world of sound Spectrum - Chapter 6.2: Programming effects and music under the musical coprocessor AY- 3-8910 (AY-3-8912).

<b>world of sound Spectrum</b> - Chapter 6.2: Programming effects and music under the musical coprocessor AY-
3-8910 (AY-3-8912).

          6.2. Programming


   All sound effects and music programmed by the constant 
change of values registers with appropriate delays. Realize 
this may, for example, such a subroutine: 1415.

 10 LD HL, 60000; HL = address of data
 20 LOOP LD A, (HL); A = data bytes
 30 INC HL; HL = HL +1
 40 CP 255; A = 255?
 50 RET Z; if so, return
 60 CP 16; A = 16?
 70 JR NZ, REG; if not, go to the REG
 80 LD B, (HL); B = pause duration
 90 PAUSE HALT; interrupt latency
100 DJNZ PAUSE; cycle
110 JR CONT; go to the CONT
120 REG LD BC, 65533; BC = port address register
130 OUT (C), A; write register number
140 LD B, 191; BC = address data port
150 LD A, (HL); A = register value
160 OUT (C), A; write data to register
170 CONT INC HL; HL = HL +1
180 JR LOOP; go to top
2

   This software is quite primitive, and
to play the music does not really fit, but to create simple 
effects - in most times. Before its launch do not forget

prepare a data block at 60000,
consisting of pairs of data and ending
number 255. The first value in each pair must be a register 
number and the second - number to be written in the register. 
In addition, if the first value equals 16, the second is 
interpreted as delay (in the fifties of a second).


   For music, use much more complex routines like
usually employed in the second interrupt mode. Data for these 
routines are usually stored in a much more comfortable form 
separately for each of the three channels. Result in completely 
even the simplest example of such routines in this book is not 
possible because of its complexity, but if you are familiar with

assembler, you should not write anything
a routine, and I can tell,
how to do it.

   First, consider the format of the data. I
propose the following system: a melody will be given three (the 
number of votes) the basic building blocks of data. Since 
practically any melody consists of identical fragments repeated 
in different orders, it would be logical in the main unit 
itself does not define a melody, and the addresses of such 
fragments. These fragments are usually called patterns (pattern 
- a stencil, template). 

   So, in the main unit may contain the following byte values:

 65,535 (# FFFF) - end of melodies
 0 (# 0000) - the beginning of the cycle
 addr (# XXXX) - address of the next pattern


   Code "start cycle" (0) marks the spot
from which begins playing the melody with repetition.

   Now for patterns. Without going into the theory, give me 
developed Format:


 128 (# 80) - end of pattern
 129, n (# 81, # XX) - set the duration of n
 130, n (# 82, # XX) - noise with a frequency of n (0 ... 31)
 131, n1, n2 (# 83, # XX, # XX) - noise with a frequency of n 
(0 ... 31) + 

                                 note (0 ... 100)
 132, n1, n2 (# 84, # XX, # XX) - a direct frequency reference 
tone 

                                 (0 ... 4095)
 133, addr (# 85, # XXXX) - a task unit frequency change

                                 tone
 134, addr (# 86, # XXXX) - a task unit frequency change

                                 noise
 135, addr (# 87, # XXXX) - a task block changes

                                 Volume
 136, n1, n2, n3 (# 88, # XX, # XXXX) - generator control

                                 envelope
 0 ... 100 (# 00 ... # 64) - Notes from the LA subkontroktavy


   Let me explain some of the codes:

129 - As you probably noticed, when a
      Denmark notes its duration does not indicate
      is called. The fact that it uses
      Xia duration, set wages
      it with this command. Length
      sensitivity is measured in the Fifties

      fractions of seconds.
131 - With this code, you may one
      simultaneously reproduce the tone and noise.
133,134,135 - These codes specify additional
      blocks of data are positive, indicating

      how to change the tone frequency, time
      quency noise and the volume for

      Playing music. If, after the code 133

      or 134 instead of the address block is
      Xia 0, then change the frequency off
      Xia. A number from 0 to 15 after the code 135

      indicates the need for maintaining
      of constant volume,

      corresponding to this number.
136 - This code controls the generator envelope
      envelope. After him, should we find
      ditsya-byte integer from 0 to 7,

      indicating the shape of the envelope in

      According to Table 5 and dvuhbay
      tovoe number specifying the period of change
      of the envelope.
0 ... 100 - These codes define notes. Code 0

      corresponds to the note LA subkontrokta
      you, 1 - LA # 2 - SR, etc.


