SDS: Added C register implementation for various devices

SDS/sds_rad.c

@@ -1,6 +1,6 @@
 /* sds_rad.c: SDS 940 fixed head disk simulator
 
-   Copyright (c) 2001-2008, Robert M. Supnik
+   Copyright (c) 2001-2021, 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"),
@@ -25,6 +25,8 @@
 
    rad          fixed head disk
 
+   17-Feb-21    kenr    Added C register support to RAD boot
+
    The fixed head disk is a head-per-track disk, with up to four disks.  Each
    disk is divided into two logical units.  Reads and writes cannot cross logical
    unit boundaries.  The fixed head disk transfers 12b characters, rather than 6b
@@ -326,7 +328,7 @@ return SCPE_OK;
 
 t_stat rad_boot (int32 unitno, DEVICE *dptr)
 {
-extern uint32 P, M[];
+extern uint32 P, C, M[];
 
 if (unitno)                                             /* only unit 0 */
     return SCPE_ARG;
@@ -338,5 +340,6 @@ M[2] = 000203226;                                       /* EOM 3226B */
 M[3] = 003200002;                                       /* WIM 2 */
 M[4] = 000100002;                                       /* BRU 2 */
 P = 1;                                                  /* start at 1 */
+C = M[1];
 return SCPE_OK;
 }