Give the disk four drives, behind one controller

SEVERAL DISKS ARE ONE CONTROLLER AND NOT SEVERAL DEVICES, and the
instruction set decided that rather than taste. A port is an immediate byte
inside the OUT that names it - portOut takes it from Program Memory - so a
program cannot compute one. "The disk on port 0x20 plus drive times four"
is not something this machine can say, and two disks as two devices would
mean a branch on the drive number in all eleven places sbfs.asm names a
disk port. A drive register is what a floppy controller has always been.

  0x24  Drive, which the block, command and status registers refer to
  0x25  Drives, read only: how many are plugged in

--disk given more than once fills them in order. What is per drive is the
image, its size and its write protection; the block register, the status
and the one buffer belong to the controller, which is the same division
real hardware makes.

A drive that is not there is refused rather than wrapped, because wrapping
means a program asking for a drive this machine has not got quietly reading
the one it has - the same shape of fault as taking a bank number somebody
else was using. An EMPTY drive is a different thing and is selectable: a
controller has its drives whether or not there are disks in them, and
reading one fails with the error bit the way an empty drive should.

Changing drives finishes whatever the one being left was in the middle of.
A transfer waits for the clock, so one may be owed at any moment, and
running it against the disk that is arriving would be a fault with no
owner.

Also stops parseOptions setting its defaults field by field. It was nine
assignments beside a struct, and a list beside a thing drifts from the
thing: adding two fields left them holding whatever was on the stack, so a
machine given one disk was told it already had four drives. It is one
zeroing now, and a default that is not nought can be written under it where
it reads as the exception. That struct growing a field once before left
Voyager linked against an object that disagreed about its size.

Nothing in CosmOS uses any of this yet. The mount record is next.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW

Source/Emulator/utility.c

@@ -57,15 +57,17 @@ uint8_t parseOptions(int argc, char *argv[], EmulatorOptions *options) {
         int opt;
         int option_index = 0;
 
-    options->debug = 0;
-    options->fast = 0;
-    options->cycles = 0;
-    options->disk = NULL;
-    options->writeProtect = 0;
-    options->diskCycles = 0;
-    options->screen = NULL;
-    options->keyboard = NULL;
-    options->sound = NULL;
+    // ---- Everything off, in one line rather than nine ----
+    //
+    // This was a list of assignments, one per field, and a list beside a struct drifts from
+    // the struct: adding `disks` and `diskCount` left them holding whatever was on the stack,
+    // so a machine given one disk was told it already had four drives. The same struct
+    // growing a field once before left Voyager linking against an object that disagreed
+    // about its size.
+    //
+    // Every default here is nought or nothing, and a default that is not can be written
+    // below this line where it will be read as the exception it is.
+    *options = (EmulatorOptions){0};
 
     // Parse options
     while ((opt = getopt_long(argc, argv, "dc:fhD:WL:S:K:N:", long_options, &option_index)) != -1) {
@@ -90,7 +92,18 @@ uint8_t parseOptions(int argc, char *argv[], EmulatorOptions *options) {
                 options->fast = 1;
             break;
             case 'D':
-                options->disk = optarg;
+                // Each one is the next drive. The first is also left in `disk`, because a
+                // machine with one disk is what almost every caller means and reading it
+                // that way keeps them all unchanged.
+                if (options->diskCount >= DISK_DRIVE_COUNT) {
+                    fprintf(stderr, "Error: This machine has %d drives.\n",
+                            DISK_DRIVE_COUNT);
+                    return 1;
+                }
+                options->disks[options->diskCount++] = optarg;
+                if (options->disk == NULL) {
+                    options->disk = optarg;
+                }
             break;
             case 'W':
                 options->writeProtect = 1;