From a59407a215d6112c2e20b1a746b33742209e5f87 Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Sun, 16 Oct 2022 16:24:49 -0700
Subject: Support for log-based event model

---
 io/event.h   | 18 ++++++++++++++++++
 io/model.cpp | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 io/model.h   | 15 +++++++++++++++
 3 files changed, 82 insertions(+)
 create mode 100644 io/event.h
 create mode 100644 io/model.cpp
 create mode 100644 io/model.h

(limited to 'io')

diff --git a/io/event.h b/io/event.h
new file mode 100644
index 0000000..02f3fab
--- /dev/null
+++ b/io/event.h
@@ -0,0 +1,18 @@
+#pragma once
+
+#include <map>
+
+#include "isa/isa.h"
+
+struct event {
+    ctlreg reg;
+    unsigned int mask;
+    unsigned int value;
+    event(ctlreg reg, unsigned int value, unsigned int mask=~0)
+        : reg(reg)
+        , mask(mask)
+        , value(value)
+    { }
+};
+
+typedef std::multimap<std::uint64_t, event> event_log;
diff --git a/io/model.cpp b/io/model.cpp
new file mode 100644
index 0000000..dd55ce6
--- /dev/null
+++ b/io/model.cpp
@@ -0,0 +1,49 @@
+#include <array>
+#include <cstdint>
+#include <iostream>
+#include <utility>
+
+#include "io/model.h"
+#include "isa/isa.h"
+
+bool iomodel::interact(std::array<unsigned int, NUM_CTLREGS> &ctlregs) {
+    auto [ebegin, eend] = log.equal_range(time);
+    for (auto e = ebegin; e != eend; ++e) {
+        auto &r = ctlregs[e->second.reg];
+        r &= ~e->second.mask;
+        r |= e->second.value;
+    }
+
+    ++time;
+
+    if (ctlregs[TT_OUTPUT] & 0x100) {
+        // PDP-8 doesn't really have support for 8-bit output, this is Jules' contribution
+        std::cout << (char)((ctlregs[TT_OUTPUT] & 0xff) ^ 0x80);
+        ctlregs[TT_OUTPUT] &= ~0x1ff;
+        log.emplace(time + TT_OUTPUT_DELAY, event(TT_OUTPUT, 0x200, 0));
+    }
+
+    bool interrupt = false;
+    if (ctlregs[INT_ENABLE] & 1) {
+        if (ctlregs[TT_INPUT_INT_ENABLE]) {
+            if (ctlregs[TT_INPUT] & 0x100)
+                interrupt = true;
+        }
+        if (ctlregs[TT_OUTPUT_INT_ENABLE]) {
+            if (!(ctlregs[TT_OUTPUT] & 0x400) && (ctlregs[TT_OUTPUT] & 0x200))
+                interrupt = true;
+        }
+    }
+
+    if (interrupt) {
+        ctlregs[DATA_INSTRUCTION_FIELD_SAVED] = ctlregs[DATA_INSTRUCTION_FIELD_BUFFER];
+        ctlregs[DATA_INSTRUCTION_FIELD_BUFFER] = 0;
+        ctlregs[HALTED] = 0;
+        ctlregs[INT_ENABLE] = 0;
+        ctlregs[TT_OUTPUT] = (ctlregs[TT_OUTPUT] & 0x200) * 3;
+    } else {
+        ctlregs[INT_ENABLE] = (ctlregs[INT_ENABLE] >> 1) * 3;
+    }
+
+    return interrupt;
+};
diff --git a/io/model.h b/io/model.h
new file mode 100644
index 0000000..86fb086
--- /dev/null
+++ b/io/model.h
@@ -0,0 +1,15 @@
+#pragma once
+
+#include <array>
+#include <cstdint>
+
+#include "io/event.h"
+#include "isa/isa.h"
+
+struct iomodel {
+    static constexpr unsigned int TT_OUTPUT_DELAY = 100;
+
+    event_log log;
+    std::uint64_t time = 0;
+    bool interact(std::array<unsigned int, NUM_CTLREGS> &ctlregs);
+};
-- 
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