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CDROM: Use physical position for seek time calculations

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This commit is contained in:
Connor McLaughlin 2021-06-12 17:39:54 +10:00
parent 36bfc461f9
commit 74013a0853
2 changed files with 26 additions and 17 deletions
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38
src/core/cdrom.cpp
View file

@ -699,15 +699,13 @@ TickCount CDROM::GetTicksForSeek(CDImage::LBA new_lba)
if (g_settings.cdrom_seek_speedup == 0)
return MIN_TICKS;
UpdatePhysicalPosition();
const TickCount tps = System::GetTicksPerSecond();
const CDImage::LBA current_lba = m_secondary_status.motor_on ? m_current_lba : 0;
const CDImage::LBA current_lba = m_secondary_status.motor_on ? m_physical_lba : 0;
const u32 lba_diff = static_cast<u32>((new_lba > current_lba) ? (new_lba - current_lba) : (current_lba - new_lba));
// Original formula based on Mednafen. Still not accurate, doesn't consider the varying number of sectors per track.
// TODO: Replace with algorithm based on mechacon behavior.
u32 ticks = std::max<u32>(
20000, static_cast<u32>(
((static_cast<u64>(lba_diff) * static_cast<u64>(tps) * static_cast<u64>(1000)) / (72 * 60 * 75)) / 1000));
u32 ticks = static_cast<u32>(MIN_TICKS);
// Motor spin-up time.
if (!m_secondary_status.motor_on)
@ -718,14 +716,24 @@ TickCount CDROM::GetTicksForSeek(CDImage::LBA new_lba)
ClearDriveState();
}
if (lba_diff >= 2550)
ticks += static_cast<u32>((u64(tps) * 300) / 1000);
if (lba_diff < 32)
{
ticks += static_cast<u32>(GetTicksForRead()) * std::min<u32>(BASE_SECTORS_PER_TRACK, lba_diff);
}
else
{
// When paused, the CDC seems to keep reading the disc until it hits the position it's set to, then skip 10-15
// sectors back (depending on how far into the disc it is). We'll be generous and use 4 sectors, since on average
// it's probably closer.
ticks += static_cast<u32>(GetTicksForRead()) * 4u;
// This is a very inaccurate model.
// TODO: Use the actual time for track jumps.
// 1000ms for the whole disc
ticks += std::max<u32>(
20000,
static_cast<u32>(
((static_cast<u64>(lba_diff) * static_cast<u64>(tps) * static_cast<u64>(1000)) / (72 * 60 * 75)) / 1000));
// 300ms for non-short seeks
if (lba_diff >= 2550)
ticks += static_cast<u32>((u64(tps) * 300) / 1000);
}
if (m_mode.double_speed != m_current_double_speed)
@ -1741,19 +1749,17 @@ void CDROM::UpdatePhysicalPosition()
return;
}
const CDImage::LBA SECTORS_TO_JUMP_BACK = 9;
const u32 diff = ticks - m_physical_lba_update_tick;
const u32 sector_diff = diff / GetTicksForRead();
if (sector_diff > 0)
{
const CDImage::LBA base =
(m_current_lba >= SECTORS_TO_JUMP_BACK) ? (m_current_lba - SECTORS_TO_JUMP_BACK) : m_current_lba;
(m_current_lba >= BASE_SECTORS_PER_TRACK) ? (m_current_lba - BASE_SECTORS_PER_TRACK) : m_current_lba;
if (m_physical_lba < base)
m_physical_lba = base;
const CDImage::LBA old_offset = m_physical_lba - base;
const CDImage::LBA new_offset = (old_offset + sector_diff) % SECTORS_TO_JUMP_BACK;
const CDImage::LBA new_offset = (old_offset + sector_diff) % BASE_SECTORS_PER_TRACK;
const CDImage::LBA new_physical_lba = base + new_offset;
#ifdef _DEBUG
const CDImage::Position old_pos(CDImage::Position::FromLBA(m_physical_lba));

5
src/core/cdrom.h
View file

@ -83,7 +83,10 @@ private:
MOTOR_ON_RESPONSE_TICKS = 400000,
MAX_FAST_FORWARD_RATE = 12,
FAST_FORWARD_RATE_STEP = 4
FAST_FORWARD_RATE_STEP = 4,
// Actually varies depending the distance into the disc.
BASE_SECTORS_PER_TRACK = 9,
};
static constexpr u8 INTERRUPT_REGISTER_MASK = 0x1F;