4. Programming notes

The following are notes on playing using this library.

(1) Precautions for creating an application

• This library uses CPU DMA and timer. When operating this library, do not use the DMA and timer of the CPU.

• The frequency of calling PCM_Task should be at least the frequency of V blank interrupts (1 time / 16ms) or more.
  If the same sound is heard twice, it is possible that you call PCM_Task infrequently.

• PCM_Task You can set the upper limit of the amount to be processed by one call with the function PCM_Set1TaskSample. This will stabilize the load on the PCM_Task function.

(2) Relationship with other libraries

• This library uses the file system, stream system, DMA library, and ADPCM decompression library. Link these libraries.

(3) How to take a buffer

• Please secure the following sizes.

  Work buffer	: The size of the work structure.
  Ring buffer	: Minimum (sector size) * 10 [byte]. An integer multiple of the sector size. 1 sector = 2324 bytes for CD-ROM XA Audio playback. Otherwise, 1 sector = 2048 bytes.
  PCM buffer	: 4096 * 2 to 4096 * 4 [sample / 1ch].
  Work for pose processing	: At least 4096 [sample]. Optimal for the same size as the PCM buffer.

(4) Seamless branch

• When seamlessly branched with PCM_EntryNext, the PCM volume and PAN will be the same as the previous handle.

• When seamlessly branching with PCM_EntryNext , you can play continuously for up to 60 minutes. No further continuous playback is possible.

• For seamless branching, use the application program to pre-read the file.

• If you use a file system, you cannot use the seamless branch function.

• Seamless branching can only be done during single playback. It cannot be executed during multi-playback.

(5) Multi playback

• For multi-playback, set the PCM stream playback number to a different number.

• When playing multiple files on a CD at the same time, use file interleaving or channel interleaving. In that case, use the stream system.

• The same file cannot be played multiple times. Please specify a different file.

• You can play up to 4 multiplayers at the same time.

• Only one ADPCM compressed data can be played.

(6) ADPCM compatible

• Link the ADPCM decompression library SEGA_ADP.LIB.

• Call the ADPCM usage declaration PCM_DeclareUseAdpcm next to the initialization function.

◆ Playback of specified ADPCM format

• It can be played with exactly the same procedure (same program) as the AIFF format. However, keep in mind that the CPU load will be higher than in the AIFF format.

◆ CD-ROM XA Audio format playback

• The library determines the playback frequency and the number of channels (stereo / monaural) from the coding information in the subheader area. Make sure it is written correctly.

• The stream key is set by the library user.

• The ring buffer should be an integral multiple of the sector size of 2324 bytes.

• Set the playback information with PCM_SetInfo.

• CD_ROM XA Audio playback can only be used in stream playback mode.

• Please refer to the sample program smppcm5.c.

(7) How to use the function

• Be sure to call PCM_Init at the beginning of the program.

• Be sure to call PCM_VblIn in the V blank IN interrupt.

• PCM_Start can only be run once on a handle.
  If you want to play the same file over and over, generate a handle each time.

• Call PCM_SetLoadNum and PCM_SetPcmStreamNo before starting playback.

• Be sure to use PCM_NotifyWriteSize for the handle generated by PCM_CreateMemHandle to notify the amount of data supplied to the ring buffer.

• To use the pause function, it is necessary to specify the work for pause processing by PCM_SetPauseWork in advance. This work does not need to be prepared for each handle.
  Since this work is a work area that is temporarily used during the pause-on process, you may reserve the area immediately before the pause-on process and release the area immediately after that.

• Data transfer method from the CD block to the ring buffer By default, data is transferred by the DMA of the CPU.
  PCM_SetTrModeCd allows you to specify either program transfer, CPU DMA, or SCU DMA.
  Call PCM_SetTrModeCd after creating the handle and before calling the task function for the first time.

• When playing a CD-ROM XA Audio, be sure to set the playback information with PCM_SetInfo.

(8) About Saturn PCM format

(a) Data creation

• Convert and create AIFF files with the conversion tool AIF2SAP.

[Format]

aif2sap aiffile [sapfile]

[input]

aiffile: AIFF file name
sapfile: SaturnPCM file name

[function]

Convert AIFF files to SaturnPCM files (SAP files).
If you do not enter the SaturnPCM file name, a SaturnPCM file is created with the base name of the AIFF file name with the extension " SAP" added.

(b) Data format

• Uncompressed PCM.

• It has a sector boundary structure.

• The first 2048 bytes is the header area. After that, PCM data is arranged in the order of L channel and R channel in units of 4096 samples.

(c) How to use

• The SaturnPCM format has two playback modes: file playback mode (using a file system) and stream playback mode (using a stream system).

• Next to the initialization function, the SaturnPCM format can be used by calling the function PCM_DeclareUseSapGfs that declares the use of SaturnPCM in file playback mode, and the function PCM_DeclareUseSapStm in stream playback mode.

• After declaring the use of SaturnPCM, you can use it in the same procedure as the AIFF format.

• For specific usage, refer to the sample programs smppcm41.c (file playback mode) and smppcm21.c (stream playback mode).

(d) Regarding resources used

• The default setting is to use SCU-DMA (channel 0) to transfer data from the CD buffer to the sound memory. The data transfer method can be specified as program transfer, CPU-DMA, or SCU-DMA by the function PCM_SetTrModeCd.

(e) Work area

• The SaturnPCM format does not require a ring buffer and instead requires an extended work buffer (extended work buffer size is 2048 bytes).

(f) Restrictions

• The SaturnPCM format and the AIFF / ADPCM / CD-ROM XA Audio format cannot be used at the same time. After declaring the use of SaturnPCM, all PCM files to be played will be in SaturnPCM format.