Add TRS-80 support.

doc/disk-trs80.md

@@ -0,0 +1,34 @@
+Disk: TRS-80
+============
+
+The TRS-80 models I, III and IV (but not the II, 100, 2000, Colour Computer
+or Pocket Computer) was a popular line of Z80-based home computers made by
+Tandy Corporation and sold by Radio Shack. There were some of the first
+generation of domestic micromputers, with the Model I released in 1978.
+
+There were a myriad of different floppy disk interfaces, some produced by
+Tandy and some by third parties, using all the various combinations of 40-
+and 80-track, FM, MFM, etc.
+
+Luckily the encoding scheme was mostly compatible with the IBM scheme, with a
+few minor variations: when using FM encoding, the TRS-80 wrote the sectors on
+track 17 (where the directory was) with a non-standard DAM byte.
+
+FluxEngine's IBM reader can handle TRS-80 disks natively.
+
+Reading discs
+-------------
+
+Just do:
+
+```
+.obj/fe-readibm
+```
+
+You should end up with an `ibm.img` of the appropriate size. It's a simple
+array of sectors in JV1 format.
+
+If you've got a 40-track disk, use `-s :t=0-79x2`.
+
+If you've got a single density disk, use `--read-fm=true`. (Double density is
+the default.)

doc/index.md

@@ -93,6 +93,7 @@ Here's the table.
 | [Brother 120kB](disk-brother.html)     |  🦄   |        |                                     |
 | [Brother 240kB](disk-brother.html)     |  🦄   |   🦄   |                                     |
 | [Macintosh 800kB](disk-macintosh.html) |  🦖   |        | and probably the 400kB too          |
+| [TRS-80](disk-trs80.html)              |  🦖   |        | a minor variation of the IBM scheme |
 | [Victor 9000](disk-victor9k.html)      |  🦖   |        | experimental, probably buggy        |
 {: .datatable }
 

lib/ibm/decoder.cc

@@ -42,6 +42,8 @@ SectorVector AbstractIbmDecoder::decodeToSectors(const RawRecordVector& rawRecor
 
             case IBM_DAM1:
             case IBM_DAM2:
+            case IBM_TRS80DAM1:
+            case IBM_TRS80DAM2:
             {
                 if (!idamValid)
                     break;
@@ -88,21 +90,46 @@ int IbmFmDecoder::recordMatcher(uint64_t fifo) const
      * clock:  X X - X - X X X  = 0xd7
      * data:    X X X X X X - - = 0xfc
      * 
-     * ID record:
+     * IDAM record:
      * flux:   XXXX-X-X-XXXXXX- = 0xf57e
      * clock:  X X - - - X X X  = 0xc7
      * data:    X X X X X X X - = 0xfe
      * 
-     * ID record:
+     * DAM1 record:
+     * flux:   XXXX-X-X-XX-X-X- = 0xf56a
+     * clock:  X X - - - X X X  = 0xc7
+     * data:    X X X X X - - - = 0xf8
+     * 
+     * DAM2 record:
      * flux:   XXXX-X-X-XX-XXXX = 0xf56f
      * clock:  X X - - - X X X  = 0xc7
-     * data:    X X X X X - X X = 0xfe
+     * data:    X X X X X - X X = 0xfb
+     * 
+     * TRS80DAM1 record:
+     * flux:   XXXX-X-X-XX-X-XX = 0xf56b
+     * clock:  X X - - - X X X  = 0xc7
+     * data:    X X X X X - - X = 0xf9
+     * 
+     * TRS80DAM2 record:
+     * flux:   XXXX-X-X-XX-XXX- = 0xf56c
+     * clock:  X X - - - X X X  = 0xc7
+     * data:    X X X X X - X - = 0xfa
      */
          
     uint16_t masked = fifo & 0xffff;
-    if ((masked == 0xf77a) || (masked == 0xf57e) || (masked == 0xf56f))
-        return 16;
-    return 0;
+    switch (masked)
+    {
+        case 0xf77a:
+        case 0xf57e:
+        case 0xf56a:
+        case 0xf56f:
+        case 0xf56b:
+        case 0xf56c:
+            return 16;
+        
+        default:
+            return 0;
+    }
 }
 
 int IbmMfmDecoder::recordMatcher(uint64_t fifo) const

lib/ibm/ibm.h

@@ -12,6 +12,8 @@
 #define IBM_IDAM_LEN   7      /* plus prologue */
 #define IBM_DAM1       0xF8   /* sector data (type 1) */
 #define IBM_DAM2       0xFB   /* sector data (type 2) */
+#define IBM_TRS80DAM1  0xF9   /* sector data (TRS-80 directory) */
+#define IBM_TRS80DAM2  0xFA   /* sector data (TRS-80 directory) */
 #define IBM_DAM_LEN    1      /* plus prologue and user data */
 
 /* Length of a DAM record is determined by the previous sector header. */