if (size == 0)
+                return true;
+            auto page_base = addr >> PAGE_BITS;
+            auto page_offset = addr & PAGE_MASK;
+            auto size_here = std::min(size, PAGE_SIZE - page_offset);
+            std::memcpy(pages[page_base].data() + page_offset, bytes, size_here);
+            return store_mem(addr + size_here, bytes + size_here, size - size_here);
+        }
+    };
+
+    struct TaskStack {
+        std::deque<std::unique_ptr<const Task>> tasks;
+
+        bool pop_task()
+        {
+            if (tasks.empty())
+                return false;
+            tasks.pop_back();
+            return true;
+        }
+
+        bool push_task(std::unique_ptr<const Task> &&task)
+        {
+            tasks.emplace_back(std::move(task));
+            return true;
+        }
+
+        std::optional<const Task *> top_task()
+        {
+            if (tasks.empty())
+                return {};
+            return tasks.back().get();
+        }
+    };
+
+    struct VectorRF {
+        std::vector<std::optional<regval_t>> rf;
+
+        std::optional<regval_t> load_reg(regnum_t rn) const
+        {
+            if (rf.size() <= rn)
+                return {};
+            return rf[rn];
+        }
+
+        bool store_reg(regnum_t rn, regval_t rv)
+        {
+            if (rf.size() <= rn)
+                rf.resize(rn + 1);
+            rf[rn] = rv;
+            return true;
+        }
+    };
+
+}
diff --git a/isa/fib/fib.h b/isa/fib/fib.h
new file mode 100644
index 0000000..13801c8
--- /dev/null
+++ b/isa/fib/fib.h
@@ -0,0 +1,288 @@
+#pragma once
+
+#include <fmt/core.h>
+#include <memory>
+#include <optional>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "aisa/aisa.h"
+
+namespace isa::fib {
+
+    namespace Reg {
+        enum {
+            ENV_TOP,
+            ENV_FIB,
+
+            AREG,
+            ATMP,
+
+            PC,
+
+            A,
+            B,
+            Q,
+        };
+
+        const char *disasm(aisa::regnum_t x)
+        {
+            switch (x) {
+                case ENV_TOP: return "ENV_TOP";
+                case ENV_FIB: return "ENV_FIB";
+                case AREG: return "AREG";
+                case ATMP: return "ATMP";
+                case PC: return "PC";
+                case A: return "A";
+                case B: return "B";
+                case Q: return "Q";
+                default: return "???";
+            }
+        }
+    }
+
+    struct StepAdd : public aisa::Step {
+        StepAdd(aisa::regnum_t q, aisa::regnum_t a, aisa::regnum_t b)
+        {
+            source_regs.resize(2);
+            source_regs[0] = a;
+            source_regs[1] = b;
+
+            destination_regs.resize(1);
+            destination_regs[0] = q;
+        }
+
+        std::string disasm(const aisa::Wires *w) const override
+        {
+            if (w)
+                return fmt::format("{}({}) <- {}({}) + {}({})", Reg::disasm(destination_regs[0]), w->destination_vals[0], Reg::disasm(source_regs[0]), w->source_vals[0], Reg::disasm(source_regs[1]), w->source_vals[1]);
+            return fmt::format("{} <- {} + {}", Reg::disasm(destination_regs[0]), Reg::disasm(source_regs[0]), Reg::disasm(source_regs[1]));
+        }
+
+        void evaluate(aisa::Wires &w) const override
+        {
+            w.destination_vals.resize(1);
+            w.destination_vals[0] = w.source_vals[0] + w.source_vals[1];
+        }
+    };
+
+    struct StepAddImmediate : public aisa::Step {
+        aisa::regval_t x;
+
+        StepAddImmediate(aisa::regnum_t q, aisa::regnum_t a, aisa::regval_t x)
+            :x(x)
+        {
+            source_regs.resize(1);
+            source_regs[0] = a;
+
+            destination_regs.resize(1);
+            destination_regs[0] = q;
+        }
+
+        std::string disasm(const aisa::Wires *w) const override
+        {
+            if (w)
+                return fmt::format("{}({}) <- {}({}) + {}", Reg::disasm(destination_regs[0]), w->destination_vals[0], Reg::disasm(source_regs[0]), w->source_vals[0], x);
+            return fmt::format("{} <- {} + {}", Reg::disasm(destination_regs[0]), Reg::disasm(source_regs[0]), x);
+        }
+
+        void evaluate(aisa::Wires &w) const override
+        {
+            w.destination_vals.resize(1);
+            w.destination_vals[0] = w.source_vals[0] + x;
+        }
+    };
+
+    template<unsigned int WORD> struct StepLoad : public aisa::Step {
+        StepLoad(aisa::regnum_t q, aisa::regnum_t a)
+        {
+            source_regs.resize(1);
+            source_regs[0] = a;
+
+            destination_regs.resize(1);
+            destination_regs[0] = q;
+
+            mop = aisa::MOp::LOAD;
+        }
+
+        std::string disasm(const aisa::Wires *w) const override
+        {
+            if (w)
+                return fmt::format("{}({}) <- [{}({})]", Reg::disasm(destination_regs[0]), w->destination_vals[0], Reg::disasm(source_regs[0]), w->source_vals[0]);
+            return fmt::format("{} <- [{}]", Reg::disasm(destination_regs[0]), Reg::disasm(source_regs[0]));
+        }
+
+        aisa::MemInfo meminfo(const aisa::Wires &w) const override
+        {
+            aisa::MemInfo mi;
+            mi.physical_addr = w.source_vals[0] * WORD;
+            mi.size = WORD;
+            return mi;
+        }
+
+        void evaluate(aisa::Wires &w) const override
+        {
+            w.destination_vals.resize(1);
+            auto &q = w.destination_vals[0];
+            q = 0;
+            for (unsigned int i = 0; i < WORD; ++i)
+                q |= static_cast<aisa::regval_t>(w.memory_val[i]) << (8 * i);
+        }
+    };
+
+    struct StepMove : public aisa::Step {
+        StepMove(aisa::regnum_t q, aisa::regnum_t a)
+        {
