3 files changed, 23 insertions, 2 deletions

diff --git a/isa/checker.h b/isa/checker.h
index 332c483..571bbc8 100644
--- a/isa/checker.h
+++ b/isa/checker.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <array>
+#include <cstdint>
 #include <map>
 
 #include "io/model.h"
@@ -41,7 +42,7 @@ struct checker {
     unsigned int link = 0;
     unsigned int mq = 0;
     unsigned int pc = 00200;
-    std::array<unsigned int, NUM_CTLREGS> ctlregs;
+    std::array<std::uint_fast32_t, NUM_CTLREGS> ctlregs;
     iomodel &system;
     instruction_context inst;
     funcmem mem;
diff --git a/isa/decode.cpp b/isa/decode.cpp
index 4af9a0d..9563327 100644
--- a/isa/decode.cpp
+++ b/isa/decode.cpp
@@ -140,6 +140,25 @@ instruction_context decode(unsigned int dfifb, unsigned int pc, unsigned int bit
                             break;
                     }
                     break;
+                case 003:
+                    // KEYBOARD
+                    switch (bits & 07) {
+                        case 1:
+                            // KSF skip if TTI flag is set
+                            inst.read_ctlreg = TT_BITS;
+                            inst.possibly_redirects = true;
+                            inst.ef = [](auto &ctx) {
+                                if (ctx.ctlval.value() & TTI_FLAG)
+                                    ctx.next_pc = (ctx.next_pc & ~07777) | ((ctx.next_pc + 1) & 07777);
+                            };
+                            break;
+                        default:
+                            inst.ef = [bits](auto &ctx) {
+                                std::cerr << "unimplemented IOT KB suboperation " << (bits & 07) << "\n";
+                                assert(false);
+                            };
+                    }
+                    break;
                 case 004:
                     // TELETYPE TELEPRINTER/PUNCH
                     switch (bits & 07) {
diff --git a/isa/isa.h b/isa/isa.h
index 1ad5a77..84a783c 100644
--- a/isa/isa.h
+++ b/isa/isa.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <cstdint>
 #include <functional>
 #include <optional>
 
@@ -49,7 +50,7 @@ struct instruction_context {
     unsigned int next_pc;                       // includes IF
     std::optional<unsigned int> init_address;   // includes DF
     std::optional<unsigned int> final_address;  // includes DF
-    std::optional<unsigned int> ctlval;
+    std::optional<std::uint_fast32_t> ctlval;   // control registers may be larger than 16 bits (e.g. TT_BITS)
     std::optional<unsigned int> data;
     std::optional<unsigned int> acc;
     std::optional<bool> link;