Improve counter/timer accuracy (TOM HC, JERRY PIT reads)

- Replace rand() stub for TOM Horizontal Count (HC) register with
  deterministic halfline-based approximation. HC is now updated in
  TOMExecHalfline() to 0 at even halflines and HP/2 at odd halflines.
  This fixes non-deterministic behavior and gives the Object Processor's
  CONDITION_SECOND_HALF_LINE branch a meaningful value.

- Implement JERRY timer register reads (JPIT1-JPIT4 at F10036-F1003D).
  Both byte and word reads now return the current prescaler/divider
  values instead of silently returning 0.

Refs #62

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Author: JoeMatt

src/jerry.c

@@ -384,9 +384,24 @@ uint8_t JERRYReadByte(uint32_t offset, uint32_t who/*=UNKNOWN*/)
    //	F10038          R     xxxxxxxx xxxxxxxx   JPIT2 - timer 1 divider
    //	F1003A          R     xxxxxxxx xxxxxxxx   JPIT3 - timer 2 pre-scaler
    //	F1003C          R     xxxxxxxx xxxxxxxx   JPIT4 - timer 2 divider
+   //	F10036          R     xxxxxxxx xxxxxxxx   JPIT1 - timer 1 pre-scaler
+   //	F10038          R     xxxxxxxx xxxxxxxx   JPIT2 - timer 1 divider
+   //	F1003A          R     xxxxxxxx xxxxxxxx   JPIT3 - timer 2 pre-scaler
+   //	F1003C          R     xxxxxxxx xxxxxxxx   JPIT4 - timer 2 divider
    else if ((offset >= 0xF10036) && (offset <= 0xF1003D))
    {
-      /* Unhandled timer read (BYTE) */
+      uint16_t value;
+
+      switch (offset & 0xFE)
+      {
+         case 0x36: value = JERRYPIT1Prescaler; break;
+         case 0x38: value = JERRYPIT1Divider;   break;
+         case 0x3A: value = JERRYPIT2Prescaler; break;
+         case 0x3C: value = JERRYPIT2Divider;   break;
+         default:   value = 0;                  break;
+      }
+
+      return (offset & 0x01) ? (value & 0xFF) : (value >> 8);
    }
    else if (offset >= 0xF14000 && offset <= 0xF14003)
    {
@@ -426,7 +441,13 @@ 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)
+      {
+         case 0xF10036: return JERRYPIT1Prescaler;
+         case 0xF10038: return JERRYPIT1Divider;
+         case 0xF1003A: return JERRYPIT2Prescaler;
+         case 0xF1003C: return JERRYPIT2Divider;
+      }
    }
    else if (offset == 0xF10020)
       return jerryPendingInterrupt;

src/tom.c

@@ -732,9 +732,20 @@ 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.
+   // Even halflines = start of scanline (HC near 0),
+   // odd halflines = midpoint of scanline (HC near HP/2).
+   // This is not cycle-accurate but gives the OP and games a
+   // meaningful value instead of the previous rand() stub.
+   if (halfline & 0x01)
+      SET16(tomRam8, HC, (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 +930,8 @@ 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))