In the previous section , we understood the usage of tags, aliases, header files/libraries, and macro definitions. Next we will look at two other useful functions: character maps and
.datasegments.
This section refers to Character maps , Local variables and memory segments
Character mapping
C64 uses PETSCII(CBM ASCII) encoding. Different from the ASCIIcode, the most significant difference is that the upper and lower case letters ASCIIare completely reversed compared to the code.
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| PETSCII - Wikipedia |
Therefore, Ophin provides a character mapping function to solve this problem. We can use to .charmapdefine a new character mapping. It has two parameters, which are ASCIIthe character value at the beginning of the mapping + a mapping string in the sequence. For example, the following two lines of code will reverse the case, so you can get the normal output result.
.charmap 'A, "abcdefghijklmnopqrstuvwxyz"
.charmap 'a, "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
Or you can .charmapbindirectly replace the entire character table (256 characters). It accepts a parameter that points to a 256-byte file to illustrate the character mapping relationship.
The following is the 256Byte -> mapping using base16384 encoding .ASCIIPETSCII
一帠娐匆係亐瘬娍冃缁剈愔卅潱湤栛唇忡誀漢囉偒暜瘩墊胂芸細婌焳廔萷導憣竰謾巐吖垍牥枙蒆玩祬楛瓷俅聳欝敧毡蝺擗叕蝽湁庐艄挙啈恒犴缵屏戔挥孑捖揖厕短詽涟蘈吊冄潡癸瀦墋焣曨豂徒狥坙桞暙璦蟉葺涠癨砺悖璧砪梪粲箮秬夛壎芵箭見瓪覼絯秼儇僃缱橬洣埊胳嫜褿廑芴譍敛旘葶箽腷泟蘸氮嶓珦蟺岞禯竭覻贏嗋致譽絿燧裻贿淯言㸾㴽㴽㴽
The binary and hexadecimal codes of printing files in C language are as follows
00000000 00000001 00000010 00000011 00000100 00000101 00000110 00000111 00 01 02 03 04 05 06 07
00001000 00001001 00001010 00001011 00001100 00001101 00001110 00001111 08 09 0a 0b 0c 0d 0e 0f
00010000 00010001 00010010 00010011 00010100 00010101 00010110 00010111 10 11 12 13 14 15 16 17
00011000 00011001 00011010 00011011 00011100 00011101 00011110 00011111 18 19 1a 1b 1c 1d 1e 1f
00100000 00100001 00100010 00100011 00100100 00100101 00100110 00100111 20 21 22 23 24 25 26 27
00101000 00101001 00101010 00101011 00101100 00101101 00101110 00101111 28 29 2a 2b 2c 2d 2e 2f
00110000 00110001 00110010 00110011 00110100 00110101 00110110 00110111 30 31 32 33 34 35 36 37
00111000 00111001 00111010 00111011 00111100 00111101 00111110 00111111 38 39 3a 3b 3c 3d 3e 3f
01000000 01100001 01100010 01100011 01100100 01100101 01100110 01100111 40 61 62 63 64 65 66 67
01101000 01101001 01101010 01101011 01101100 01101101 01101110 01101111 68 69 6a 6b 6c 6d 6e 6f
01110000 01110001 01110010 01110011 01110100 01110101 01110110 01110111 70 71 72 73 74 75 76 77
01111000 01111001 01111010 01011011 01011100 01011101 01011110 01011111 78 79 7a 5b 5c 5d 5e 5f
01100000 01000001 01000010 01000011 01000100 01000101 01000110 01000111 60 41 42 43 44 45 46 47
01001000 01001001 01001010 01001011 01001100 01001101 01001110 01001111 48 49 4a 4b 4c 4d 4e 4f
01010000 01010001 01010010 01010011 01010100 01010101 01010110 01010111 50 51 52 53 54 55 56 57
01011000 01011001 01011010 01111011 01111100 01111101 01111110 01111111 58 59 5a 7b 7c 7d 7e 7f
10000000 10000001 10000010 10000011 10000100 10000101 10000110 10000111 80 81 82 83 84 85 86 87
10001000 10001001 10001010 10001011 10001100 10001101 10001110 10001111 88 89 8a 8b 8c 8d 8e 8f
10010000 10010001 10010010 10010011 10010100 10010101 10010110 10010111 90 91 92 93 94 95 96 97
10011000 10011001 10011010 10011011 10011100 10011101 10011110 10011111 98 99 9a 9b 9c 9d 9e 9f
10100000 10100001 10100010 10100011 10100100 10100101 10100110 10100111 a0 a1 a2 a3 a4 a5 a6 a7
10101000 10101001 10101010 10101011 10101100 10101101 10101110 10101111 a8 a9 aa ab ac ad ae af
10110000 10110001 10110010 10110011 10110100 10110101 10110110 10110111 b0 b1 b2 b3 b4 b5 b6 b7
10111000 10111001 10111010 10111011 10111100 10111101 10111110 10111111 b8 b9 ba bb bc bd be bf
11000000 11000001 11000010 11000011 11000100 11000101 11000110 11000111 c0 c1 c2 c3 c4 c5 c6 c7
11001000 11001001 11001010 11001011 11001100 11001101 11001110 11001111 c8 c9 ca cb cc cd ce cf
11010000 11010001 11010010 11010011 11010100 11010101 11010110 11010111 d0 d1 d2 d3 d4 d5 d6 d7
11011000 11011001 11011010 11011011 11011100 11011101 11011110 11011111 d8 d9 da db dc dd de df
11100000 11100001 11100010 11100011 11100100 11100101 11100110 11100111 e0 e1 e2 e3 e4 e5 e6 e7
11101000 11101001 11101010 11101011 11101100 11101101 11101110 11101111 e8 e9 ea eb ec ed ee ef
11110000 11110001 11110010 11110011 11110100 11110101 11110110 11110111 f0 f1 f2 f3 f4 f5 f6 f7
11111000 11111001 11111010 11111011 11111100 11111101 11111110 11111111 f8 f9 fa fb fc fd fe ff
From this, we can write code that prints lowercase letters
lda #lower'case ; 切换大小写
jsr chrout
The complete code is as follows. It is worth noting that the code uses nopinstructions to define delaymacros to achieve delay.
