From 6ffe43a8ccee6f3e2d6fda5062901f16c54ddaad Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Mon, 31 Oct 2022 19:26:35 -0700
Subject: Level-trigger on TTO_FLAG instead of edge-trigger.

---
 io/model.cpp   | 3 +--
 isa/decode.cpp | 6 +++---
 isa/isa.h      | 1 -
 3 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/io/model.cpp b/io/model.cpp
index 3bea59e..fcabbd2 100644
--- a/io/model.cpp
+++ b/io/model.cpp
@@ -29,7 +29,7 @@ bool iomodel::interact(std::array<std::uint_fast32_t, NUM_CTLREGS> &ctlregs) {
             interrupt = true;
     }
     if (ctlregs[TT_INT_ENABLE]) {
-        if ((ctlregs[TT_BITS] & (TTO_FLAG|TTO_FLAG_OLD)) == TTO_FLAG)
+        if (ctlregs[TT_BITS] & TTO_FLAG)
             interrupt = true;
     }
     ctlregs[INT_PENDING] = interrupt;
@@ -40,7 +40,6 @@ bool iomodel::interact(std::array<std::uint_fast32_t, NUM_CTLREGS> &ctlregs) {
         ctlregs[DATA_INSTRUCTION_FIELD_BUFFER] = 0;
         ctlregs[HALTED] = 0;
         ctlregs[INT_ENABLE] = 0;
-        ctlregs[TT_BITS] |= (ctlregs[TT_BITS] & TTO_FLAG) ? TTO_FLAG_OLD : 0;
     } else {
         ctlregs[INT_ENABLE] = (ctlregs[INT_ENABLE] >> 1) * 3;
     }
diff --git a/isa/decode.cpp b/isa/decode.cpp
index c11679c..1496364 100644
--- a/isa/decode.cpp
+++ b/isa/decode.cpp
@@ -185,7 +185,7 @@ instruction_context decode(unsigned int dfifb, unsigned int pc, unsigned int bit
                             inst.read_ctlreg = TT_BITS;
                             inst.write_ctlreg = TT_BITS;
                             inst.ef = [](auto &ctx) {
-                                ctx.ctlval.value() |= TTO_FLAG | TTO_FLAG_OLD;
+                                ctx.ctlval.value() |= TTO_FLAG;
                             };
                             break;
                         case 1:
@@ -202,7 +202,7 @@ instruction_context decode(unsigned int dfifb, unsigned int pc, unsigned int bit
                             inst.read_ctlreg = TT_BITS;
                             inst.write_ctlreg = TT_BITS;
                             inst.ef = [](auto &ctx) {
-                                ctx.ctlval.value() &= ~TTO_FLAG & ~TTO_FLAG_OLD;
+                                ctx.ctlval.value() &= ~TTO_FLAG;
                             };
                             break;
                         case 4:
@@ -235,7 +235,7 @@ instruction_context decode(unsigned int dfifb, unsigned int pc, unsigned int bit
                             inst.ef = [](auto &ctx) {
                                 auto &x = ctx.ctlval.value();
                                 auto chr = ctx.acc.value();
-                                x &= ~TTO_FLAG & ~TTO_FLAG_OLD & ~TTO_DATA;
+                                x &= ~TTO_FLAG & ~TTO_DATA;
                                 x |= (chr << TTO_DATA_SHIFT) & TTO_DATA;
                                 x |= TTO_TX;
                             };
diff --git a/isa/isa.h b/isa/isa.h
index 6484cd8..69f8b2a 100644
--- a/isa/isa.h
+++ b/isa/isa.h
@@ -30,7 +30,6 @@ const std::map<std::string, ctlreg> ctlreg_map = {
 static constexpr std::uint_fast32_t TTI_FLAG = 1 << 0;
 static constexpr std::uint_fast32_t TTO_TX = 1 << 1;
 static constexpr std::uint_fast32_t TTO_FLAG = 1 << 2;
-static constexpr std::uint_fast32_t TTO_FLAG_OLD = 1 << 3;
 static constexpr unsigned int TTI_DATA_SHIFT = 8;
 static constexpr unsigned int TTO_DATA_SHIFT = 16;
 static constexpr std::uint_fast32_t TTI_DATA = 0xff << TTI_DATA_SHIFT;
-- 
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