   The unit, which describes the change in frequency
tone, use the following values:

 128 (# 80) - end of block
-127 ... 127 (# 81 ... # 79) - the frequency shift


   Block frequency noise will be given in the following format:

 128 (# 80) - end of block
-31 ... 31 (# E1 ... # 1F) - the frequency shift


   A unit volume changes let defined as follows:

 128 (# 80) - end of block
 0 ... 15 (# 00 ... # 0F) - meaning the volume


   It is quite logical to make this procedure works in the 
second interrupt mode. Based on this, as well as from the 
proposed format of the data, we can see that for each channel 
will need an array of variables. I suggest the following format:



  offset size value


      0 2 start address of the main block of data

      February 2 current address in the main block of data

      February 4 starting block address changes tone frequency

      June 2 current address in the block frequency tone

      Aug. 2 starting address block frequency noise

     February 10 current address in the block frequency noise

     Feb. 12 start address unit volume changes

     February 14 current address in the block volume changes

     February 16 current address in the current pattern

     18 January value of the current duration

     January 19 meter length

     January 20 the number of remaining repetitions


   In addition, it will take another three bytes for each 
channel for storing tempo count rate and the flag resolution 
sound. 

   The package will include the following
Procedure:

SINIT - Initializing tables, connection

        second mode interrupts.
SSTOP - Off coprocessor, restore
        resistivity standard mode interrupt
        vany.
SNEW - Run all three channels. If you
        call of this subroutine in Regis
        fuck HL, DE and BC should be Adre
        sa major blocks of data for the channel
        crystals A, B and C, respectively. As a result
        Giustra A should be the number of

        repetitions tunes from 1 to 254 or

        255 if you want to chalk
        Diya was repeated endlessly.
SNEWA - Starting channel A. In the register HL

        should be addressed to the data block and

        in case A - the number of repetitions

        (Similarly SNEW). Working channels

        B and C, this procedure without affecting
        em.
SNEWB - Starting channel B. All the same

        SNEWA.
SNEWC - Starting channel C. All the same

        SNEWA.
MUTE - ban / permit work. In Regis
        A triangle should be the channel number of

        0 to 2 or 3, if you are applying

        to all channels. In case B USD
        wives to be code modes: 0 -

        stop, 1 - noiseless,

        2 - playing.
STATUS - Getting the state of the channel. As a result
        Giustra A should be the channel number

        from 0 to 2. On return from space
        A procedure STATUS register contains

        code mode selected channel
        la (similar to B in MUTE).
TEMPO - Setting the pace. In case A USD
        wives to be the channel number from 0 to 2

        or 3, if you are applying to all

        channels. In case B should we find
        ditsya tempo.


  Thus, the beginning of the package might look like:
1415.

  10 ORG 60000

  20 JP SINIT

  30 JP SSTOP

  40 JP SNEW

  50 JP SNEWA

  60 JP SNEWB

  70 JP SNEWC

  80 JP MUTE

  90 JP STATUS
2

   TEMPO procedure might look like:
1415.
 100 TEMPO DI
 110 PUSH HL
 120 PUSH AF
 130 LD HL, TEMPS; HL = pointer to the pace
 140 CP A, 3
 150 JR Z, TEMP3
 160 ADD A, L
 170 LD L, A
 180 JR NC, TEMP1
 190 INC H
 200 TEMP1 LD (HL), B
 210 INC HL
 220 INC HL
 230 INC HL
 240 LD (HL), B
 250 TEMP2 POP AF
 260 POP HL
 270 EI
 280 RET
 290 TEMP3 PUSH DE
 300 LD D, 6
 310 TEMP4 LD (HL), B
 320 INC HL
 330 DEC D
 340 JR NZ, TEMP4
 350 POP DE
 360 JR TEMP2
2