.include "c64-1.oph"
.outfile "hello.prg"
.macro print
ldx #0
_loop: lda _1, x
beq _done
jsr chrout
inx
bne _loop
_done:
.macend
.macro greet
lda #30
jsr delay
`print hello1
`print _1
`print hello2
.macend
lda #147
jsr chrout
lda #lower'case
jsr chrout
`greet target1
`greet target2
`greet target3
`greet target4
`greet target5
`greet target6
`greet target7
`greet target8
`greet target9
`greet target10
rts
.charmap 'A, "abcdefghijklmnopqrstuvwxyz"
.charmap 'a, "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
hello1: .byte "Hello, ",0
hello2: .byte "!", 13, 0
target1: .byte "programmer", 0
target2: .byte "room", 0
target3: .byte "building", 0
target4: .byte "neighborhood", 0
target5: .byte "city", 0
target6: .byte "nation", 0
target7: .byte "world", 0
target8: .byte "Solar System", 0
target9: .byte "Galaxy", 0
target10: .byte "Universe", 0
; DELAY routine. Executes 2,560*(A) NOP statements.
delay: tax ; x = a
ldy #00 ; y = 0
* nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
iny ; y++
bne -
dex ; x--
bne -
rts
data段
In fact, memory BASIC ROMand I/O ROMbetween there is a free space, located 0xC000- 0xCFFFwe can use this space to store some temporary variables. So Ophis designed .datainstructions to automatically manage this part of the space. However, it does not know where the free space starts, so we need to manually declare
.data
.org $C000
In addition, because it does not know the size of the free space, it will not check the boundary, we need to use the following instructions at the end of the program to notify the compiler to check
.checkpc $A000 ; text段边界
.data
.checkpc $D000 ; data段边界
Then you can use .spacecommands to conveniently manage and use this part of the space
.data ; 切换到data段
.space _a 1 ; 为_a分配1字节空间
.space _b 4 ; 为_b分配4字节空间
.text ; 切换回text段，即机器代码所在段
It is worth noting that although the above comment mentions "allocation", just like the C language, the program or compiler does not check whether the access is out of range. In fact, the compiler just assigns the first address of the existing free space to an "alias" and moves the "free space mark" (PC) backward by the declared length.
Practical application
Next we will introduce a better implementation of nopa delaysubroutine that is different from that defined by instructions . This implementation makes use of KERNALlibrary rdtimsubroutines. This subroutine returns an 24bitinteger, which represents a multiple of the number of seconds that the system is currently powered on 60.
First, let's analyze rdtimthe storage location of the return value. You can execute the following code that will run a print cycle rdtimafter a, x, ythe binary value.
.include "Ophis-2.1/platform/c64header.oph"
.require "Ophis-2.1/platform/c64kernal.oph"
.outfile "clock.prg"
.data
.org $C000
.space _na 1 ; a的临时存放处
.space _nx 1 ; x的临时存放处
.space _ny 1 ; y的临时存放处
.text
* jsr rdtim ; Read Time
stx _nx
sty _ny
jsr printbyte
jsr printspace
lda _nx
jsr printbyte
jsr printspace
lda _ny
jsr printbyte
lda #13 ; 换行
jsr chrout
jmp - ; 死循环
printbyte: ldx #7 ; 打印8bit
sta _na
* lda #$30 ; a = '0'
asl _na ; 左移一位，溢出到c
bcc + ; if(c == 0) goto 下一个星号
adc #0 ; else a = a + c + 0
* jsr chrout ; putchar(a)
dex ; x--
bne -- ; if(x != 0) goto 上两个星号
rts
printspace: lda #$20
jsr chrout
rts
.checkpc $A000
.data
.checkpc $D000
The following results can be observed
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It can be seen that the 24bitinteger will be stored in little-endian order {a, x, y}. Based on this principle, we can amake subroutines 255/60=4.25swhose maximum delay does not exceed through statistical values delay.
; DELAY routine. Takes values from the Accumulator and pauses
; for that many jiffies (1/60th of a second).
.scope
.data
.space _tmp 1
.space _target 1
.text
delay: sta _tmp ; save argument (rdtim destroys it)
jsr rdtim
clc
adc _tmp ; add current time to get target
sta _target
* jsr rdtim
cmp _target
bmi - ; Buzz until target reached
rts
.scend
It is worth noting that the reason why we do not use the following statement to create temporary storage space in the program is to save textthe space of the program segment
.scope
; data used by the delay routine
_tmp: .byte 0
_target: .byte 0
delay: sta _tmp ; save argument (rdtim destroys it)
jsr rdtim
clc
adc _tmp ; add current time to get target
sta _target
* jsr rdtim
cmp _target
bmi - ; Buzz until target reached
rts
.scend
In addition, if there is nothing else in the program, .spacethe two lines of .spacestatements in the above program are equivalent to the following statements
.alias _tmp $C000
.alias _target $C001