==================================使用说明===============================================
Readme:
There are 2 midi music inside. 
1. You can select one by masking the other( see below) in dobblebuffering.c. Then compile this prj.

//char *midi_file = (char *)(0x2200000 + .....); 
//const U32 midi_file_end = 0x2200000+ .....;
//#define DELAY_TIME 4000

char *midi_file = (char *)(0x2200000 + ......);  
const U32 midi_file_end = 0x2200000+.....;
#define DELAY_TIME 5500
更改MIDI文件的首尾地址和延时
更改m_ch_instr[] 定位乐器表

2. From VIDE->TOOLS->Sdownload, select com1, press connect. Select *.dmp. Key in downlaod address of 0x2200000, then downlaod. After that quit it.

3. In VIDE, press debugger. choose 38400, com1, load. Then run.
You can hear midi music.

Remark: *.dmp includes piano wave table and it has Grand_piano just C3 C4 C5 tone.
Midi file is also included in *.dmp. 
XGAL1.txt and 1897a.txt are midi file.
*.txt includes address of each file in *.dmp.
========================================================================================	



VG2有<4M的波表空间,采样都为一致如S16位44100(大），11025...
copy波表到TMEM的音频空间
=============================================
播放一个音时：填充地址，频率，长度，时间，模式，音量。
typedef struct tagDgSndChannel
{
	// Software Registers
	U8		MidiChannel, Note;
	U32		Velocity;
	// Hardware Channel Register
	S32		CurSAddr;			// 22.10
	S32		dSAddr;				// 6.10
	S32		dLoop, LoopEnd, LoopBegin;	// 22
	U8		LoopDir;			// 1
	S32		EnvVol;				// S.7.16
	U8		EnvStage;			// 4
	S16		LChnVol, RChnVol;		// 7
	U8		Mode;				// 7
	S32		EnvRate[4];			// S.0.16
	U8		EnvTarget[4];			// 7
} _DGSNDCHANNEL;
播放完后有中断，记录CHANNEL和下一个播放的TONE，做一个数组SIZE=32*5=160
（present_note, freg_number,CHANNEL，NEXT_TONE，vol),及时更新。播完清除。
 MIDI3完成
是双音包罗的，再播放包罗的余音，用NOTE ON / OFF来控制时间长短。
==================================
用一定时器产生***MS的中断，设计一个时钟。用TIMER0
节拍到了就播放一个音。或停一个音。
MIDI4完成
==================================
读MIDI  TXT文件分析
做一个结构树组。
typedef struct MIDI_TONE
{
	U16     md_time;        //开始的时间
        U8      onoff;  //开，关
        U8      md_ch;
        U8      md_note_number;
        U8      md_volume;

	U32	midi_add;	// a pointer of sound data that must be in VR0 Memory.
	U32	midi_freq;	// frequency of data
	U32	midi_len;	// data length
	U8	midi_mode;	// play mode
	U8	VG_channel;	// It'll be set by playmidi
} _MIDI_TONE;
构成32个循环队列，有头尾指针。
先读MIDI文件，先添1个。
MIDI5  finished
播放一个，补上一个。移动指针。
==================================
播放：
时间 == md_time，如为ON 开始播放。
时间 == md_time，如为Off 停止播放，要向回找CH和NOTE相等的，把CH NOTEOFF。
==================================
MIDI17改用WIN的GM.DLS波表实验
首先是吉他OK
将波表用Miles Sound Tools抽取出WAV和RAW
用Audio Compositor分析SAMPLE RATE=22050，LOOP S 和LOOP E
波表为10.DMP，10_a.dmp 10_b.dmp
-----------------------
调试方法：在MAIN（）
if(PlayMidi(midiaddress, midiloopbegin, midi_note[md_temp_1][frequency_number], midilength, midivol, mode)==vgFALSE)
	break;// erro设置BP
在MIDI_1.c中的函数midi_read（）
  vgSndStopChannel(midi_tone[md_f_p].VG_channel); //CLOSE CH
设置BP
程序停下后检查：md_r_p, md_f_p , midi_tone[md_r_p]的值
RELEASE
=========================
MIDI18测试弦乐,大小提琴，用11.DMP波表,11_a.dmp,11_b.dmp
Release
=========================
=========================