From 6c84387ec005e0b77644aaa8ca9a2b9e3e371582 Mon Sep 17 00:00:00 2001
From: Peter Schorn <peter.schorn@acm.org>
Date: Tue, 18 Feb 2020 11:55:29 +0100
Subject: [PATCH] AltairZ80: Fix error handling of bad IMD disks and sector
 size computation

---
 AltairZ80/altairz80_hdsk.c | 4 +++-
 sim_imd.c                  | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/AltairZ80/altairz80_hdsk.c b/AltairZ80/altairz80_hdsk.c
index fd96c543..9a2f449b 100644
--- a/AltairZ80/altairz80_hdsk.c
+++ b/AltairZ80/altairz80_hdsk.c
@@ -449,8 +449,10 @@ static t_stat hdsk_attach(UNIT *uptr, CONST char *cptr) {
         hdsk_imd[thisUnitIndex] = diskOpenEx(uptr -> fileref,
                                              sim_deb && (hdsk_dev.dctrl & VERBOSE_MSG),
                                              &hdsk_dev, VERBOSE_MSG, VERBOSE_MSG);
-        if (hdsk_imd[thisUnitIndex] == NULL)
+        if (hdsk_imd[thisUnitIndex] == NULL) {
+            detach_unit(uptr);
             return SCPE_IOERR;
+        }
         verifyDiskInfo(hdsk_imd[thisUnitIndex], '0' + thisUnitIndex);
         uptr -> HDSK_NUMBER_OF_TRACKS = hdsk_imd[thisUnitIndex] -> ntracks;
         uptr -> HDSK_SECTORS_PER_TRACK = hdsk_imd[thisUnitIndex] -> track[1][0].nsects;
diff --git a/sim_imd.c b/sim_imd.c
index b1d09499..fab8f6af 100644
--- a/sim_imd.c
+++ b/sim_imd.c
@@ -164,7 +164,7 @@ static t_stat diskParse(DISK_INFO *myDisk, uint32 isVerbose)
         sim_fread(&imd, 1, 5, myDisk->file);
         if (feof(myDisk->file))
             break;
-        sectorSize = 128 << imd.sectsize;
+        sectorSize = 128 << (imd.sectsize & 0x1f);
         sectorHeadwithFlags = imd.head; /*AGN save the head and flags */
         imd.head &= 1 ; /*AGN mask out flag bits to head 0 or 1 */