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=============================================================================
*** How to use ***
You need to take "src-68k/echo.68k" and include it in your program. Then you
need to take "built/prog-z80.bin" (or if you built Echo from source, the
generated binary). Finally, go to the echo.68k file, look for @Z80Program
(should be near the end of the file) and change the filename to point where
the prog-z80.bin file is.
Echo should now be inside your program. Now call Echo_Init (see below) to
initialize Echo and load the instrument list, and then you can proceed to use
Echo as needed (e.g. call Echo_PlayBGM to start playing music).
Unless stated otherwise, calling the API subroutines will *not* modify the
68000 registers.
=============================================================================
*** Initialization ***
Echo_Init
Initializes Echo. Loads the instrument list, loads the Z80 engine and gets
it running. You need to call this before you can use Echo (usually when
the program is just starting).
The address of the instrument list is given in register a0. The instrument
list can be built using the Echo_List* macros. An example of a short
instrument list is as follows:
Echo_ListEntry instrument1
Echo_ListEntry instrument2
Echo_ListEntry instrument3
Echo_ListEnd
Where the parameter for Echo_ListEntry is the address (e.g. a label) to
the EIF/EEF/EWF data of the instrument.
=============================================================================
*** Background music ***
Echo_PlayBGM
Starts playback of the specified background music. The register a0 points
to the ESF data for the background music.
Echo_StopBGM
Stops playback of background music. Used both to stop and to pause music
(the latter can be undone with Echo_ResumeBGM, see below).
Echo_ResumeBGM
Resumes playback of whatever background music was playing last time before
Echo_StopBGM was called. Used when you want to unpause music.
=============================================================================
*** Sound effects ***
Echo_PlaySFX
Starts playback of the specified sound effect. The register a0 points to
the ESF data for the sound effect.
Echo_StopSFX
Stops playback of sound effects.
=============================================================================
*** Control ***
Echo_GetStatus
Gets the current status of Echo. The status is returned as a word in d0,
with the following bits set as relevant:
Bit 0 .... Sound effect is playing
Bit 1 .... Background music is playing
Bit 15 ... Echo is busy (can't take commands)
The API will automatically wait if you try to send a command while Echo is
busy, so the only reason to check for that is if you don't want to halt
the 68000 until Echo is ready to take more commands.
=============================================================================
*** Settings ***
Echo_SetPCMRate
Changes the sample rate of PCM. Note this is a global parameter as it
affects both BGM and SFX. The value is what one would write in timer A of
the YM2612 register. Here are the approximate frequencies for some values
(default is $05):
NTSC PAL | NTSC PAL
----------------------------|--------------------------
$02 ... 26632Hz ... 26389Hz | $08 ... 6658Hz ... 6597Hz
$03 ... 17755Hz ... 17593Hz | $09 ... 5918Hz ... 5864Hz
$04 ... 13316Hz ... 13194Hz | $0A ... 5326Hz ... 5278Hz
$05 ... 10653Hz ... 10556Hz | $0B ... 4842Hz ... 4798Hz
$06 .... 8877Hz .... 8796Hz | $0C ... 4439Hz ... 4398Hz
$07 .... 7609Hz .... 7539Hz | $0D ... 4097Hz ... 4060Hz
The higher the sample rate, the better quality, but also takes up more
space and, more importantly, reduces CPU time available for other things
(which can hamper Echo's ability to process complex streams). Be careful
if you increase the sample rate.
=============================================================================
*** Raw access ***
Echo_SendCommand
Sends an argument-less command to Echo. The command ID is given as a byte
in register d0.
Echo_SendCommandAddr
Sends a command to Echo that takes an address as its argument. The command
ID is given as a byte in register d0, while the address argument is given
in register a0.
Echo_SendCommandByte
Sends a command to Echo that takes a byte as its argument. The command ID
is given as a byte in register d0, while the byte argument is given in
register d1.
=============================================================================
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