   Since I went to data access, it is necessary
result in line with their description:
1415.
 370 CHAN_A DEFS 21; array of variables for channel A
 380 CHAN_B DEFS 21; array of variables for channel B
 390 CHAN_C DEFS 21; array of variables for the channel C
 400 MUTS DEFS 3; flags permit sound
 410 TEMPS DEFS 3; rate
 420 CURTS DEFS 3; counters rates
 430 AYREGS DEFS 14; copies of registers of a coprocessor
 440 ENVS DEFB 0,4,11,13,8,12,14,10; the envelope
 450 SVOLS DEFW # 8000, # 8001, # 8002; table changes 460 DEFW 
# 8003, # 8004 # 8005; of volume  470 DEFW # 8006, # 8007, # 
8008; standard  480 DEFW # 8009, # 800A, # 800B; values

 490 DEFW # 800C, # 800D, # 800E
 500 DEFW # 800F
 510 NOTES DEFW ... ; Here to write all the values
                           ; Of Table 9 from the upper left

                           ; Angle in order from top - down, 
which is valid                            ; Islands - left

2

   Line 430 contains the domain data that is used for audio 
output. First, it formed the values of all registers of a 
coprocessor with the following subprograms:

1415.
 520 SETAY PUSH HL
 530 PUSH AF
 540 LD AL, AYREGS
 550 ADD A, L
 560 LD L, A
 570 JR NC, SETAY1
 580 INC HL
 590 SETAY1 LD (HL), B
 600 POP AF
 610 POP HL
 620 RET
2

   She needed to pass the register number in A and
its value in B.

   The contents of this field is copied in real coprocessor 
registers another subroutine:

1415.
 630 AYOUT PUSH HL
 640 PUSH DE
 650 PUSH BC
 660 LD HL, AYREGS +13
 670 LD D, 13
 680 AYOUT1 LD BC, 65533
 690 OUT (C), D
 700 LD B, 191
 710 LD E, (HL)
 720 OUT (C), E
 730 DEC HL
 740 DEC D
 750 JP P, AYOUT1; if D> = 0, then go to

                                    AYOUT1
 760 POP BC
 770 POP DE
 780 POP HL
 790 RET
2

   Any of the registers in this area
also read:
1415.
 800 GETAY PUSH HL
 810 PUSH AF
 820 LD HL, AYREGS
 830 ADD A, L
 840 LD L, A
 850 JR NC, GETAY1
 860 INC H
 870 GETAY1 LD B, (HL)
 880 POP AF
 890 POP HL
 900 RET
2

   This routine must pass number
required to register A and she will return it
value B.


   Line 440 needed to decrypt
package envelope. If any number of tables 5 added to the label 
ENVS and upon receipt of the address read one byte, you get a 
value that should be written in R13. 

   Line 450 will need to decrypt
standard volume levels. For this
be a number from 0 to 15 multiplied by 2 (you can use the SLA) 
and add to label SVOLS. The value obtained should be used as 
the address block change the volume. 

   Line 510 will be useful for deciphering the music. If the 
code notes (from 0 to 100) multiplied by 2 (team SLA) and added 
to the label of NOTES, and on the resulting address is 
considered two-byte number, you get the value

junior and senior registers frequency.

   Now for the main procedures:
1415.
 910 STATUS PUSH HL
 920 LD HL, MUTS
 930 ADD A, L
 940 LD L, A
 950 JR NC, STAT1
 960 INC H
 970 STAT1 LD A, (HL)
 980 POP HL
 990 RET
2

   This small but useful procedure
help the programmer to know in what state is this or that 
channel. For example, to find which of them is free. 

   The following procedure - MUTE:
1415.
1000 MUTE DI
1010 PUSH HL
1020 PUSH AF
1030 LD HL, MUTS
1040 CP A, 3
1050 JR Z, MUT2
1060 ADD A, L
1070 LD L, A
1080 JR NC, MUT1
1090 INC H
1100 MUT1 LD (HL), B
1110 POP AF
1120 POP HL
1130 EI
1140 RET
1150 MUT2 LD (HL), B
1160 INC HL
1170 LD (HL), B
1180 INC HL
1190 JR MUT1
2

   This procedure is necessary, for example,
to temporarily stop the work of one of
channels.

