85 lines
1.6 KiB
ArmAsm
85 lines
1.6 KiB
ArmAsm
// #LAYOUT# STD * #TAKE
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// #LAYOUT# * BASIC_0 #TAKE
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// #LAYOUT# * * #IGNORE
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cmd_new:
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jsr basic_do_new
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// NEW command terminates execution
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// (Confirmed on a C64)
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jmp basic_main_loop
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cmd_clr:
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jsr basic_do_clr
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// CLR command does not stop execution
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// (Cconfirmed on a c64)
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jmp basic_execute_statement
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basic_do_new:
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// Setup pointers to memory storage XXX should depend on text start vector
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lda #<$0801
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sta TXTTAB+0
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lda #>$0801
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sta TXTTAB+1
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sta VARTAB+1
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lda #<$0803
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sta VARTAB+0
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// Zero line pointer
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// XXX - We should also zero $0800, i.e., TXTTAB - 1
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ldy #$00
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tya
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sta (TXTTAB),y
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iny
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sta (TXTTAB),y
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// Get top of memory.
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// If a cart is present, then it is $7FFF,
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// if not, then it is $F7FF, since we support having
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// programs and variables under ROM.
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// i.e., we support 56KB RAM for BASIC, keeping some space
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// free for some optimisation structures, e.g., FOR/NEXT loop
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// records (without them going on the stack), GOSUB stack
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// (same story), expression value cache?
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sec // Read, not write value
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jsr JMEMTOP
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cpx #$80
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beq !+
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#if CONFIG_MEMORY_MODEL_60K
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lda #>$F7FF
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#else // CONFIG_MEMORY_MODEL_38K
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lda #>$A000
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#endif
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.byte $2C
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!:
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#if CONFIG_MEMORY_MODEL_60K
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lda #>$F7FF
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#else // CONFIG_MEMORY_MODEL_38K
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lda #>$A000
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#endif
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sta MEMSIZ+1
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sta FRETOP+1
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#if CONFIG_MEMORY_MODEL_60K
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lda #<$F7FF
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#else // CONFIG_MEMORY_MODEL_38K
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lda #<$A000
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#endif
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sta MEMSIZ+0
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sta FRETOP+0
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// FALL THROUGH
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basic_do_clr:
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// Clear variables, arrays and strings
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lda VARTAB+0
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sta ARYTAB+0
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sta STREND+0
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lda VARTAB+1
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sta ARYTAB+1
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sta STREND+1
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rts
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