From 23a1e64e9f0f7674d48228795647aa0387686577 Mon Sep 17 00:00:00 2001
From: "Christopher A. Mosher" <cmosher01@gmail.com>
Date: Wed, 19 Dec 2018 23:52:21 -0500
Subject: [PATCH] implement LSS writing (to WOZ TRKS in memory)

---
 src/diskcontroller.cpp | 16 ++++++++++------
 src/diskcontroller.h   |  1 +
 src/wozfile.cpp        |  2 +-
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/src/diskcontroller.cpp b/src/diskcontroller.cpp
index 5ddd081..b6fae26 100644
--- a/src/diskcontroller.cpp
+++ b/src/diskcontroller.cpp
@@ -90,8 +90,11 @@ void DiskController::tick() {
     rotateCurrentDisk();
 
     // run two LSS cycles = 2MHz
+
     stepLss();
+    // pulse lasts only 500 nanoseconds (1 LSS clock cycle), so clear it now:
     this->currentDrive->clearPulse();
+
     stepLss();
 }
 
@@ -109,8 +112,14 @@ void DiskController::stepLss() {
     this->seq = cmd & 0xF0u;
 
     // LSS command functions (UA2, 9-15, Table 9.3)
-//    printf("%02x:", cmd);
     if (cmd & 8u) {
+        if (cmd & 3u) {
+            if (this->write) {
+                const bool one = (seq&0x80u) != (this->prev_seq&0x80u);
+                this->prev_seq = seq;
+                this->currentDrive->writeBit(one);
+            }
+        }
         switch (cmd & 3u) {
         case 3:
             this->dataRegister = this->dataBusReadOnlyCopy;
@@ -118,15 +127,10 @@ void DiskController::stepLss() {
         case 2:
             this->dataRegister >>= 1;
             this->dataRegister |= (isWriteProtected() << 7);
-            // TODO how to handle writing?
             break;
         case 1:
             this->dataRegister <<= 1;
             this->dataRegister |= ((cmd & 4u) >> 2);
-//            printf(this->dataRegister & 0x80u ? "\x1b[30;42m" : "\x1b[30;43m");
-//            printf("%02X\x1b[0m ", this->dataRegister);
-//            if (this->dataRegister & 0x80u) printf("\n");
-            // TODO how to handle writing?
             break;
         }
     } else {
diff --git a/src/diskcontroller.h b/src/diskcontroller.h
index ef3fa1f..45fc65b 100644
--- a/src/diskcontroller.h
+++ b/src/diskcontroller.h
@@ -58,6 +58,7 @@ private:
         // For ease of use, we store the 4-bit seq number in the _high order_ nibble here.
         // On the real Apple the read pulse goes thru this LS174 too, but we don't emulate that here.
 
+        std::uint8_t prev_seq; // remember previous seq, to determine if A7 changes (indicating write a 1 bit)
         std::uint8_t t; // used to keep track of 4 MPU cycles
 
         // TODO for a rev. 0 motherboard, the disk controller will auto reset the CPU (see UA2, 9-13)
diff --git a/src/wozfile.cpp b/src/wozfile.cpp
index 3541dbe..70c97ba 100644
--- a/src/wozfile.cpp
+++ b/src/wozfile.cpp
@@ -254,7 +254,7 @@ static std::uint8_t cb(std::uint8_t bit) {
 
 /*
  * Rotate the floppy disk by one bit.
- * In real life we don't care what track we're one, but for the
+ * In real life we don't care what track we're on, but for the
  * emulator we need to know. This is because the tracks within the
  * WOZ file could be different lengths. So in order to know when
  * we need to loop back to the beginning of the track (circular