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DSP: Fix the predscale update logic 

When the current address is xxxxxxxf, after doing the standard ADPCM
decoding and incrementing the current address as usual to get the
next address, the DSP will update the predscale register by reading
2 bytes from memory, and add two to get the next address.

This means xxxxxx10 cannot be a current address, as the DSP goes
from 0f to 12 directly.

A more serious issue with the old code is that if the start address
is 16-byte aligned, some samples will always be skipped, even when
that should not be the case.

An easy way to test whether this behaviour is correct is to check
the current address register and the predscale after each read.

Old code:
...
ACCA=00000002, predscale=<value>
ACCA=00000003, predscale=<value>
...
ACCA=0000000f, predscale=<value>
ACCA=00000010, predscale=<another value>
ACCA=00000013, predscale=<another value>
ACCA=00000014, predscale=<another value>
...

New code (and console):
...
ACCA=00000002, predscale=<value>
ACCA=00000003, predscale=<value>
...
ACCA=0000000f, predscale=<value>
ACCA=00000012, predscale=<another value>
ACCA=00000013, predscale=<another value>
...
This commit is contained in:
Léo Lam 2017-09-18 23:40:06 +02:00
parent 003dba5275
commit 8310a672b0
1 changed files with 7 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
Source/Core/Core/DSP/DSPAccelerator.cpp
View File

@ -73,13 +73,6 @@ u16 Accelerator::Read(s16* coefs)
{ {
case 0x00: // ADPCM audio case 0x00: // ADPCM audio
{ {
// ADPCM decoding, not much to explain here.
if ((m_current_address & 15) == 0)
{
m_pred_scale = ReadMemory((m_current_address & ~15) >> 1);
m_current_address += 2;
}
switch (m_end_address & 15) switch (m_end_address & 15)
{ {
case 0: // Tom and Jerry case 0: // Tom and Jerry
@ -111,6 +104,13 @@ u16 Accelerator::Read(s16* coefs)
m_yn2 = m_yn1; m_yn2 = m_yn1;
m_yn1 = val; m_yn1 = val;
m_current_address += 1; m_current_address += 1;
if ((m_current_address & 15) == 0)
{
m_pred_scale = ReadMemory((m_current_address & ~15) >> 1);
m_current_address += 2;
step_size_bytes += 2;
}
break; break;
} }
case 0x0A: // 16-bit PCM audio case 0x0A: // 16-bit PCM audio