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; PRG format
; Contains two bytes of header data, address from which
; the rest of the file will be loaded into memory.
; BASIC memory starts at addr 2048, we effectively place "10 SYS 2064"
; and an end of program after it. Then immedately afterwards
; we place our command on addr 2064.
; When BASIC loads up, it runs "10 SYS 2064" and passes up execution there.
; Then, when we return, we get a zero which indicates termination.
; The starting address is defined by the value (label or alias) "main".
; Since in basic we need to provide a decimal string, but we store a decimal value, we need
; to do this complicated convertion.
.alias main_addr_ch1 '0 + main / 10000 ; 65535 -> 6
.alias main_addr_ch2 '0 + [main - main / 10000 * 10000] / 1000 ; 65535 -> 65535 - 60000 = 5535 / 1000 = 5
.alias main_addr_ch3 '0 + [main - main / 1000 * 1000] / 100 ; 65535 -> 65535 - 65000 = 535 / 100 = 5
.alias main_addr_ch4 '0 + [main - main / 100 * 100] / 10 ; 65535 -> 65535 - 65500 = 35 / 10 = 3
.alias main_addr_ch5 '0 + main - main / 10 * 10 ; 65535 -> 65535 - 65530 = 5
.word $0801 ; Header -- addr 2049
.org $0801 ; Program Counter
.scope
.word _eop ; Next line addr (I guess it is used to tell how long the line is?)
.word 10 ; 10 (line of BASIC program)
.byte $9e," " ; SYS 2064 (opcode for SYS and null terminated string)
.byte main_addr_ch1,main_addr_ch2,main_addr_ch3,main_addr_ch4,main_addr_ch5,0
_eop: .word 0 ; End of program
.scend
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