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When a program starts running, INIT is moved from one place to another place. Then, INIT's code is executed; and, the first place is re-used for variables. After the INIT code has finished, the second place can be re-used by the heap and the C stack. That means that initiation code and data won't waste any RAM space after they stop being needed.
55 lines
1.6 KiB
ArmAsm
55 lines
1.6 KiB
ArmAsm
;
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; 2015-10-04, Greg King
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;
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.export move_init
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.import __INIT_LOAD__, __INIT_RUN__, __INIT_SIZE__ ; Linker-generated
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.importzp init_load_, init_run_
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.macpack cpu
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.macpack generic
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; Move the INIT segment from where it was loaded (over the bss segments)
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; into where it must be run (in the heap). The two areas might overlap; and,
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; the segment is moved upwards. Therefore, this code starts at the highest
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; address, and decrements to the lowest address. The low bytes of the starting
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; pointers are not sums. The high bytes are sums; but, they do not include the
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; carry. Both the low-byte sums and the carries will be done when the pointers
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; are indexed by the .Y register.
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move_init:
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lda #<__INIT_LOAD__
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ldx #>__INIT_LOAD__ + >__INIT_SIZE__
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sta init_load_
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stx init_load_+1
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lda #<__INIT_RUN__
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ldx #>__INIT_RUN__ + >__INIT_SIZE__
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sta init_run_
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stx init_run_+1
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; First, move the last, partial page.
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; Then, move all of the full pages.
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ldx #>__INIT_SIZE__ + 1 ; number of pages, including partial
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ldy #<__INIT_SIZE__ ; size of partial page
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.if .cpu & CPU_ISET_65SC02
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bra L3
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.else
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jmp L3
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.endif
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L1: dec init_load_+1
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dec init_run_+1
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L2: dey
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lda (init_load_),y
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sta (init_run_),y
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tya
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L3: bnz L2 ; page not finished
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dex
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bnz L1 ; move next page
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rts
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