Refactor the ReelMagic audio FIFO class #2090
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Context: the Sound Blaster's internal frequency can be derived from the Transfer Time constant passed into the 40h call: Time Constant = 65536 - (256 000 000/(channels * sampling rate) - The channels parameter is 1 for mono, 2 for stereo. - Only the high byte of the result is sent to the DSP. Ref: Sound Blaster Series Hardware Programming Guide Set digitized sound transfer time constant, 6-14 DSP Commands https://pdos.csail.mit.edu/6.828/2018/readings/hardware/SoundBlaster.pdf --- If we solve for the sampling rate: 256 000 000 sampling rate = ---------------------------------------- <channels> * (65536 - (<high-byte> << 8)) Where <channels> can be 1 or 2 and <high-byte> 0 to 255. Here's are some sample rates: mono (1 channel) with high-byte 0 => 3 906 Hz mono (1 channel) with high-byte 127 => 7 751 Hz mono (1 channel) with high-byte 166 => 11 111 Hz mono (1 channel) with high-byte 234 => 45 454 Hz mono (1 channel) with high-byte 255 => 1 000 000 Hz stereo (2 channels) with high-byte 0 => 1 953 Hz stereo (2 channels) with high-byte 127 => 3 875 Hz stereo (2 channels) with high-byte 211 => 11 111 Hz stereo (2 channels) with high-byte 245 => 45 454 Hz stereo (2 channels) with high-byte 255 => 500 000 Hz The high-byte passed into 40h is valid for setting DMA rates however the above shows we can't trust it to give us a valid playback rate within the documented 5-45 Khz range. So this commit simply keeps the the sound blaster's requested channel rate between the 5 to 45 KHz range. This can be seen in The Horde ReelMagic edition, which, on initialization, feeds the Sound Blaster a 255-value via 40h, which in turn (previously) asked the mixer channel to run at 1 million Hz :)
The prior code could overflow into a large negative number if the elapsed PIT ticks exceeded the read latch. This would result in the uint32_t wrapping to a value of 4+ billion, exceeding `iround`'s signed integer limit. This occurs in The Horde, ReelMagic edition.
A double free was encountered when shutting down The Horde (ReelMagic edition) using Opus CD-DA tracks.
DOSBox's mixer has (for a very long time) allowed adjustment of a channel's volume through a user control (via MIXER) and by the application (via the SB Mixer), however the names of these member variables and their functions to manage them were often not obvious. This commit renames names these variables and functions to match their purpose. It also adds a third fixed volume scalar to let a channel scale up or down it's samples to get to 0 dB on the signed 16-bit scale, which is used by the ReelMagic and GUS chanels.
This uses current decoded MP2 frame as the FIFO itself without any copying or re-buffering.
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Completed testing on the Pi 4. See recommended settings in the PR comment above (applicable to all systems). Even during playback, the Pi only runs its CPU between ~1.1 - 1.4 GHz to keep up. Here's a 3-second running log of the core's frequency (Hz): |
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The refactored ReelMagic AudioFifo class now loads audio directly into DOSBox Staging's mixer (via pointer from the MPEG stream's decoded interleaved audio buffer) without queuing or math operations performed on the samples.
It now also skips initial gaps in decoded audio.
The ReelMagic's mixer channel is now activated on an as-needed basis.
Playback is working smooth with fewer initial audio hiccups, even at 800 Mhz:
Tips for optimal performance
Use your lowest latency
[sdl]conf settings. If you're using a Raspberry Pi, be sure to use the recommended baseline configs.In addition to the baseline settings, further apply these ReelMagic specific settings, which are suitable for all the ReelMagic games:
Notes: