Merge pull request #95 from Provenance-Emu/libretro/feature/counter-accuracy

Improve counter/timer accuracy (HC, JERRY PITs)

Author: JoeMatt

libretro.c

@@ -347,11 +347,17 @@ static void check_variables(void)
 
    for (i = 0; i < 2; i++)
    {
+      int j;
       char base[20];
       char key[64];
       size_t _len        = strlcpy(base, "virtualjaguar_p", sizeof(base));
       snprintf(base + _len, sizeof(base) - _len, "%d", i + 1);
 
+      /* Initialize all retropad mappings to BUTTON_NONE so unmapped
+       * entries don't accidentally trigger BUTTON_U (index 0). */
+      for (j = 0; j < 24; j++)
+         jag_retropad[i][j] = BUTTON_NONE;
+
       strlcpy(key, base, sizeof(key));
       strlcat(key, "_numpad_to_kb", sizeof(key));
       var.key   = key;

src/dsp.c

@@ -822,7 +822,7 @@ void DSPReset(void)
 
 	// Contents of local RAM are quasi-stable; we simulate this by randomizing RAM contents
 	for(i=0; i<8192; i+=4)
-		*((uint32_t *)(&dsp_ram_8[i])) = rand();
+		*((uint32_t *)(&dsp_ram_8[i])) = JaguarRand();
 }
 
 void DSPDone(void)

src/gpu.c

@@ -666,7 +666,7 @@ void GPUReset(void)
 
    // Contents of local RAM are quasi-stable; we simulate this by randomizing RAM contents
    for(i=0; i<4096; i+=4)
-      *((uint32_t *)(&gpu_ram_8[i])) = rand();
+      *((uint32_t *)(&gpu_ram_8[i])) = JaguarRand();
 }
 
 uint32_t GPUReadPC(void)

src/jaguar.c

@@ -16,8 +16,6 @@
 #include <string.h>
 #include <stdlib.h>
 
-#include <time.h>
-
 #include "jaguar.h"
 
 #include "cdrom.h"
@@ -35,6 +33,24 @@
 
 static bool frameDone;
 
+// Platform-independent xorshift32 PRNG for deterministic RAM initialization.
+// libc rand() produces different sequences on different platforms (glibc vs
+// macOS libsystem), which causes cross-platform baseline mismatches.
+static uint32_t jaguar_prng_state = 12345;
+
+void JaguarSeedPRNG(uint32_t seed)
+{
+   jaguar_prng_state = seed ? seed : 1;
+}
+
+uint32_t JaguarRand(void)
+{
+   jaguar_prng_state ^= jaguar_prng_state << 13;
+   jaguar_prng_state ^= jaguar_prng_state >> 17;
+   jaguar_prng_state ^= jaguar_prng_state << 5;
+   return jaguar_prng_state;
+}
+
 #define ALPINE_FUNCTIONS
 
 // Private function prototypes
@@ -541,12 +557,12 @@ void JaguarSetScreenPitch(uint32_t pitch)
 void JaguarInit(void)
 {
    unsigned i;
-   // For randomizing RAM
-   srand(time(NULL));
+   // Reset the platform-independent PRNG for deterministic RAM fill
+   JaguarSeedPRNG(12345);
 
    // Contents of local RAM are quasi-stable; we simulate this by randomizing RAM contents
    for(i=0; i<0x200000; i+=4)
-      *((uint32_t *)(&jaguarMainRAM[i])) = rand();
+      *((uint32_t *)(&jaguarMainRAM[i])) = JaguarRand();
 
    lowerField = false;							// Reset the lower field flag
    memset(jaguarMainRAM + 0x804, 0xFF, 4);
@@ -631,8 +647,9 @@ void JaguarReset(void)
 
    // Only problem with this approach: It wipes out RAM loaded files...!
    // Contents of local RAM are quasi-stable; we simulate this by randomizing RAM contents
+   JaguarSeedPRNG(12345);
    for(i=8; i<0x200000; i+=4)
-      *((uint32_t *)(&jaguarMainRAM[i])) = rand();
+      *((uint32_t *)(&jaguarMainRAM[i])) = JaguarRand();
 
    // New timer base code stuffola...
    InitializeEventList();

src/jaguar.h

@@ -16,6 +16,8 @@ void JaguarSetScreenPitch(uint32_t pitch);
 void JaguarInit(void);
 void JaguarReset(void);
 void JaguarDone(void);
+void JaguarSeedPRNG(uint32_t seed);
+uint32_t JaguarRand(void);
 
 uint8_t JaguarReadByte(uint32_t offset, uint32_t who);
 uint16_t JaguarReadWord(uint32_t offset, uint32_t who);

src/jerry.c

@@ -386,7 +386,18 @@ uint8_t JERRYReadByte(uint32_t offset, uint32_t who/*=UNKNOWN*/)
    //	F1003C          R     xxxxxxxx xxxxxxxx   JPIT4 - timer 2 divider
    else if ((offset >= 0xF10036) && (offset <= 0xF1003D))
    {
-      /* Unhandled timer read (BYTE) */
+      uint16_t value;
+
+      switch (offset & 0xFFFFFFFE)
+      {
+         case 0xF10036: value = JERRYPIT1Prescaler; break;
+         case 0xF10038: value = JERRYPIT1Divider;   break;
+         case 0xF1003A: value = JERRYPIT2Prescaler; break;
+         case 0xF1003C: value = JERRYPIT2Divider;   break;
+         default:       value = 0;                  break;
+      }
+
+      return (offset & 0x01) ? (value & 0xFF) : (value >> 8);
    }
    else if (offset >= 0xF14000 && offset <= 0xF14003)
    {
@@ -426,7 +437,14 @@ uint16_t JERRYReadWord(uint32_t offset, uint32_t who/*=UNKNOWN*/)
    //	F1003C          R     xxxxxxxx xxxxxxxx   JPIT4 - timer 2 divider
    else if ((offset >= 0xF10036) && (offset <= 0xF1003D))
    {
-      /* Unhandled timer read (WORD) */
+      switch (offset & 0xFFFFFFFE)
+      {
+         case 0xF10036: return JERRYPIT1Prescaler;
+         case 0xF10038: return JERRYPIT1Divider;
+         case 0xF1003A: return JERRYPIT2Prescaler;
+         case 0xF1003C: return JERRYPIT2Divider;
+         default:       return 0;
+      }
    }
    else if (offset == 0xF10020)
       return jerryPendingInterrupt;

src/tom.c

@@ -256,7 +256,6 @@
 #include "tom.h"
 
 #include <string.h>								// For memset()
-#include <stdlib.h>								// For rand()
 #include "blitter.h"
 #include "event.h"
 #include "gpu.h"
@@ -732,9 +731,19 @@ void TOMExecHalfline(uint16_t halfline, bool render)
    uint32_t * TOMCurrentLine = 0;
    uint16_t topVisible;
    uint16_t bottomVisible;
+   uint16_t hp = GET16(tomRam8, HP);
 
    halfline &= 0x07FF;
 
+   // Update HC to approximate position within the scanline.
+   // Bit 10 (0x0400) is the half-line indicator, analogous to VC's
+   // field bit 11. The OP tests this via CONDITION_SECOND_HALF_LINE.
+   // Bits 0-9 approximate the position within the half-line.
+   if (halfline & 0x01)
+      SET16(tomRam8, HC, 0x0400 | (hp > 0 ? (hp + 1) / 2 : 0));
+   else
+      SET16(tomRam8, HC, 0);
+
    if (halfline & 0x01)							// Execute OP only on even halflines (non-interlaced only!)
       // Execute OP only on even halflines (skip higher resolutions for now...)
       return;
@@ -919,7 +928,8 @@ uint16_t TOMReadWord(uint32_t offset, uint32_t who)
       return data;
    }
    else if (offset == 0xF00004)
-      return rand() & 0x03FF;
+      // Return the current HC value from tomRam8 (updated each halfline)
+      return GET16(tomRam8, HC);
    else if ((offset >= GPU_CONTROL_RAM_BASE) && (offset < GPU_CONTROL_RAM_BASE + 0x20))
       return GPUReadWord(offset, who);
    else if ((offset >= GPU_WORK_RAM_BASE) && (offset < GPU_WORK_RAM_BASE + 0x1000))