From f62037ad64341fa37e2bba9a42acac9b09594ada Mon Sep 17 00:00:00 2001
From: Ian C <ianc@noddybox.co.uk>
Date: Tue, 10 Jan 2023 17:34:06 +0000
Subject: Changed ROM patches.  Attempts to fix TAP loading.  Still balking at
 bad files.

---
 source/snap.c | 45 +++++++++++++++++++++++++++++----------------
 1 file changed, 29 insertions(+), 16 deletions(-)

(limited to 'source/snap.c')

diff --git a/source/snap.c b/source/snap.c
index 3ef3690..789d7d5 100644
--- a/source/snap.c
+++ b/source/snap.c
@@ -101,16 +101,17 @@ int TAPLoad(Z80Byte id, Z80Word *addr, Z80Word *len, SNAP_Poke poke)
     Z80Word blen;
     Z80Byte type,b,csum,tape_csum;
 
-    if (!tapfile)
-    {
-    	return FALSE;
-    }
-
     b = 0;
 
     blen = GetTAPLSBWord();
     type = GetTAPByte();
-    csum = id;
+    csum = type;
+
+    if (!tapfile)
+    {
+        SPEC_DEBUG("Tape not open, returning FALSE\n");
+    	return FALSE;
+    }
 
     SPEC_DEBUG("Read block.  len=%u type=%u\n", (unsigned)blen, (unsigned)type);
     SPEC_DEBUG("Requested block len=%u type=%u addr=%u\n",
@@ -142,28 +143,40 @@ int TAPLoad(Z80Byte id, Z80Word *addr, Z80Word *len, SNAP_Poke poke)
         SPEC_DEBUG("Finished block.  Remaining blen=%u len=%u\n",
                                 (unsigned)blen, (unsigned)*len);
 
-	/* Get the checksum
+	/* Get the checksum.  If the length was correct there should be just
+           byte left in blen, but decrement it in a loop to skip to the end.
 	*/
 	if (blen)
 	{
-	    tape_csum=GetTAPByte();
-	    blen--;
+            while(blen--)
+            {
+                tape_csum=GetTAPByte();
+
+                if (blen)
+                {
+                    csum ^= tape_csum;
+                }
+            }
 	}
 	else
         {
 	    tape_csum=b;
         }
 
-	/* In case we've been request less bytes than the block size
+	/* Check the checksum
 	*/
-	while(blen--)
+        if (csum == tape_csum)
         {
-	    GetTAPByte();
+            SPEC_DEBUG("Checksum %u (calc) and %u (tape) match\n",
+                                (unsigned)csum, (unsigned)tape_csum);
+            return TRUE;
+        }
+        else
+        {
+            SPEC_DEBUG("Checksum %u (calc) and %u (tape) DON'T match\n",
+                                (unsigned)csum, (unsigned)tape_csum);
+            return FALSE;
         }
-
-	/* Check the checksum
-	*/
-	return csum == tape_csum;
     }
     else
     {
-- 
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