   Now - the initialization of channels:
1415.
1200 SNEWC PUSH IX
1210 LD IX, CHAN_C
1220 PUSH BC
1230 LD B, 2
1240 JR SNEW1

1250 SNEWB PUSH IX
1260 LD IX, CHAN_B
1270 PUSH BC
1280 LD B, 1
1290 JR SNEW1

1300 SNEWA PUSH IX
1310 LD IX, CHAN_A
1320 PUSH BC
1330 LD B, 0
1340 SNEW1 DI
1350 PUSH BC
1360 PUSH DE
1370 PUSH HL
1380 PUSH IX
1390 POP HL
1400 PUSH HL
1410 POP DE
1420 INC DE
1430 LD BC, 20
1440 LD (HL), B
1450 LDIR
1460 POP HL
1470 PUSH HL
1480 LD (IX +20), A
1490 LD (IX +0), L
1500 LD (IX +1), H
1510 LD (IX +19), 0
1520 LD E, (HL)
1530 INC HL
1540 LD D, (HL)
1550 INC HL
1560 LD (IX +2), L
1570 LD (IX +3), H
1580 LD (IX +16), E
1590 LD (IX +17), D
1600 LD HL, SVOLS +30
1610 LD (IX +12), L
1620 LD (IX +13), H
1630 LD (IX +14), L
1640 LD (IX +15), H
1650 LD (IX +18), 13; the duration of the default

                                      = 1 / 4
1660 POP HL
1670 POP DE
1680 POP BC
1690 LD A, B
1700 LD B, 2
1710 CALL MUTE
1720 LD B, 1
1730 CALL TEMPO
1740 POP BC
1750 POP IX
1760 EI
1770 RET
2

   And finally, initialize all three channels:
1415.
1780 SNEW PUSH HL
1790 CALL SNEWA
1800 PUSH DE
1810 POP HL
1820 CALL SNEWB
1830 PUSH BC
1840 POP HL
1850 CALL SNEWC
1860 POP HL
1870 RET
2

   Initialization routines to prepare the arrays of variables 
necessary for the data. They set block addresses frequency 
tones and noise in the "not used" (will wear they 0). Choose a 
constant level volume (15). And also set the duration of notes 
by default equal to 1 / 4 seconds. 

   That routine connect a second
Interrupt mode:
1415.
1880 SINIT LD A, 24
1890 LD (65535), A
1900 LD A, 195
1910 LD (65524), A
1920 LD HL, INTR; HL = address of handler
1930 LD (65525), HL
1940 LD HL, 65024
1950 LD DE, 65025
1960 LD BC, 256
1970 LD (HL), 255
1980 LD A, H
1990 LDIR
2000 DI
2010 LD I, A
2020 IM 2
2030 LD HL, MUTS; ban
2040 XOR A
2050 LD (HL), A; work
2060 INC HL
2070 LD (HL), A; all
2080 INC HL
2090 LD (HL), A; channels
2100 EI
2110 RET
2

   This subroutine returns the standard mode interrupts on and 
off coprocessor:

1415.
2120 SSTOP DI
2130 LD A, 63
2140 LD I, A
2150 IM 1
2160 EI
2170 LD HL, AYREGS
2180 LD DE, AYREGS +1
2190 LD BC, 13
2200 LD (HL), B; B = 0
2210 LDIR; cleaning of registers
2220 LD A, 7
2230 DEC B; B = 255
2240 CALL SETAY; R7 = 255 (off mixer)
2250 JP AYOUT; output registers in the coprocessor
2

   Now let us interrupt handler. Since he must serve three 
channels, and arrays of variables is most easily addressed 
registers IX, we can propose this routine:

1415.
2260 INTR PUSH AF; preservation registers
2270 PUSH HL
2280 PUSH DE
2290 PUSH BC
2300 PUSH IX
2310 LD IX, CHAN_A; training registers
2320 XOR A
2330 CALL DISPAT; coprocessor
2340 LD IX, CHAN_B
2350 LD A, 1 for all channels
2360 CALL DISPAT
2370 LD IX, CHAN_C
2380 LD A, 2
2390 CALL DISPAT
2400 CALL AYOUT; output registers in the coprocessor
2410 POP IX; restore registers
2420 POP BC
2430 POP DE
2440 POP HL
2450 POP AF
2460 RST 56; standard call handler
2470 RET
2

   This handler for each channel
calls the dispatcher (DISPAT), holding up to register A channel 
number, and register IX - the array address of its variables.