+            source_regs.resize(1);
+            source_regs[0] = a;
+
+            destination_regs.resize(1);
+            destination_regs[0] = q;
+        }
+
+        std::string disasm(const aisa::Wires *w) const override
+        {
+            if (w)
+                return fmt::format("{}({}) <- {}({})", Reg::disasm(destination_regs[0]), w->destination_vals[0], Reg::disasm(source_regs[0]), w->source_vals[0]);
+            return fmt::format("{} <- {}", Reg::disasm(destination_regs[0]), Reg::disasm(source_regs[0]));
+        }
+
+        void evaluate(aisa::Wires &w) const override
+        {
+            w.destination_vals = w.source_vals;
+        }
+    };
+
+    struct StepMoveImmediate : public aisa::Step {
+        aisa::regval_t x;
+
+        StepMoveImmediate(aisa::regnum_t q, aisa::regval_t x)
+            : x(x)
+        {
+            destination_regs.resize(1);
+            destination_regs[0] = q;
+        }
+
+        std::string disasm(const aisa::Wires *w) const override
+        {
+            if (w)
+                return fmt::format("{}({}) <- {}", Reg::disasm(destination_regs[0]), w->destination_vals[0], x);
+            return fmt::format("{} <- {}", Reg::disasm(destination_regs[0]), x);
+        }
+
+        void evaluate(aisa::Wires &w) const override
+        {
+            w.destination_vals.resize(1);
+            w.destination_vals[0] = x;
+        }
+    };
+
+    template<typename Subtask> struct StepSpawn : public aisa::Step {
+        void evaluate(aisa::Wires &w) const override
+        {
+            w.new_task = {std::make_unique<Subtask>(), 0};
+        }
+
+        std::string disasm(const aisa::Wires *w) const override
+        {
+            return fmt::format("spawn");
+        }
+    };
+
+    template<unsigned int WORD> struct StepStore : public aisa::Step {
+        StepStore(aisa::regnum_t a, aisa::regnum_t d)
+        {
+            source_regs.resize(2);
+            source_regs[0] = a;
+            source_regs[1] = d;
+
+            mop = aisa::MOp::STORE;
+        }
+
+        std::string disasm(const aisa::Wires *w) const override
+        {
+            if (w)
+                return fmt::format("[{}({})] <- {}({})", Reg::disasm(source_regs[0]), w->source_vals[0], Reg::disasm(source_regs[1]), w->source_vals[1]);
+            return fmt::format("[{}] <- {}", Reg::disasm(source_regs[0]), Reg::disasm(source_regs[1]));
+        }
+
+        aisa::MemInfo meminfo(const aisa::Wires &w) const override
+        {
+            aisa::MemInfo mi;
+            mi.physical_addr = w.source_vals[0] * WORD;
+            mi.size = WORD;
+            return mi;
+        }
+
+        void evaluate(aisa::Wires &w) const override
+        {
+            w.memory_val.resize(WORD);
+            for (unsigned int i = 0; i < WORD; ++i)
+                w.memory_val[i] = w.source_vals[1] >> (8 * i);
+        }
+    };
+
+    template<unsigned int WORD> struct TaskFib : public aisa::Task {
+        TaskFib()
+        {
+            environment = Reg::ENV_FIB;
+        }
+
+        std::string disasm() const override
+        {
+            return "fib";
+        }
+
+        std::optional<std::pair<std::unique_ptr<const aisa::Step>, aisa::regval_t>> step(aisa::regval_t env) const override
+        {
+            switch (env) {
+                case 0: return {{std::make_unique<StepLoad<WORD>>(Reg::A, Reg::PC), env+1}};
+                case 1: return {{std::make_unique<StepAddImmediate>(Reg::PC, Reg::PC, 1), env+1}};
+                case 2: return {{std::make_unique<StepLoad<WORD>>(Reg::B, Reg::PC), env+1}};
+                case 3: return {{std::make_unique<StepAddImmediate>(Reg::AREG, Reg::PC, 1), env+1}};
+                case 4: return {{std::make_unique<StepAdd>(Reg::Q, Reg::A, Reg::B), env+1}};
+                case 5: return {{std::make_unique<StepStore<WORD>>(Reg::AREG, Reg::Q), env+1}};
+            }
+
+            return {};
+        }
+    };
+
+    template<unsigned int WORD> struct TaskTop : public aisa::Task {
+        TaskTop()
+        {
+            environment = Reg::ENV_TOP;
+        }
+
+        std::string disasm() const override
+        {
+            return "top";
+        }
+
+        std::optional<std::pair<std::unique_ptr<const aisa::Step>, aisa::regval_t>> step(aisa::regval_t env) const override
+        {
+            switch (env) {
+                case 0: return {{std::make_unique<StepMoveImmediate>(Reg::PC, 0), env+1}};
+                case 1: return {{std::make_unique<StepMoveImmediate>(Reg::AREG, 0), env+1}};
+                case 2: return {{std::make_unique<StepMoveImmediate>(Reg::ATMP, 0), env+1}};
+                case 3: return {{std::make_unique<StepStore<WORD>>(Reg::AREG, Reg::ATMP), env+1}};
+                case 4: return {{std::make_unique<StepMoveImmediate>(Reg::AREG, 1), env+1}};
+                case 5: return {{std::make_unique<StepMoveImmediate>(Reg::ATMP, 1), env+1}};
+                case 6: return {{std::make_unique<StepStore<WORD>>(Reg::AREG, Reg::ATMP), env+1}};
+                case 7: return {{std::make_unique<StepSpawn<TaskFib<WORD>>>(), env}};
+            }
+
+            return {};
+        }
+    };
+
+    template<unsigned int WORD=1> struct Fib : public aisa::ISA {
+        std::pair<std::unique_ptr<const aisa::Task>, aisa::regval_t> initial_task() const override
+        {
+            auto t = std::make_unique<TaskTop<WORD>>();
+            return {std::move(t), 0};
+        }
+    };
+
+}
diff --git a/main.cpp b/main.cpp
index e88d740..f172226 100644
--- a/main.cpp
+++ b/main.cpp
@@ -1,89 +1,112 @@
-#include <initializer_list>
+#include <fmt/core.h>
 #include <iostream>
-#include <map>
 #include <memory>
 #include <optional>
 #include <string>
-#include <type_traits>
 #include <utility>
-#include <vector>
 
