Adapted, to the c64 target, the INIT-segment overlay scheme from the apple2 targets.
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.
This commit is contained in:
Greg King
@@ -3,13 +3,13 @@
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;
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.export _exit
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.exportzp init_load_, init_run_
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.export __STARTUP__ : absolute = 1 ; Mark as startup
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.import initlib, donelib
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.import zerobss
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.import callmain
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.import move_init, zerobss, callmain
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.import RESTOR, BSOUT, CLRCH
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.import __RAM_START__, __RAM_SIZE__ ; Linker generated
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.import __STACKSIZE__ ; Linker generated
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.import __HIMEM__ ; from configure file
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.importzp ST
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.include "zeropage.inc"
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@@ -19,18 +19,17 @@
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; ------------------------------------------------------------------------
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; Startup code
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; Two zero-page pointers are needed before any zero-page stuff is saved.
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; Choose locations that are not used by anything.
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init_load_ := FREKZP
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init_run_ := FREKZP+2
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.segment "STARTUP"
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Start:
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; Save the zero-page locations that we need.
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ldx #zpspace-1
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L1: lda sp,x
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sta zpsave,x
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dex
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bpl L1
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; Switch to the second charset.
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lda #14
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@@ -39,35 +38,30 @@ L1: lda sp,x
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; Switch off the BASIC ROM.
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lda $01
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pha ; Remember the value
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sta mmusave ; Save the memory configuration
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and #$F8
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ora #$06 ; Enable Kernal+I/O, disable BASIC
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sta $01
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; Clear the BSS data.
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jsr zerobss
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; Save some system settings; and, set up the stack.
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pla
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sta mmusave ; Save the memory configuration
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tsx
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stx spsave ; Save the system stack ptr
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lda #<(__RAM_START__ + __RAM_SIZE__ + __STACKSIZE__)
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sta sp
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lda #>(__RAM_START__ + __RAM_SIZE__ + __STACKSIZE__)
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sta sp+1 ; Set argument stack ptr
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; Allow some re-entrancy by skipping the next task if it already was done.
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; This often can let us rerun the program without reloading it.
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; Call the module constructors.
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ldx moveinit
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beq L0
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jsr initlib
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; Move the INIT segment from where it was loaded (over ZPSAVE and BSS)
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; into where it must be run (in the heap).
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; Push the command-line arguments; and, call main().
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jsr move_init
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dec moveinit ; set to false
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jsr callmain
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; Save space by putting the rest of the start-up code in the INIT segment,
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; which can be re-used by the heap.
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L0: jsr initstart
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; Back from main() [this is also the exit() entry]. Run the module destructors.
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@@ -98,14 +92,51 @@ L2: lda zpsave,x
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rts
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; ------------------------------------------------------------------------
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.segment "INIT"
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initstart:
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; Save the zero-page locations that we need.
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ldx #zpspace-1
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L1: lda sp,x
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sta zpsave,x
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dex
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bpl L1
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; Clear the BSS data.
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jsr zerobss
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; Set up the stack.
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lda #<__HIMEM__
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ldx #>__HIMEM__
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sta sp
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stx sp+1 ; Set argument stack ptr
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; Call the module constructors.
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jsr initlib
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; Push the command-line arguments; and, call main().
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jmp callmain
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; ------------------------------------------------------------------------
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; Data
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.data
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mmusave:.res 1
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spsave: .res 1
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moveinit:
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.byte 1
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.segment "ZPSAVE"
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zpsave: .res zpspace
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.bss
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spsave: .res 1
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mmusave:.res 1
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54
libsrc/common/moveinit.s
Normal file
54
libsrc/common/moveinit.s
Normal file
@@ -0,0 +1,54 @@
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;
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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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