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Improve ReadD3 emulation

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xperia64 2022-06-10 21:38:26 -04:00 • committed by Tillmann Karras
parent 05124b29be
commit 80a0428116
1 changed files with 48 additions and 7 deletions
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55
Source/Core/Core/DSP/DSPAccelerator.cpp
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@ -15,26 +15,67 @@ u16 Accelerator::ReadD3()
{
u16 val = 0;
switch (m_sample_format)
// The lower two bits of the sample format indicate the access size
switch (m_sample_format & 3)
{
case 0x5: // u8 reads
case 0x0: // u4 reads
val = ReadMemory(m_current_address / 2);
if (m_current_address & 1)
val &= 0xf;
else
val >>= 4;
m_current_address++;
break;
case 0x1: // u8 reads
val = ReadMemory(m_current_address);
m_current_address++;
break;
case 0x6: // u16 reads
case 0x2: // u16 reads
val = (ReadMemory(m_current_address * 2) << 8) | ReadMemory(m_current_address * 2 + 1);
m_current_address++;
break;
default:
ERROR_LOG_FMT(DSPLLE, "dsp_read_aram_d3() - unknown format {:#x}", m_sample_format);
case 0x3: // produces garbage, but affects the current address
ERROR_LOG_FMT(DSPLLE, "dsp_read_aram_d3() - bad format {:#x}", m_sample_format);
m_current_address = (m_current_address & ~3) | ((m_current_address + 1) & 3);
break;
}
if (m_current_address >= m_end_address)
// There are edge cases that are currently not handled here in u4 and u8 mode
// In u8 mode, if ea & 1 == 0 and ca == ea + 1, the accelerator can be read twice. Upon the second
// read, the data returned appears to be the other half of the u16 from the first read, and the
// DSP resets the current address and throws exception 3
// During these reads, ca is not incremented normally.
// Instead, incrementing ca works like this: ca = (ca & ~ 3) | ((ca + 1) & 3)
// u4 mode extends this further.
// When ea & 3 == 0, and ca in [ea + 1, ea + 3], the accelerator can be read (4 - (ca - ea - 1))
// times. On the last read, the data returned appears to be the remaining nibble of the u16 from
// the first read, and the DSP resets the current address and throws exception 3
// When ea & 3 == 1, and ca in [ea + 1, ea + 2], the accelerator can be read (4 - (ca - ea - 1))
// times. On the last read, the data returned appears to be the remaining nibble of the u16 from
// the first read, and the DSP resets the current address and throws exception 3
// When ea & 3 == 2, and ca == ea + 1, the accelerator can be read 4 times. On the last read, the
// data returned appears to be the remaining nibble of the u16 from the first read, and the DSP
// resets the current address and throws exception 3
// There are extra extra edge cases if ca, ea, and potentially other registers are adjusted during
// this pre-reset phase
// The cleanest way to emulate the normal non-edge behavior is to only reset things if we just
// read the end address If the current address is larger than the end address (and not in the edge
// range), it ignores the end address
if (m_current_address - 1 == m_end_address)
{
// Set address back to start address. (never seen this here!)
// Set address back to start address (confirmed on hardware)
m_current_address = m_start_address;
OnEndException();
}
SetCurrentAddress(m_current_address);
return val;
}