From 474104085c5a761983e7abd60633ea44aedb0f5d Mon Sep 17 00:00:00 2001
From: Peter Evans <peter@modul8r.com>
Date: Tue, 20 Mar 2018 14:06:26 -0500
Subject: [PATCH] Reorganize encoded sizes/routines to align with reference
 nibble output

(This is comparing to the output that we see from dsk2nib.)
---
 include/apple2.dd.h  |  2 +-
 include/apple2.enc.h |  4 ++--
 src/apple2.enc.c     | 22 +++++++++++++++++-----
 3 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/include/apple2.dd.h b/include/apple2.dd.h
index bb74d90..f30c5ef 100644
--- a/include/apple2.dd.h
+++ b/include/apple2.dd.h
@@ -43,7 +43,7 @@ enum apple2_dd_mode {
  * it is nibbilized with 6-and-2 encoding.
  */
 #define _140K_ 143360
-#define _140K_NIB_ 223440
+#define _140K_NIB_ 233008
 
 /*
  * And this is the length of a disk that has been formatted as a nibble
diff --git a/include/apple2.enc.h b/include/apple2.enc.h
index 9d41925..4e26a8b 100644
--- a/include/apple2.enc.h
+++ b/include/apple2.enc.h
@@ -37,13 +37,13 @@
  * An encoded sector is 396 bytes long, and is comprised of a sector
  * header plus padding bytes both before _and_ after the data field.
  */
-#define ENC_ESECTOR 0x18c
+#define ENC_ESECTOR 0x1a0
 
 /*
  * An encoded track contains 16 sectors, as mentioned for ENC_DTRACK.
  * But it also contains some additional padding (48 bytes-worth).
  */
-#define ENC_ETRACK 0x18f0
+#define ENC_ETRACK 0x1a00
 
 /*
  * A sector header consists of some byte markers--all byte markers in
diff --git a/src/apple2.enc.c b/src/apple2.enc.c
index 08fe44e..f74be12 100644
--- a/src/apple2.enc.c
+++ b/src/apple2.enc.c
@@ -33,6 +33,14 @@ static vm_8bit gcr62[] = {
     0xed, 0xee, 0xef, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff, // 30
 };
 
+/*
+ * Define the physical sector order in which we write encoded data
+ */
+static int physical_order[] = {
+    0x0, 0xD, 0xB, 0x9, 0x7, 0x5, 0x3, 0x1,
+    0xE, 0xC, 0xA, 0x8, 0x6, 0x4, 0x2, 0xF,
+};
+
 /*
  * Encode the given DOS-formatted segment with 6-and-2 encoding. This
  * can work for both DOS 3.3 and ProDOS images, but would fail with DOS
@@ -119,7 +127,11 @@ apple2_enc_track(int sectype, vm_segment *dest, vm_segment *src,
     }
 
     for (sect = 0; sect < 16; sect++) {
-        soff = toff + (ENC_DSECTOR * apple2_dd_sector_num(sectype, sect));
+        int logsec = apple2_dd_sector_num(sectype, sect);
+        int physec = physical_order[sect];
+
+        soff = toff + (ENC_DSECTOR * logsec);
+        doff = orig + (ENC_ESECTOR * physec) + 48;
 
         // Each sector has a header with some metadata, plus some
         // markers and padding.
@@ -127,7 +139,7 @@ apple2_enc_track(int sectype, vm_segment *dest, vm_segment *src,
         doff += apple2_enc_sector(dest, src, doff, soff);
     }
 
-    return doff - orig;
+    return ENC_ETRACK;
 }
 
 /*
@@ -232,8 +244,8 @@ apple2_enc_sector(vm_segment *dest, vm_segment *src,
     vm_segment_set(dest, doff++, 0xaa);
     vm_segment_set(dest, doff++, 0xeb);
 
-    // At the conclusion of a sector, we write 27 self-sync bytes.
-    for (i = 0; i < 27; i++) {
+    // At the conclusion of a sector, we write 48 self-sync bytes.
+    for (i = 0; i < 48; i++) {
         vm_segment_set(dest, doff++, 0xff);
     }
 
@@ -290,7 +302,7 @@ apple2_enc_sector_header(vm_segment *seg, int off,
 
     // Write six (exactly six!) self-sync bytes following the epilogue,
     // because the Disk II controller/RWTS method expect to find it.
-    for (int i = 0; i < 6; i++) {
+    for (int i = 0; i < 5; i++) {
         vm_segment_set(seg, off++, 0xff);
     }