X-Git-Url: http://shamusworld.gotdns.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fdac.cpp;h=983680791fccefe73613246120633f4bf8543e95;hb=19cb30261693d5c56c79d87030cfe8e1dc9ca033;hp=dbb1b5842caeef2469dce21d0c46589391a4f259;hpb=bae593a9f2f6557d271d8b2eacc5d4a825cf4b0a;p=virtualjaguar

diff --git a/src/dac.cpp b/src/dac.cpp
index dbb1b58..9836807 100644
--- a/src/dac.cpp
+++ b/src/dac.cpp
@@ -3,10 +3,10 @@
 //
 // Originally by David Raingeard
 // GCC/SDL port by Niels Wagenaar (Linux/WIN32) and Caz (BeOS)
-// Rewritten by James L. Hammons
+// Rewritten by James Hammons
 // (C) 2010 Underground Software
 //
-// JLH = James L. Hammons <jlhamm@acm.org>
+// JLH = James Hammons <jlhamm@acm.org>
 //
 // Who  When        What
 // ---  ----------  -------------------------------------------------------------
@@ -26,6 +26,27 @@
 //       to prevent things like the DSP filling only one side and such. Do such
 //       mono modes exist on the Jag? Seems to according to Super Burnout.
 
+// After testing on a real Jaguar, it seems clear that the I2S interrupt drives
+// the audio subsystem. So while you can drive the audio at a *slower* rate than
+// set by SCLK, you can't drive it any *faster*. Also note, that if the I2S
+// interrupt is not enabled/running on the DSP, then there is no audio. Also,
+// audio can be muted by clearing bit 8 of JOYSTICK (JOY1).
+//
+// Approach: We can run the DSP in the host system's audio IRQ, by running the
+// DSP for the alloted time (depending on the host buffer size & sample rate)
+// by simply reading the L/R_I2S (L/RTXD) registers at regular intervals. We
+// would also have to time the I2S/TIMER0/TIMER1 interrupts in the DSP as well.
+// This way, we can run the host audio IRQ at, say, 48 KHz and not have to care
+// so much about SCLK and running a separate buffer and all the attendant
+// garbage that comes with that awful approach.
+//
+// There would still be potential gotchas, as the SCLK can theoretically drive
+// the I2S at 26590906 / 2 (for SCLK == 0) = 13.3 MHz which corresponds to an
+// audio rate 416 KHz (dividing the I2S rate by 32, for 16-bit stereo). It
+// seems doubtful that anything useful could come of such a high rate, and we
+// can probably safely ignore any such ridiculously high audio rates. It won't
+// sound the same as on a real Jaguar, but who cares? :-)
+
 #include "dac.h"
 
 #include "SDL.h"
@@ -69,7 +90,6 @@ static uint8 SCLKFrequencyDivider = 19;				// Default is roughly 22 KHz (20774 H
 // Private function prototypes
 
 void SDLSoundCallback(void * userdata, Uint8 * buffer, int length);
-int GetCalculatedFrequency(void);
 
 //
 // Initialize the SDL sound system
@@ -128,6 +148,16 @@ void DACDone(void)
 	WriteLog("DAC: Done.\n");
 }
 
+
+// Approach: Run the DSP for however many cycles needed to correspond to whatever sample rate
+// we've set the audio to run at. So, e.g., if we run it at 48 KHz, then we would run the DSP
+// for however much time it takes to fill the buffer. So with a 2K buffer, this would correspond
+// to running the DSP for 0.042666... seconds. At 26590906 Hz, this would correspond to
+// running the DSP for 1134545 cycles. You would then sample the L/RTXD registers every
+// 1134545 / 2048 = 554 cycles to fill the buffer. You would also have to manage interrupt
+// timing as well (generating them at the proper times), but that shouldn't be too difficult...
+// If the DSP isn't running, then fill the buffer with L/RTXD and exit.
+
 //
 // SDL callback routine to fill audio buffer
 //
@@ -201,6 +231,44 @@ int GetCalculatedFrequency(void)
 	return systemClockFrequency / (32 * (2 * (SCLKFrequencyDivider + 1)));
 }
 
+static int oldFreq = 0;
+
+void DACSetNewFrequency(int freq)
+{
+	if (freq == oldFreq)
+		return;
+
+	oldFreq = freq;
+
+	// Should do some sanity checking on the frequency...
+
+	if (SDLSoundInitialized)
+		SDL_CloseAudio();
+
+	desired.freq = freq;// SDL will do conversion on the fly, if it can't get the exact rate. Nice!
+	WriteLog("DAC: Changing sample rate to %u Hz!\n", desired.freq);
+
+	if (SDLSoundInitialized)
+	{
+		if (SDL_OpenAudio(&desired, NULL) < 0)	// NULL means SDL guarantees what we want
+		{
+// This is bad, Bad, BAD !!! DON'T ABORT BECAUSE WE DIDN'T GET OUR FREQ! !!! FIX !!!
+#warning !!! FIX !!! Aborting because of SDL audio problem is bad!
+			WriteLog("DAC: Failed to initialize SDL sound: %s.\nDesired freq: %u\nShutting down!\n", SDL_GetError(), desired.freq);
+//						LogDone();
+//						exit(1);
+#warning "Reimplement GUICrashGracefully!"
+//						GUICrashGracefully("Failed to initialize SDL sound!");
+			return;
+		}
+	}
+
+	DACReset();
+
+	if (SDLSoundInitialized)
+		SDL_PauseAudio(false);			// Start playback!
+}
+
 //
 // LTXD/RTXD/SCLK/SMODE ($F1A148/4C/50/54)
 //