   Role DISPAT procedure is to process variables TEMPS, CURTS 
and MUTS for specified channel, as well as to call the main 
subroutine creation of sound - GETSND. 

   Here is the text of procedure DISPAT:
1415.
2480 DISPAT PUSH AF
2490 LD E, A
2500 LD D, 0
2510 CALL STATUS
2520 OR A; channel stopped?
2530 JR NZ, DISP1
2540 POP AF
2550 LD B, A
2560 JR DISP3
2570 DISP1 LD HL, CURTS
2580 ADD HL, DE
2590 LD A, (HL)
2600 OR A
2610 JR Z, DISP2
2620 DEC (HL); reduction in the rate meter
2630 POP AF
2640 RET
2650 DISP2 DEC HL; update
2660 DEC HL
2670 DEC HL; counter
2680 LD A, (HL)
2690 INC HL; rate
2700 INC HL
2710 INC HL
2720 LD (HL), A
2730 POP AF
2740 CALL GETSND; challenge the basic procedure
2750 LD B, A
2760 CALL STATUS
2770 CP 1; should "drown out"?
2780 RET NZ
2790 DISP3 LD C, B; "mute"
2800 LD HL, AYREGS +6
2810 LD A, 9; channel
2820 DISP4 SLA A
2830 DJNZ DISP4
2840 OR (HL)
2850 LD (HL), A
2860 INC HL
2870 ADD HL, BC
2880 LD (HL), 0
2890 RET
2

   So, all service procedures are given. Only one left - GETSND:
1415.
2900 GETSND ...
2

   That is what I propose to write to you.
But do not worry - I'll explain everything in detail.

   Most likely, the procedure will GETSND
is sufficiently large. Perhaps even more
of all these procedures together.
But there is nothing difficult in it does not, and its volume
due to the rather complex format
data.

   The task procedure GETSND reduces the formation of certain 
cells of AYREGS data of one channel for subsequent copying into 
registers coprocessor. 

   The details of this procedure
transferred to the channel number in register A (that she knew 
of any place cells data for the frequency, volume, etc.) and

address of an array of variables in the register IX.
Note that it is obliged to preserve the value of the register 
A! You may even have to make an additional variable to store it.


   Thus, the procedure in the procedure
GETSND the following:

 1. Check if there is zero counter

    duration (IX +19).
 2. If not, then continue playback
    of the current note.
 3. If equal, then select a new note and

    start its playback.


   The term "resume playback
current notes "includes the following:

 1. Reduce the length of the counter.
 2. If the address of one of the additional

    blocks is 0, items 3 ... 5 for

    this unit perform is not necessary.
 3. Choose the next value of the blocks

    Frequency and volume, using
    Using variables IX +6 / IX +7, IX +10 / IX +11

    and IX +14 / IX +15.
 4. In accordance with the selected values
    mi and the channel number with the update on the
    aid procedures and GETAY SETAY Region

    AYREGS (note that the bias
    the frequencies may be negative
    mi).
 5. Update variables to addresses IX +6 /

    IX +7, IX +10 / IX +11 and IX +14 / IX +15 in with
    correspondence with paragraph 3.


   Start playback of music "includes
in itself is only one item:

 1. Rewrite the variables to addresses IX +4 /

    IX +5, IX +8 / IX +9, IX +12 / IX +13 and IX +18 in

    their counters - doubles (IX +6 / IX +7, IX +10 /

    IX +11, IX +14 / IX +15 and IX +19).


   But the point to choose a new note - a little more 
complicated: 

 1. Choose the next byte from the current

    pattern (e - IX +16 / IX +17).
 2. If it is not equal to 0 ... 100, 130, 131 and

    132 - treat as appropriate

    control code and go to Step 1.
 3. Accordingly, a byte or a couple
    meters and the channel number of the update
    AYREGS region and a variable IX +16 / IX +17.


