1 files changed, 11 insertions, 2 deletions

diff --git a/isa/isa.h b/isa/isa.h
index bea484e..24ed108 100644
--- a/isa/isa.h
+++ b/isa/isa.h
@@ -8,14 +8,23 @@ enum ctlreg {
     DATA_INSTRUCTION_FIELD_SAVED,   // (df_saved << 3) | if_saved
     HALTED,
     INT_ENABLE,                     // (int_enable_delay << 1) | int_enable
-    TT_INPUT,                       // (tti_flag << 8) | tti_buffer
+    TT_BITS,                        // see below TT[IO]_* consts
     TT_INPUT_INT_ENABLE,
-    TT_OUTPUT,                      // {tto_flag_old, tto_flag, tto_tx, tto_data}
     TT_OUTPUT_INT_ENABLE,
 
     NUM_CTLREGS,
 };
 
+// TT_BITS
+static constexpr unsigned int TTI_FLAG = 1 << 0;
+static constexpr unsigned int TTO_TX = 1 << 1;
+static constexpr unsigned int TTO_FLAG = 1 << 2;
+static constexpr unsigned int TTO_FLAG_OLD = 1 << 3;
+static constexpr unsigned int TTI_DATA_SHIFT = 8;
+static constexpr unsigned int TTO_DATA_SHIFT = 16;
+static constexpr unsigned int TTI_DATA = 0xff << TTI_DATA_SHIFT;
+static constexpr unsigned int TTO_DATA = 0xff << TTO_DATA_SHIFT;
+
 struct instruction_context {
     // Known statically at decode time
     bool need_indirect_load = false;    // final_address = mem[init_address]