 #include "aisa/aisa.h"
-#include "aisa/eval.h"
+#include "aisa/async.h"
+#include "aisa/simple-models.h"
 #include "git-tag.h"
+#include "isa/fib/fib.h"
+
+const bool show_mem_fetch = false;
+const bool show_mem_store = true;
+const bool show_regs = false;
+const bool show_steps = true;
+const bool show_tasks = false;
 
 int main(int argc, const char *argv[])
 {
     std::cout << "Version " << GIT_TAG << "\n";
 
-    struct CopyStep : public aisa::Step {
-        CopyStep(std::pair<aisa::regnum_t, aisa::regval_t> pred, const std::initializer_list<std::pair<aisa::regnum_t, aisa::regnum_t>> &regs)
+    isa::fib::Fib<2> fib;
+
+    struct Eval : public aisa::AsyncEval<Eval>, aisa::PagedMem<>, aisa::TaskStack, aisa::VectorRF {
+        bool fetch_mem(aisa::byte_t *bytes, aisa::addr_t addr, aisa::addr_t size)
         {
-            predicate = std::move(pred);
-            source_regs.reserve(regs.size());
-            destination_regs.reserve(regs.size());
-            for (const auto &rp : regs) {
-                source_regs.emplace_back(rp.first);
-                destination_regs.emplace_back(rp.second);
+            if (aisa::PagedMem<>::fetch_mem(bytes, addr, size)) {
+                if (show_mem_fetch) {
+                    fmt::print("\t\t\t");
+                    for (; size; --size)
+                        fmt::print("{:02x} ", *bytes++);
+                    fmt::print("= [{:x}]\n", addr);
+                }
+                return true;
             }
+            return false;
         }
-
-        std::vector<aisa::regval_t> compute_destinations(const std::vector<aisa::regval_t> &source_vals) const override
+        bool store_mem(aisa::addr_t addr, const aisa::byte_t *bytes, aisa::addr_t size)
         {
-            return source_vals;
+            if (aisa::PagedMem<>::store_mem(addr, bytes, size)) {
+                if (show_mem_store) {
+                    fmt::print("\t\t\t[{:x}] =", addr);
+                    for (; size; --size)
+                        fmt::print(" {:02x}", *bytes++);
+                    fmt::print("\n");
+                }
+                return true;
+            }
+            return false;
         }
-    } step{{123, 456}, {{1, 2}, {3, 4}, {5, 6}}};
 
