Merge pull request #545 from khokh2001/opl3_mode

opl: Add OPL3 mode.

The DMX library had limited support for the features of the OPL3 chip,
enabled by setting the DMXOPTIONS variable. This reproduces the OPL3 
support in Chocolate Doom's OPL playback and emulation layer.

Huge thanks to Alexey Khokholov for researching and developing this. 
This fixes #470.

1 files changed, 68 insertions, 14 deletions

diff --git a/opl/opl.c b/opl/opl.c
index 2800f434..a6ad4a9d 100644
--- a/opl/opl.c
+++ b/opl/opl.c
@@ -67,6 +67,8 @@ unsigned int opl_sample_rate = 22050;
 
 static int InitDriver(opl_driver_t *_driver, unsigned int port_base)
 {
+    int result1, result2;
+
     // Initialize the driver.
 
     if (!_driver->init_func(port_base))
@@ -82,7 +84,9 @@ static int InitDriver(opl_driver_t *_driver, unsigned int port_base)
     driver = _driver;
     init_stage_reg_writes = 1;
 
-    if (!OPL_Detect() || !OPL_Detect())
+    result1 = OPL_Detect();
+    result2 = OPL_Detect();
+    if (!result1 || !result2)
     {
         printf("OPL_Init: No OPL detected using '%s' driver.\n", _driver->name);
         _driver->shutdown_func();
@@ -90,15 +94,11 @@ static int InitDriver(opl_driver_t *_driver, unsigned int port_base)
         return 0;
     }
 
-    // Initialize all registers.
-
-    OPL_InitRegisters();
-
     init_stage_reg_writes = 0;
 
     printf("OPL_Init: Using driver '%s'.\n", driver->name);
 
-    return 1;
+    return result2;
 }
 
 // Find a driver automatically by trying each in the list.
@@ -106,12 +106,14 @@ static int InitDriver(opl_driver_t *_driver, unsigned int port_base)
 static int AutoSelectDriver(unsigned int port_base)
 {
     int i;
+    int result;
 
     for (i=0; drivers[i] != NULL; ++i)
     {
-        if (InitDriver(drivers[i], port_base))
+        result = InitDriver(drivers[i], port_base);
+        if (result)
         {
-            return 1;
+            return result;
         }
     }
 
@@ -127,6 +129,7 @@ int OPL_Init(unsigned int port_base)
 {
     char *driver_name;
     int i;
+    int result;
 
     driver_name = getenv("OPL_DRIVER");
 
@@ -138,9 +141,10 @@ int OPL_Init(unsigned int port_base)
         {
             if (!strcmp(driver_name, drivers[i]->name))
             {
-                if (InitDriver(drivers[i], port_base))
+                result = InitDriver(drivers[i], port_base);
+                if (result)
                 {
-                    return 1;
+                    return result;
                 }
                 else
                 {
@@ -233,7 +237,14 @@ void OPL_WriteRegister(int reg, int value)
 {
     int i;
 
-    OPL_WritePort(OPL_REGISTER_PORT, reg);
+    if (reg & 0x100)
+    {
+        OPL_WritePort(OPL_REGISTER_PORT_OPL3, reg);
+    }
+    else
+    {
+        OPL_WritePort(OPL_REGISTER_PORT, reg);
+    }
 
     // For timing, read the register port six times after writing the
     // register number to cause the appropriate delay
@@ -306,13 +317,22 @@ int OPL_Detect(void)
     // Enable interrupts:
     OPL_WriteRegister(OPL_REG_TIMER_CTRL, 0x80);
 
-    return (result1 & 0xe0) == 0x00
-        && (result2 & 0xe0) == 0xc0;
+    if ((result1 & 0xe0) == 0x00 && (result2 & 0xe0) == 0xc0)
+    {
+        result1 = OPL_ReadPort(OPL_REGISTER_PORT);
+        result2 = OPL_ReadPort(OPL_REGISTER_PORT_OPL3);
+        if (result1 == 0x00)
+        {
+            return 2;
+        }
+        return 1;
+    }
+    return 0;
 }
 
 // Initialize registers on startup
 
-void OPL_InitRegisters(void)
+void OPL_InitRegisters(int opl3)
 {
     int r;
 
@@ -349,8 +369,42 @@ void OPL_InitRegisters(void)
     // "Allow FM chips to control the waveform of each operator":
     OPL_WriteRegister(OPL_REG_WAVEFORM_ENABLE, 0x20);
 
+    if (opl3)
+    {
+        OPL_WriteRegister(OPL_REG_NEW, 0x01);
+
+        // Initialize level registers
+
+        for (r=OPL_REGS_LEVEL; r <= OPL_REGS_LEVEL + OPL_NUM_OPERATORS; ++r)
+        {
+            OPL_WriteRegister(r | 0x100, 0x3f);
+        }
+
+        // Initialize other registers
+        // These two loops write to registers that actually don't exist,
+        // but this is what Doom does ...
+        // Similarly, the <= is also intenational.
+
+        for (r=OPL_REGS_ATTACK; r <= OPL_REGS_WAVEFORM + OPL_NUM_OPERATORS; ++r)
+        {
+            OPL_WriteRegister(r | 0x100, 0x00);
+        }
+
+        // More registers ...
+
+        for (r=1; r < OPL_REGS_LEVEL; ++r)
+        {
+            OPL_WriteRegister(r | 0x100, 0x00);
+        }
+    }
+
     // Keyboard split point on (?)
     OPL_WriteRegister(OPL_REG_FM_MODE,         0x40);
+
+    if (opl3)
+    {
+        OPL_WriteRegister(OPL_REG_NEW, 0x01);
+    }
 }
 
 //