From 42fb1ed1d00c1dc0ef7de8839912aa37bd373e9e Mon Sep 17 00:00:00 2001
From: "Howard M. Harte" <hharte@magicandroidapps.com>
Date: Sun, 17 Aug 2025 14:50:44 -0700
Subject: [PATCH] AltairZ80: wd179x: Better support for 5.25-inch floppies.

---
 AltairZ80/s100_64fdc.c |  4 ++++
 AltairZ80/wd179x.c     | 40 +++++++++++++++++++++++++++++++---------
 2 files changed, 35 insertions(+), 9 deletions(-)

diff --git a/AltairZ80/s100_64fdc.c b/AltairZ80/s100_64fdc.c
index e8ca326f4..742dc4e09 100644
--- a/AltairZ80/s100_64fdc.c
+++ b/AltairZ80/s100_64fdc.c
@@ -82,6 +82,7 @@ extern t_stat set_iobase(UNIT *uptr, int32 val, CONST char *cptr, void *desc);
 extern t_stat show_iobase(FILE *st, UNIT *uptr, int32 val, CONST void *desc);
 extern uint32 sim_map_resource(uint32 baseaddr, uint32 size, uint32 resource_type,
                                int32 (*routine)(const int32, const int32, const int32), const char* name, uint8 unmap);
+void wd179x_set_rpm(int rpm);
 
 static t_stat cromfdc_svc (UNIT *uptr);
 
@@ -1586,8 +1587,10 @@ static int32 cromfdc_control(const int32 port, const int32 io, const int32 data)
         }
         if(data & CROMFDC_CTRL_MAXI) {
             wd179x_infop->drivetype = 8;
+            wd179x_set_rpm(360);
         } else {
             wd179x_infop->drivetype = 5;
+            wd179x_set_rpm(300);
         }
 
         if(data & CROMFDC_CTRL_MTRON) {
@@ -1611,6 +1614,7 @@ static int32 cromfdc_control(const int32 port, const int32 io, const int32 data)
         }
 
         sim_debug(DRIVE_MSG, &cromfdc_dev, "CROMFDC: " ADDRESS_FORMAT " WR CTRL: sel_drive=%d, drivetype=%d, motor=%d, dens=%d, aw=%d\n", PCX, wd179x_infop->sel_drive, wd179x_infop->drivetype, cromfdc_info->motor_on, wd179x_infop->ddens, cromfdc_info->autowait);
+
     } else { /* I/O Read */
         result = (crofdc_boot) ? 0 : CROMFDC_FLAG_BOOT;
         result |= (wd179x_infop->intrq) ? CROMFDC_FLAG_EOJ : 0;
diff --git a/AltairZ80/wd179x.c b/AltairZ80/wd179x.c
index 78354f853..deabf8bb5 100644
--- a/AltairZ80/wd179x.c
+++ b/AltairZ80/wd179x.c
@@ -93,11 +93,12 @@ typedef union {
 typedef struct {
     UNIT *uptr;
     DISK_INFO *imd;
-    uint8 ntracks;   /* number of tracks */
-    uint8 nheads;    /* number of heads */
-    uint32 sectsize; /* sector size, not including pre/postamble */
-    uint8 track;     /* Current Track */
-    uint8 ready;     /* Is drive ready? */
+    uint8 ntracks;      /* number of tracks */
+    uint8 nheads;       /* number of heads */
+    uint32 sectsize;    /* sector size, not including pre/postamble */
+    uint8 track;        /* Current Track */
+    uint8 ready;        /* Is drive ready? */
+    int rpm;            /* Drive RPM */
 } WD179X_DRIVE_INFO;
 
 typedef struct {
@@ -338,6 +339,14 @@ static t_stat wd179x_reset(DEVICE *dptr)
     return SCPE_OK;
 }
 
+void wd179x_set_rpm(int rpm)
+{
+    if (wd179x_info->sel_drive > WD179X_MAX_DRIVES) {
+        return;
+    }
+    wd179x_info->drive[wd179x_info->sel_drive & 3].rpm = rpm;
+}
+
 void wd179x_connect_external_fifo(uint16 fifo_len, uint8* storage)
 {
     wd179x_info->external_fifo_len = fifo_len;
@@ -1210,11 +1219,24 @@ static uint8 Do1793Command(uint8 cCommand)
                 if (cCommand & 0x04) {
                     wd179x_info->index_pulse_wait = TRUE;
                     if (wd179x_info->sel_drive < WD179X_MAX_DRIVES) {
-                        if (pDrive->uptr->u3 == IMAGE_TYPE_IMD) {
-                            sim_activate (wd179x_unit, ((wd179x_info->drive[wd179x_info->sel_drive].imd->ntracks % 77) == 0) ? CROMFDC_8IN_ROT : CROMFDC_5IN_ROT); /* Generate INDEX pulse */
-                        } else {
-                            sim_activate(wd179x_unit, CROMFDC_8IN_ROT); /* Generate INDEX pulse */
+                        int rot = 0;
+
+                        switch (pDrive->rpm) {
+                        case 300:
+                            rot = CROMFDC_5IN_ROT;
+                            break;
+                        case 360:
+                            rot = CROMFDC_8IN_ROT;
+                            break;
+                        default: /* RPM not set, infer from the disk image, if possible. */
+                            if (pDrive->uptr->u3 == IMAGE_TYPE_IMD) {
+                                rot = ((wd179x_info->drive[wd179x_info->sel_drive].imd->ntracks % 77) == 0) ? CROMFDC_8IN_ROT : CROMFDC_5IN_ROT;
+                            }
+                            else {
+                                rot = CROMFDC_8IN_ROT;
+                            }
                         }
+                        sim_activate(wd179x_unit, rot); /* Generate INDEX pulse */
                     }
                 } else {
                     wd179x_info->intrq = 1;