[Qemu-devel] [PATCH v4 01/11] fdc: take side count into account

[Hervé Poussineau]

Floppies can be simple or double-sided. However, current code
was only taking the common case into account (ie 2 sides).

This repairs single-sided floppies, which where totally broken
before this patch : for track > 0, wrong sector number was
calculated, and data was read/written at wrong place on
underlying device.

Fortunately, only some 360 kB floppies are single-sided, so
this bug was probably not seen much.

Signed-off-by: Hervé Poussineau <address@hidden>
---
 hw/fdc.c |   17 +++++++++++------
 1 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/hw/fdc.c b/hw/fdc.c
index f575a2c..cd479f0 100644
--- a/hw/fdc.c
+++ b/hw/fdc.c
@@ -95,16 +95,19 @@ static void fd_init(FDrive *drv)
     drv->max_track = 0;
 }
 
+#define NUM_SIDES(drv) ((drv)->flags & FDISK_DBL_SIDES ? 2 : 1)
+
 static int fd_sector_calc(uint8_t head, uint8_t track, uint8_t sect,
-                          uint8_t last_sect)
+                          uint8_t last_sect, uint8_t num_sides)
 {
-    return (((track * 2) + head) * last_sect) + sect - 1;
+    return (((track * num_sides) + head) * last_sect) + sect - 1;
 }
 
 /* Returns current position, in sectors, for given drive */
 static int fd_sector(FDrive *drv)
 {
-    return fd_sector_calc(drv->head, drv->track, drv->sect, drv->last_sect);
+    return fd_sector_calc(drv->head, drv->track, drv->sect, drv->last_sect,
+                          NUM_SIDES(drv));
 }
 
 /* Seek to a new position:
@@ -135,7 +138,7 @@ static int fd_seek(FDrive *drv, uint8_t head, uint8_t 
track, uint8_t sect,
                        drv->max_track, drv->last_sect);
         return 3;
     }
-    sector = fd_sector_calc(head, track, sect, drv->last_sect);
+    sector = fd_sector_calc(head, track, sect, drv->last_sect, NUM_SIDES(drv));
     ret = 0;
     if (sector != fd_sector(drv)) {
 #if 0
@@ -1019,7 +1022,8 @@ static void fdctrl_start_transfer(FDCtrl *fdctrl, int 
direction)
     ks = fdctrl->fifo[4];
     FLOPPY_DPRINTF("Start transfer at %d %d %02x %02x (%d)\n",
                    GET_CUR_DRV(fdctrl), kh, kt, ks,
-                   fd_sector_calc(kh, kt, ks, cur_drv->last_sect));
+                   fd_sector_calc(kh, kt, ks, cur_drv->last_sect,
+                                  NUM_SIDES(cur_drv)));
     switch (fd_seek(cur_drv, kh, kt, ks, fdctrl->config & FD_CONFIG_EIS)) {
     case 2:
         /* sect too big */
@@ -1289,7 +1293,8 @@ static void fdctrl_format_sector(FDCtrl *fdctrl)
     ks = fdctrl->fifo[8];
     FLOPPY_DPRINTF("format sector at %d %d %02x %02x (%d)\n",
                    GET_CUR_DRV(fdctrl), kh, kt, ks,
-                   fd_sector_calc(kh, kt, ks, cur_drv->last_sect));
+                   fd_sector_calc(kh, kt, ks, cur_drv->last_sect,
+                                  NUM_SIDES(cur_drv)));
     switch (fd_seek(cur_drv, kh, kt, ks, fdctrl->config & FD_CONFIG_EIS)) {
     case 2:
         /* sect too big */
-- 
1.7.8.3