   Now, the processing control codes:


   Code 128:

 1. Choose the address of the next pattern of

    the main unit (addressed mostly to block
    Ke contained in IX +2 / IX +3).
 2. Update variable IX +2 / IX +3.
 3. If the address pattern is zero, Skopje
    rovat variable IX +2 / IX +3 in IX +0 / IX +

    1 and go to Step 1.
 4. If the address is 65535, copy

    variable IX +0 / IX +1 in IX +2 / IX +3 and

    reduce the repeat count (IX +20).

    If the repeat count is zero,

    set the channel state to stop
    Flax "by the procedure of MUTE. Continue

    to step 1.
 5. Record the selected address in IX +16 / IX +17

    and select a new note. "


   Code 129:

 1. Get byte, followed by this code, and

    recorded in the IX +18. Select a new note. "


   Code 133 (134):

 1. Get address, followed by this code,

    and put it in the IX +4 / IX +5 (IX +8 / IX +

    9). Select a new note. "


   Code 135:

 1. Get address, followed by this code.
 2. If it is less than 16, calculate the corresponding
    corresponding address in the table SVOLS.
 3. Put the probe in IX +12 / IX +

    13.
 4. Select a new note. "


   Code 136:

 1. Set in the register of the volume set
    of the channel to 16.

 2. Write to IX +14 / IX +15 zero.
 3. Get byte, followed by this code.
 4. Calculate the table ENVS value R13

    and renew the domain AYREGS.
 5. Take the two bytes following the code

    forms and bring them into the cells 11 and 12

    area AYREGS.
 6. Select a new note. "


   Now how can calculate the number of registers for a given 
channel. To calculate the number of the register of frequency, 
rather channel number multiplied by 2 (ADD A, A). Resulting 
number is the number register Low Byte frequency. To get the 
register number of the byte in the frequency, the value should 
be increased by 1 (INC A).


   To calculate the volume number of the register, it is 
necessary to add the channel number 8 (ADD A, 8).


   If you write a procedure GETSND, in
Your hands will be quite a powerful program, suitable for 
writing both music and effects.


   And at the end of the description of this program - tips on 
compiling the data blocks for her. 

   To raise or lower the note one octave, its value must be 
correspondingly increased or decreased by 12. Note BEFORE the 
first octave corresponds to the number 39. 

   The values of the durations you can take
Table 11.

   Now, some tips on programming a coprocessor. For the 
formation of new sounds you can use the generator envelope that 
is configured to periodically change the volume and greater 
frequency. Particularly good results can be achieved by 
configuring it at multiples frequency of the main signal.


   To mute the music co-processor is often used prohibition
all functions of the mixer (output byte 255
R7), but this method is not very reliable.
If the envelope generator is configured to periodically change 
the volume, then this the trick will not work: will be audible 
click. For a complete silencing of a coprocessor can recommend 
a routine: 1415.

 10 LD HL, DATA; HL = address of data
 20 LD E, 10; E = number of first register
 30 LOOP LD BC, 65533; BC = port address register
 40 OUT (C), E; output port E in BC
 50 LD A, (HL); A = value of the next

                                    Register
 60 LD B, 191; BC = address data port
 70 OUT (C), A; output to port A BC
 80 INC HL; HL = HL +1
 90 DEC E; E = E-1
100 LD A, E; E =
110 CP; 6 6?
120 JR NZ, LOOP; if not, then the cycle
130 RET; Returns
140 DATA DEFB 0,0,0,255; data registers AY
2

   In many cases, required to determine
whether there is a coprocessor to the computer. Some do it by 
checking the type of computer (48K/128K), but this method does 
not quite fair, since AY can stand and

the good old Spectrum. Here is a subroutine, which determines 
the presence of a coprocessor more reliably: 1415.

 10 LD BC, 65533; BC = port address register
 20 XOR A; A = 0
 30 OUT (C), A; selection register 0
 40 LD B, 191; BC = address data port
 50 OUT (C), A; output 0 in the selected case
 60 LD B, 255; BC = port address register
 70 IN A, (C); input values from the selected

                                    Register
 80 OR A; A = 0?
 90 RET; Returns
2

   If after calling this subroutine
Z flag is cleared, then the coprocessor is present. Otherwise - 
no. 

   And finally I want to tell you about one
very interesting technique. It is often used in many programs. 
Reading data from the registers are up and converting them 
appropriately in graphical information along with music 
playback, you can make soundlights or peak signal level.