PDP10: Fixed RIM loader to handle ITS and RIM10B formats

As discussed in #378

The fixes include:

1. Tightening up the "magic" code so that it can now tell EXE, SAV, and RIM
    formats apart.
2. Skipping the loader itself for both RIM10B and ITS RIM. (PDP10 Macro manual
    says that RIM10B always includes the loader.) 3. Distinguishing ITS RIM from
    RIM10B by the length of the loader block.
4. Adding the slight differences in processing between ITS RIM and RIM10B.

There is no documentation change. -R or the extension .RIM still invoke the
RIM loader, and the code tells ITS and RIM10B apart.

PDP10/pdp10_sys.c

@@ -1,6 +1,6 @@
 /* pdp10_sys.c: PDP-10 simulator interface
 
-   Copyright (c) 1993-2011, Robert M Supnik
+   Copyright (c) 1993-2017, Robert M Supnik
 
    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
@@ -23,6 +23,7 @@
    used in advertising or otherwise to promote the sale, use or other dealings
    in this Software without prior written authorization from Robert M Supnik.
 
+   20-Jan-17    RMS     Fixed RIM loader to handle ITS and RIM10B formats
    04-Apr-11    RMS     Removed DEUNA/DELUA support - never implemented
    01-Feb-07    RMS     Added CD support
    22-Jul-05    RMS     Fixed warning from Solaris C (from Doug Gwyn)
@@ -130,9 +131,9 @@ const char *sim_stop_messages[] = {
 #define EXE_PDV 01774                                   /* EXE ignored */
 #define EXE_END 01777                                   /* EXE end */
 
-/* RIM10 loader
+/* RIM10B loader
 
-   RIM10 format is a binary paper tape format (all data frames
+   RIM10B format is a binary paper tape format (all data frames
    are 200 or greater).  It consists of blocks containing
 
         -count,,origin-1
@@ -142,6 +143,30 @@ const char *sim_stop_messages[] = {
         checksum (includes IOWD)
         :
         JRST start
+
+   The checksum is the simple binary sum of all the words in
+   the block, including the IOWD.
+
+   ITS RIM format is a binary paper tape format (all data frames
+   are 200 or greater). It consists of blocks containing
+
+        -count,,origin
+        word
+        :
+        word
+        checksum (includes pseudo IOWD)
+        :
+        JRST start
+
+   The checksum is the simple binary sum of all the words in
+   the block, including the pseudo IOWD. The checksum is rotated
+   left by 1 before each new word is added in.
+
+   Both formats include the actual RIM loader as the first block.
+   It begins with a BLKI word: -count,,start-1. The count is 16(8)
+   for RIM10B and 17(8) for ITS RIM. On a real KA10 or KI10, this
+   twisty little program is loaded into the ACs and executed.
+   Here it is simply skipped.
 */
 
 d10 getrimw (FILE *fileref)
@@ -165,7 +190,25 @@ t_stat load_rim (FILE *fileref)
 {
 d10 count, cksm, data;
 a10 pa;
-int32 op;
+int32 op, i, ldrc;
+t_bool its_rim;
+extern d10 rot (d10 val, a10 ea);
+
+data = getrimw (fileref);                               /* get first word */
+if ((data < 0) || ((data & AMASK) != 0))                /* error? SA != 0? */
+    return SCPE_FMT;
+ldrc = (-((int32) LRZ (data))) & 0777777;               /* get loader count */
+if (ldrc == 016)                                        /* 16? RIM10B */
+    its_rim = FALSE;
+else if (ldrc == 017)                                   /* 17? ITS RIM */
+    its_rim = TRUE;
+else SCPE_FMT;                                          /* unknown */
+
+for (i = 0; i < ldrc; i++) {                            /* skip the loader */
+    data = getrimw (fileref);
+    if (data < 0)
+        return SCPE_FMT;
+    }
 
 for ( ;; ) {                                            /* loop until JRST */
     count = cksm = getrimw (fileref);                   /* get header */
@@ -176,14 +219,20 @@ for ( ;; ) {                                            /* loop until JRST */
             data = getrimw (fileref);                   /* get data wd */
             if (data < 0)
                 return SCPE_FMT;
-            cksm = cksm + data;                         /* add to cksm */
+            if (its_rim) {                              /* ITS RIM? */
+                cksm = (rot (cksm, 1) + data) & DMASK;  /* add to rotated cksm */
+                pa = ((a10) count) & AMASK;             /* store */
+                }
+            else {                                      /* RIM10B */
+                cksm = (cksm + data) & DMASK;           /* add to cksm */
                 pa = ((a10) count + 1) & AMASK;         /* store */
+                }
             M[pa] = data;
             }                                           /* end for */
         data = getrimw (fileref);                       /* get cksm */
         if (data < 0)
             return SCPE_FMT;
-        if ((cksm + data) & DMASK)                      /* test cksm */
+        if (cksm != data)                               /* test cksm */
             return SCPE_CSUM;
         }                                               /* end if count */
     else {
@@ -368,8 +417,11 @@ else {
         return SCPE_FMT;
     if (LRZ (data) == EXE_DIR)                          /* EXE magic? */
         fmt = FMT_E;
-    else if (TSTS (data))                               /* SAV magic? */
+    else if (TSTS (data)) {                             /* SAV/RIM magic? */
+        if ((data & AMASK) != 0)                        /* SAV has SA != 0 */
            fmt = FMT_S;
+        else fmt = FMT_R;                               /* RIM has SA == 0 */
+        }
     fseek (fileref, 0, SEEK_SET);                       /* rewind */
     }