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Read from register port when doing register writes during startup phase;
afterwards, read from the data port.

Subversion-branch: /branches/opl-branch
Subversion-revision: 1464

--- a/src/i_oplmusic.c

+++ b/src/i_oplmusic.c

@@ -116,6 +116,13 @@

 static opl_voice_t voices[OPL_NUM_VOICES];

 static opl_voice_t *voice_free_list;

+// In the initialisation stage, register writes are spaced by reading

+// from the register port (0).  After initialisation, spacing is

+// peformed by reading from the data port instead.  I have no idea

+// why.

+

+static boolean init_stage_reg_writes = false;

+

 // Configuration file variable, containing the port number for the

 // adlib chip.

@@ -139,7 +146,18 @@

     for (i=0; i<6; ++i)

     {

-        GetStatus();

+        // An oddity of the Doom OPL code: at startup initialisation,

+        // the spacing here is performed by reading from the register

+        // port; after initialisation, the data port is read, instead.

+

+        if (init_stage_reg_writes)

+        {

+            OPL_ReadPort(OPL_REGISTER_PORT);

+        }

+        else

+        {

+            OPL_ReadPort(OPL_DATA_PORT);

+        }

     }

     OPL_WritePort(OPL_DATA_PORT, value);

@@ -393,6 +411,8 @@

         return false;

     }

+    init_stage_reg_writes = true;

+

     // Doom does the detection sequence twice, for some reason:

     if (!DetectOPL() || !DetectOPL())

@@ -412,6 +432,11 @@

     InitRegisters();

     InitVoices();

+

+    // Now that initialisation has finished, switch the

+    // register writing mode:

+

+    init_stage_reg_writes = false;

 #ifdef TEST

     {