[Vice-emu-commit] SF.net SVN: vice-emu:[45726] trunk/vice/src

Revision: 45726
          http://sourceforge.net/p/vice-emu/code/45726
Author:   gpz
Date:     2025-08-06 18:13:36 +0000 (Wed, 06 Aug 2025)
Log Message:
-----------
add some jitter to the lsb of the POT values, partial fix for #2159

Modified Paths:
--------------
    trunk/vice/src/sid/sid.c
    trunk/vice/src/vic20/vic-mem.c

Modified: trunk/vice/src/sid/sid.c
===================================================================
--- trunk/vice/src/sid/sid.c	2025-08-06 18:10:13 UTC (rev 45725)
+++ trunk/vice/src/sid/sid.c	2025-08-06 18:13:36 UTC (rev 45726)
@@ -172,6 +172,25 @@
 #endif
 /* ------------------------------------------------------------------------- */
 
+/* Add some randomness to the pot value(s). Note that _with paddles_ the error
+   gets gradually worse depending on the sampled value (the larger the value,
+   the bigger error. This does _not_ happen with the 1351 mouse */
+static inline uint8_t makepotval(int value)
+{
+/* FIXME: we must somehow determine whether this is a 1531 or not, use the
+          lesser error for the time being */
+#if 0
+    unsigned int fuzz = lib_unsigned_rand(0, (value * 5) / 255);
+#else
+    unsigned int fuzz = lib_unsigned_rand(0, 1);
+#endif
+    value += fuzz;
+    if (value > 255) {
+        return 255;
+    }
+    return value;
+}
+
 static uint8_t sid_read_chip(uint16_t addr, int chipno)
 {
     int val = -1;
@@ -190,8 +209,8 @@
                 mouse_poll();
             }
 
-            val_pot_x = read_joyport_potx();
-            val_pot_y = read_joyport_poty();
+            val_pot_x = makepotval(read_joyport_potx());
+            val_pot_y = makepotval(read_joyport_poty());
         }
 #endif
         val = (addr == 0x19) ? val_pot_x : val_pot_y;

Modified: trunk/vice/src/vic20/vic-mem.c
===================================================================
--- trunk/vice/src/vic20/vic-mem.c	2025-08-06 18:10:13 UTC (rev 45725)
+++ trunk/vice/src/vic20/vic-mem.c	2025-08-06 18:13:36 UTC (rev 45726)
@@ -33,6 +33,7 @@
 #include <string.h>
 
 #include "joyport.h"
+#include "lib.h"
 #include "maincpu.h"
 #include "raster-changes.h"
 #include "types.h"
@@ -285,6 +286,25 @@
     return ypos;
 }
 
+/* Add some randomness to the pot value(s). Note that _with paddles_ the error
+   gets gradually worse depending on the sampled value (the larger the value,
+   the bigger error. This does _not_ happen with the 1351 mouse */
+static inline uint8_t makepotval(int value)
+{
+/* FIXME: we must somehow determine whether this is a 1531 or not, use the
+          lesser error for the time being */
+#if 0
+    unsigned int fuzz = lib_unsigned_rand(0, (value * 5) / 255);
+#else
+    unsigned int fuzz = lib_unsigned_rand(0, 1);
+#endif
+    value += fuzz;
+    if (value > 255) {
+        return 255;
+    }
+    return value;
+}
+
 uint8_t vic_read(uint16_t addr)
 {
     addr &= 0xf;
@@ -298,8 +318,8 @@
                 mouse_poll();
             }
 
-            vic.regs[8] = read_joyport_potx();
-            vic.regs[9] = read_joyport_poty();
+            vic.regs[8] = makepotval(read_joyport_potx());
+            vic.regs[9] = makepotval(read_joyport_poty());
         }
     }
 #endif

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