From de713c17dd16b31585e7709ea1f381b89d90bbb0 Mon Sep 17 00:00:00 2001
From: Peter Ferrie <peter.ferrie@gmail.com>
Date: Wed, 20 Apr 2016 09:35:47 -0700
Subject: [PATCH] v2 with partial track support

---
 0BOOT.S   | 30 +++++++++++++++++++++++++++---
 DOS33L.S  | 37 +++++++++++++++++++++++++++++++++++++
 readme.md |  1 +
 3 files changed, 65 insertions(+), 3 deletions(-)
 create mode 100644 DOS33L.S

diff --git a/0BOOT.S b/0BOOT.S
index df93393..fbfd734 100644
--- a/0BOOT.S
+++ b/0BOOT.S
@@ -1,5 +1,5 @@
 ;bootable zpage seek/read
-;copyright (c) Peter Ferrie 2015
+;copyright (c) Peter Ferrie 2015-16
 ;thanks to 4am for inspiration and testing
 ;assemble using ACME
 !cpu 6502
@@ -8,7 +8,8 @@
         tracks    = $d1         ;user-defined
         address   = $d1         ;user-defined
         entry     = $d1d1       ;user-defined
-        version   = 1
+        sectors   = $00         ;user-defined, sectors to load from partial track (increase tracks first)
+        version   = 2
 
         ;memory usage:
         ;256 bytes ($200-2FF) static table
@@ -62,17 +63,35 @@
         bne     +               ;branch always
 *=$839
         jsr     preread
+        lda     #>(entry-1)
+        pha
+        lda     #<(entry-1)
+        pha
+        ldx     #<((tracks*16)+sectors)
+        lda     #address
         jmp     $bf00           ;DOS 3.3 launcher entrypoint
 
         ;build read/seek call-sequence per track
-
 +
+!if sectors>0 {
+        txa
+        pha
+        lda     #<initsec
+        pha
+        txa
+        clc
+        bcc     ++
+}
+
 -       txa
         bcc     +               ;set initially by LSR above
         pha
         pha
         !byte   $c9             ;CMP masks SEC, clears carry on even rounds
 +       sec                     ;SEC is reached on odd rounds
+!if sectors>0 {
+++
+}
         pha
         lda     #<(seek-1)
         pha                     ;push seek twice for two phases
@@ -143,6 +162,11 @@ count
 
 inittrk
         ldx     #$f0
+initsec
+!if sectors>0 {
+        !byte   $2c
+        ldx     #<(-sectors)
+}
         stx     <count
 rdpage
         lda     #address
diff --git a/DOS33L.S b/DOS33L.S
new file mode 100644
index 0000000..392266a
--- /dev/null
+++ b/DOS33L.S
@@ -0,0 +1,37 @@
+;0boot DOS 3.3 launcher support
+;copyright (c) Peter Ferrie 2016
+;assemble using ACME
+!cpu 6502
+!to "dos33l",plain
+;place on sector 1
+*=$BF00
+        stx     sectors
+        sta     address
+index   ldy     #0
+-       lda     xlatsec, y
+        sta     sector
+        lda     #>iocb
+        ldy     #<iocb
+        jsr     $bd00
+        ldy     index + 1
+        iny
+        tya
+        and     #$0f
+        sta     index + 1
+        tay
+        bne     +
+        inc     track
++       inc     address
+        dec     sectors
+        bne     -
+        rts
+
+sectors !byte   $d1
+xlatsec !byte   0, 7, $e, 6, $d, 5, $c, 4, $b, 3, $a, 2, 9, 1, 8, $f
+iocb    !byte   1, $60, 1, 0
+track   !byte   1
+sector  !byte   0
+        !byte   <dct, >dct, 0
+address !byte   0
+        !byte   0, 0, 1, 0, 0, $60, 1
+dct     !byte   1, $ef, $d8, 0
diff --git a/readme.md b/readme.md
index 79031fd..a3afabc 100644
--- a/readme.md
+++ b/readme.md
@@ -5,5 +5,6 @@ fast bootable Read Track/Sector routine.
 - full-track read in one revolution
 - runs entirely from zpage
 - can load up to 11 complete tracks
+- can load up to 12 additional sectors ($0400-bfff)
 - DOS 3.3 Launcher compatible
 - requires only 3 pages in memory