[Vice-emu-commit] SF.net SVN: vice-emu: [18918] branches/marco/ports/vice/src/c64

Revision: 18918
          http://vice-emu.svn.sourceforge.net/vice-emu/?rev=18918&view=rev
Author:   blackystardust
Date:     2008-06-25 09:31:29 -0700 (Wed, 25 Jun 2008)

Log Message:
-----------
Added some more in-depth comments about the GeoRAM emulation and fixed the control registers emulation.

Modified Paths:
--------------
    branches/marco/ports/vice/src/c64/c64io.c
    branches/marco/ports/vice/src/c64/georam.c
    branches/marco/ports/vice/src/c64/georam.h

Modified: branches/marco/ports/vice/src/c64/c64io.c
===================================================================
--- branches/marco/ports/vice/src/c64/c64io.c	2008-06-24 21:30:50 UTC (rev 18917)
+++ branches/marco/ports/vice/src/c64/c64io.c	2008-06-25 16:31:29 UTC (rev 18918)
@@ -140,7 +140,7 @@
 }
 
 #define MAX_IO1_RETURNS 8
-#define MAX_IO2_RETURNS 11
+#define MAX_IO2_RETURNS 10
 
 #if MAX_IO1_RETURNS>MAX_IO2_RETURNS
 static int io_source_return[MAX_IO1_RETURNS];
@@ -409,11 +409,6 @@
         io_source_check(io_source_counter);
         io_source_counter++;
     }
-    if (georam_enabled && addr >= 0xdf80) {
-        return_value = georam_reg_read((WORD)(addr & 1));
-        io_source_check(io_source_counter);
-        io_source_counter++;
-    }
     if (mmc64_enabled && addr >= 0xdf10 && addr <= 0xdf13) {
         return_value = mmc64_io2_read((WORD)(addr));
         io_source_check(io_source_counter);

Modified: branches/marco/ports/vice/src/c64/georam.c
===================================================================
--- branches/marco/ports/vice/src/c64/georam.c	2008-06-24 21:30:50 UTC (rev 18917)
+++ branches/marco/ports/vice/src/c64/georam.c	2008-06-25 16:31:29 UTC (rev 18918)
@@ -24,6 +24,57 @@
  *
  */
 
+/*
+ * The GeoRAM is a banked memory system. It uses the registers at
+ * $dffe and $dfff to determine what part of the GeoRAM memory should
+ * be mapped to $de00-$deff.
+ *
+ * The BBG (Battery Backed GeoRAM) is a version that retains the
+ * RAM contents after power-off.
+ *
+ * The register at $dfff selects which 16k block to map, and $dffe
+ * selects a 256-byte page in that block. Since there are only 64
+ * 256-byte pages inside of 16k, the value in $dffe ranges from 0 to
+ * 63.
+ *
+ * Register | bits
+ * -------------------
+ * $dffe    | xx543210
+ *
+ * x = unused, not connected.
+ *
+ *
+ * The number of 16k blocks that is available depends on the
+ * size of the GeoRAM/BBG:
+ *
+ * RAM size | $dfff
+ * ------------------
+ *    64k   | $00-$03
+ *   128k   | $00-$07
+ *   256k   | $00-$0f
+ *   512k   | $00-$1f
+ *  1024k   | $00-$3f
+ *  2048k   | $00-$7f
+ *  2048k   | $00-$ff
+ *
+ * The unused bits in both registers are ignore and using them in
+ * software will cause a wrap-around.
+ *
+ * The two registers are write-only. Attempting to read them will
+ * only return random values.
+ *
+ * Currently both the BBG and GeoRAM are emulated, BBG mode is
+ * used when selecting a save-file.
+ *
+ * The current emulation has the two registers mirrorred through the
+ * range of $df80-$dffd
+ *
+ * There is also a user-made clone of the GeoRAM called the NeoRAM,
+ * it works in the same way as the GeoRAM but seems to have extra
+ * RAM sizes currently not supported by this emulation (like 1536k).
+ *
+ */
+
 #include "vice.h"
 
 #include <stdio.h>
@@ -294,16 +345,6 @@
 
 /* ------------------------------------------------------------------------- */
 
-BYTE REGPARM1 georam_reg_read(WORD addr)
-{
-    BYTE retval;
-
-    io_source=IO_SOURCE_GEORAM;
-    retval=georam[addr&1];
-
-    return retval;
-}
-
 BYTE REGPARM1 georam_window_read(WORD addr)
 {
     BYTE retval;

Modified: branches/marco/ports/vice/src/c64/georam.h
===================================================================
--- branches/marco/ports/vice/src/c64/georam.h	2008-06-24 21:30:50 UTC (rev 18917)
+++ branches/marco/ports/vice/src/c64/georam.h	2008-06-25 16:31:29 UTC (rev 18918)
@@ -38,7 +38,6 @@
 
 extern void georam_reset(void);
 extern void georam_shutdown(void);
-extern BYTE REGPARM1 georam_reg_read(WORD addr);
 extern BYTE REGPARM1 georam_window_read(WORD addr);
 extern void REGPARM2 georam_reg_store(WORD addr, BYTE byte);
 extern void REGPARM2 georam_window_store(WORD addr, BYTE byte);


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