Zack Buhman
3358d95704
The Saturn BIOS does not (un)initialize the DSP. Without zeroizing the DSP program, the SCSP DSP appears to have a program that continuously writes to 0x30000 through 0x3ffff in sound RAM, which has the effect of destroying any samples stored there.
47 lines
1.1 KiB
C++
47 lines
1.1 KiB
C++
#include <stdint.h>
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#include "smpc.h"
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#include "scsp.h"
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#include "../common/copy.hpp"
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extern void * _m68k_start __asm("_binary_m68k_interrupt_bin_start");
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extern void * _m68k_size __asm("_binary_m68k_interrupt_bin_size");
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void main()
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{
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/* SEGA SATURN TECHNICAL BULLETIN # 51
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The document suggests that Sound RAM is (somewhat) preserved
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during SNDOFF.
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*/
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while ((smpc.reg.SF & 1) != 0);
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smpc.reg.SF = 1;
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smpc.reg.COMREG = COMREG__SNDOFF;
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while (smpc.reg.oreg[31] != OREG31__SNDOFF);
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scsp.reg.ctrl.MIXER = MIXER__MEM4MB;
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reg32 * dsp_steps = reinterpret_cast<reg32*>(&(scsp.reg.dsp.STEP[0].MPRO[0]));
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fill<reg32>(dsp_steps, 0, (sizeof (scsp.reg.dsp.STEP)));
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uint32_t * m68k_main_start = reinterpret_cast<uint32_t*>(&_m68k_start);
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uint32_t m68k_main_size = reinterpret_cast<uint32_t>(&_m68k_size);
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copy<uint32_t>(&scsp.ram.u32[0], m68k_main_start, m68k_main_size);
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while ((smpc.reg.SF & 1) != 0);
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smpc.reg.SF = 1;
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smpc.reg.COMREG = COMREG__SNDON;
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while (smpc.reg.oreg[31] != OREG31__SNDON);
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// do nothing while the sound CPU manipulates the SCSP
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}
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extern "C"
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void start(void)
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{
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main();
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while (1);
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}
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