From e0ee03184517737bb5a01f98142ad713324bda7c Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Sat, 22 Oct 2022 23:31:04 -0700
Subject: Initial interrupt controller support

---
 io/model.cpp   | 18 ++++++++--------
 isa/decode.cpp | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 isa/isa.h      |  1 +
 3 files changed, 76 insertions(+), 9 deletions(-)

diff --git a/io/model.cpp b/io/model.cpp
index e1b59ea..d6e36f9 100644
--- a/io/model.cpp
+++ b/io/model.cpp
@@ -24,16 +24,16 @@ bool iomodel::interact(std::array<unsigned int, NUM_CTLREGS> &ctlregs) {
     }
 
     bool interrupt = false;
-    if (ctlregs[INT_ENABLE] & 1) {
-        if (ctlregs[TT_INPUT_INT_ENABLE]) {
-            if (ctlregs[TT_BITS] & TTI_FLAG)
-                interrupt = true;
-        }
-        if (ctlregs[TT_OUTPUT_INT_ENABLE]) {
-            if ((ctlregs[TT_BITS] & (TTO_FLAG|TTO_FLAG_OLD)) == TTO_FLAG)
-                interrupt = true;
-        }
+    if (ctlregs[TT_INPUT_INT_ENABLE]) {
+        if (ctlregs[TT_BITS] & TTI_FLAG)
+            interrupt = true;
     }
+    if (ctlregs[TT_OUTPUT_INT_ENABLE]) {
+        if ((ctlregs[TT_BITS] & (TTO_FLAG|TTO_FLAG_OLD)) == TTO_FLAG)
+            interrupt = true;
+    }
+    ctlregs[INT_PENDING] = interrupt;
+    interrupt = interrupt && (ctlregs[INT_ENABLE] & 1);
 
     if (interrupt) {
         ctlregs[DATA_INSTRUCTION_FIELD_SAVED] = ctlregs[DATA_INSTRUCTION_FIELD_BUFFER];
diff --git a/isa/decode.cpp b/isa/decode.cpp
index 1ecb189..d709cf8 100644
--- a/isa/decode.cpp
+++ b/isa/decode.cpp
@@ -73,6 +73,72 @@ instruction_context decode(unsigned int dfifb, unsigned int pc, unsigned int bit
             break;
         case 6: // IOT
             switch ((bits >> 3) & 077) {
+                case 000:
+                    // INTERRUPT CONTROLLER
+                    switch (bits & 07) {
+                        case 0:
+                            // SKON skip if interrupts enabled
+                            inst.read_ctlreg = INT_ENABLE;
+                            inst.possibly_redirects = true;
+                            inst.ef = [](auto &ctx) {
+                                if (ctx.ctlval.value() & 1)
+                                    ctx.next_pc = (ctx.next_pc & 07777) | ((ctx.next_pc + 1) & 07777);
+                            };
+                            break;
+                        case 1:
+                            // ION set int_enable_delay
+                            inst.read_ctlreg = INT_ENABLE;
+                            inst.write_ctlreg = INT_ENABLE;
+                            inst.ef = [](auto &ctx) {
+                                ctx.ctlval.value() |= 2;
+                            };
+                            break;
+                        case 2:
+                            // IOFF clear int_enable and int_enable_delay
+                            inst.write_ctlreg = INT_ENABLE;
+                            inst.ef = [](auto &ctx) {
+                                ctx.ctlval = 0;
+                            };
+                            break;
+                        case 3:
+                            // SRQ skip if pending interrupt
+                            inst.read_ctlreg = INT_PENDING;
+                            inst.possibly_redirects = true;
+                            inst.ef = [](auto &ctx) {
+                                if (ctx.ctlval.value())
+                                    ctx.next_pc = (ctx.next_pc & 07777) | ((ctx.next_pc + 1) & 07777);
+                            };
+                            break;
+                        case 4:
+                            // GTF get flags
+                            inst.ef = [](auto &ctx) {
+                                assert(false);
+                            };
+                            break;
+                        case 5:
+                            // RTF restore flags
+                            inst.ef = [](auto &ctx) {
+                                assert(false);
+                            };
+                            break;
+                        case 6:
+                            // SGT skip if greater than
+                            inst.ef = [](auto &ctx) {
+                                assert(false);
+                            };
+                            break;
+                        case 7:
+                            // CAF clear all flags
+                            inst.ef = [](auto &ctx) {
+                                assert(false);
+                            };
+                            break;
+                        default:
+                            inst.ef = [](auto &ctx) {
+                                assert(false);
+                            };
+                    }
+                    break;
                 case 004:
                     // TELETYPE TELEPRINTER/PUNCH
                     switch (bits & 07) {
diff --git a/isa/isa.h b/isa/isa.h
index 24ed108..1ad5a77 100644
--- a/isa/isa.h
+++ b/isa/isa.h
@@ -8,6 +8,7 @@ enum ctlreg {
     DATA_INSTRUCTION_FIELD_SAVED,   // (df_saved << 3) | if_saved
     HALTED,
     INT_ENABLE,                     // (int_enable_delay << 1) | int_enable
+    INT_PENDING,                    // only meaningful if interrupts disabled
     TT_BITS,                        // see below TT[IO]_* consts
     TT_INPUT_INT_ENABLE,
     TT_OUTPUT_INT_ENABLE,
-- 
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