-    struct State : public aisa::EvalState<State> {
-        std::map<aisa::regnum_t, aisa::regval_t> regs;
+        bool store_reg(aisa::regnum_t rn, aisa::regval_t rv)
+        {
+            if (aisa::VectorRF::store_reg(rn, rv)) {
+                if (show_regs)
+                    fmt::print(".{} = {}\n", isa::fib::Reg::disasm(rn), rv);
+                return true;
+            }
+            return false;
+        }
 
-        std::optional<aisa::regval_t> load_reg(aisa::regnum_t rn)
+        bool push_task(std::unique_ptr<const aisa::Task> &&task)
         {
-            std::cout << "state.load_reg(" << rn << ") = ";
-            if (auto x = regs.find(rn); x != regs.end()) {
-                std::cout << x->second << "\n";
-                return x->second;
+            auto d = task->disasm();
+            if (aisa::TaskStack::push_task(std::move(task))) {
+                if (show_tasks)
+                    fmt::print("\t\t*** ENTER {} ***\n", d);
+                return true;
             }
-            std::cout << "(not available)\n";
-            return {};
+            return false;
         }
 
-        bool store_reg(aisa::regnum_t rn, aisa::regval_t rv)
+        bool pop_task()
         {
-            std::cout << "state.store_reg(" << rn << " <- " << rv << ")\n";
-            regs[rn] = rv;
-            return true;
+            if (aisa::TaskStack::pop_task()) {
+                if (show_tasks)
+                    fmt::print("\t\t *** LEAVE ***\n");
+                return true;
+            }
+            return false;
         }
-    } state;
+    } eval;
 
-    auto t = state.async_load_reg(999);
-    std::cout << "run\n"; t();
-    std::cout << "run\n"; t();
-    std::cout << "run\n"; t();
-    std::cout << "set regs[999] = 54321\n"; state.store_reg(999, 54321);
-    std::optional<aisa::regval_t> result;
-    while (!result.has_value()) {
-        std::cout << "run\n";
-        result = t();
+    if (!eval.async_setup_initial_task(fib)()) {
+        fmt::print("Failed to complete initial setup.\n");
+        return 1;
     }
-    std::cout << "result = " << *result << "\n";
 
-    std::cout << "\n\n\n";
+    while (true) {
+        auto res = eval.async_fetch_and_run_step()();
+        if (res.has_value()) {
+            auto &es = *res;
+            if (es.first) {
+                auto &step = *es.first;
+                auto &w = es.second;
+                if (show_steps)
+                    fmt::print("\t{}\n", step.disasm(&w));
+            } else {
+                break;
+            }
+        } else {
+            fmt::print("Failed to complete step.\n");
+            return 2;
+        }
+    }
 
-    auto w = state(step);
-    std::cout << "run\n"; w->resume();
-    std::cout << "run\n"; w->resume();
-    std::cout << "run\n"; w->resume();
-    std::cout << "set predicate (valid)\n"; state.store_reg(step.predicate->first, step.predicate->second);
-    std::cout << "run\n"; w->resume();
-    std::cout << "run\n"; w->resume();
-    std::cout << "run\n"; w->resume();
-    std::cout << "set regs (all)\n";
-    for (int i = 0; i < 10; ++i)
-        state.store_reg(i, 1000 + i);
-    for (bool done = false; !done; done = w->resume())
-        std::cout << "run\n";
-    std::cout << "huzzah!\n";
+    fmt::print("Functional model exited.\n");
 
     return 0;
 }
diff --git a/tools/iwyu.imp b/tools/iwyu.imp
new file mode 100644
index 0000000..b48e049
--- /dev/null
+++ b/tools/iwyu.imp
@@ -0,0 +1,3 @@
+[
+    { include: [ "<ext/alloc_traits.h>", private, "<vector>", public ] },
+]