From d97b32ac6a2ccca3704f567b12ab0378dc7e8dac Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Sun, 16 Oct 2022 17:19:25 -0700
Subject: Nearly-working version of TTY output

---
 isa/decode.cpp | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 68 insertions(+), 8 deletions(-)

(limited to 'isa')

diff --git a/isa/decode.cpp b/isa/decode.cpp
index d24632b..cb6a694 100644
--- a/isa/decode.cpp
+++ b/isa/decode.cpp
@@ -23,7 +23,7 @@ instruction_context decode(unsigned int dfifb, unsigned int pc, unsigned int bit
             inst.need_read_acc = true;
             inst.need_write_acc = true;
             inst.ef = [](auto &ctx) {
-                ctx.acc = ctx.acc.value() & ctx.data.value();
+                ctx.acc = ctx.acc.value() & ctx.data.value() & 07777;
             };
             break;
         case 1: // TAD
@@ -44,7 +44,7 @@ instruction_context decode(unsigned int dfifb, unsigned int pc, unsigned int bit
             inst.possibly_redirects = true;
             inst.ef = [](auto &ctx) {
                 ctx.data = (ctx.data.value() + 1) & 07777;
-                if (*ctx.data)
+                if (*ctx.data == 0)
                     ctx.next_pc = (ctx.next_pc & ~07777) | ((ctx.next_pc + 1) & 07777);
             };
             break;
@@ -72,9 +72,69 @@ instruction_context decode(unsigned int dfifb, unsigned int pc, unsigned int bit
             };
             break;
         case 6: // IOT
-            inst.ef = [](auto &ctx) {
-                assert(false);
-            };
+            switch ((bits >> 3) & 077) {
+                case 004:
+                    switch (bits & 07) {
+                        case 0:
+                            inst.write_ctlreg = TT_OUTPUT;
+                            inst.ef = [](auto &ctx) {
+                                ctx.ctlval = 0x600;
+                            };
+                            break;
+                        case 1:
+                            inst.read_ctlreg = TT_OUTPUT;
+                            inst.possibly_redirects = true;
+                            inst.ef = [](auto &ctx) {
+                                if (ctx.ctlval.value() & 0x200)
+                                    ctx.next_pc = (ctx.next_pc & ~07777) | ((ctx.next_pc + 1) & 07777);
+                            };
+                            break;
+                        case 2:
+                            inst.write_ctlreg = TT_OUTPUT;
+                            inst.ef = [](auto &ctx) {
+                                ctx.ctlval = 0;
+                            };
+                            break;
+                        case 4:
+                            inst.need_read_acc = true;
+                            inst.read_ctlreg = TT_OUTPUT;
+                            inst.write_ctlreg = TT_OUTPUT;
+                            inst.ef = [](auto &ctx) {
+                                auto &x = ctx.ctlval.value();
+                                x &= ~0x1ff;
+                                x |= (ctx.acc.value() & 0xff) ^ 0x80; // 0x7f instead of 0xff for real PDP-8 IO
+                                x |= 0x100;
+                            };
+                            break;
+                        case 5:
+                            inst.possibly_redirects = true;
+                            // FIXME this instruction wants to read both TT_OUTPUT and TT_INPUT
+                            inst.ef = [](auto &ctx) {
+                                assert(false);
+                            };
+                            break;
+                        case 6:
+                            inst.need_read_acc = true;
+                            inst.read_ctlreg = TT_OUTPUT;
+                            inst.write_ctlreg = TT_OUTPUT;
+                            inst.ef = [](auto &ctx) {
+                                auto &x = ctx.ctlval.value();
+                                x &= ~0x7ff;
+                                x |= (ctx.acc.value() & 0xff) ^ 0x80;
+                                x |= 0x100;
+                            };
+                            break;
+                        default:
+                            inst.ef = [](auto &ctx) {
+                                assert(false);
+                            };
+                    }
+                    break;
+                default:
+                    inst.ef = [](auto &ctx) {
+                        assert(false);
+                    };
+            }
             break;
         case 7: // OPR
             if ((bits & 0400) == 0000) {
@@ -93,7 +153,7 @@ instruction_context decode(unsigned int dfifb, unsigned int pc, unsigned int bit
                 inst.ef = [cla, cll, cma, cml, rar, ral, bsw, iac](auto &ctx) {
                     if (cla) ctx.acc = 0;
                     if (cll) ctx.link = 0;
-                    if (cma) ctx.acc = ~ctx.acc.value();
+                    if (cma) ctx.acc = ~ctx.acc.value() & 07777;
                     if (cml) ctx.link = !ctx.link.value();
                     if (iac) {
                         if (++ctx.acc.value() == 0) ctx.link = !ctx.link.value();
@@ -139,7 +199,7 @@ instruction_context decode(unsigned int dfifb, unsigned int pc, unsigned int bit
                     assert(!osr);
                     if (hlt) ctx.ctlval = 1;
                     if (skip)
-                        ctx.next_pc = (ctx.next_pc & 070000) | ((ctx.next_pc + 1) & 007777);
+                        ctx.next_pc = (ctx.next_pc & ~07777) | ((ctx.next_pc + 1) & 07777);
                 };
             } else if ((bits & 0411) == 0410) {
                 bool cla = bits & 0200;
@@ -163,7 +223,7 @@ instruction_context decode(unsigned int dfifb, unsigned int pc, unsigned int bit
                     assert(!osr);
                     if (hlt) ctx.ctlval = 1;
                     if (skip)
-                        ctx.next_pc = (ctx.next_pc & 070000) | ((ctx.next_pc + 1) & 007777);
+                        ctx.next_pc = (ctx.next_pc & ~07777) | ((ctx.next_pc + 1) & 07777);
                 };
             } else if ((bits & 0401) == 0401) {
                 bool cla = bits & 0200;
-- 
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