175 lines
3.1 KiB
ArmAsm
175 lines
3.1 KiB
ArmAsm
FR0 = $d4 ; float48
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PORTB = $d301
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EXTENDED_RAM = $4000 ; 16KiB bank on the XE
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; lookup table for top byte -> PORTB value for bank-switch
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.align 256
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bankswitch:
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.repeat 256, i
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.byte ((i & $c0) >> 5) | $c1
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.endrepeat
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; 58-77 cycles
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; clobbers x, y, dest to dest + 3
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.macro imul8xe dest, arg1, arg2
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.local done
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.local output
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.local ptr
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output = dest
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ptr = dest + 2 ; scratch space assumed
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; bottom 14 bits except the LSB are the per-bank table index
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; add $4000 for the bank pointer
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lda arg1 ; 3 cyc
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and #$fe ; 2 cyc
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sta ptr ; 3 cyc
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lda arg2 ; 3 cyc
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and #$3f ; 2 cyc
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clc ; 2 cyc
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adc #$40 ; 2 cyc
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sta ptr + 1 ; 3 cyc
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; top 2 bits are the table bank selector
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ldx arg2 ; 3 cyc
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lda bank_switch,x ; 4 cyc
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sta PORTB ; 4 cyc
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; copy the entry into output
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ldy #0 ; 2 cyc
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lda (ptr),y ; 5 cyc
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sta output ; 3 cyc
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iny ; 2 cyc
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lda (ptr),y ; 5 cyc
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sta output+1 ; 3 cyc
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; note: we are not restoring memory to save 6 cycles!
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; this means those 16kb have to be switched back to base RAM
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; if we need to use them anywhere else
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;;; restore memory
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;;lda #$81 ; 2 cyc - disabled
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;;sta PORTB ; 4 cyc - disabled
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; check that 1 bit we skipped to fit into space
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lda arg1 ; 3 cyc
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and #1 ; 2 cyc
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beq done ; 2 cyc
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; add the second param one last time for the skipped bit
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clc ; 2 cyc
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lda arg2 ; 3 cyc
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adc output ; 3 cyc
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sta output ; 3 cyc
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lda #0 ; 2 cyc
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adc output+1 ; 3 cyc
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sta output+1 ; 3 cyc
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done:
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.endmacro
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.macro bank_switch bank
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lda #((bank << 1) | $c1)
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sta PORTB
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.endmacro
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proc imul8xe_init
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; go through the input set, in four 16KB chunks
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arg1 = FR1
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arg2 = FR2
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result = FR0
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lda #$00
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sta arg1
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sta arg2
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; $00 * $00 -> $3f * $ff
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bank_switch 0
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jsr imul8xe_init_section
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; $40 * $00 -> $7f * $ff
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bank_switch 1
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jsr imul8xe_init_section
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; $80 * $00 -> $bf * $ff
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bank_switch 2
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jsr imul8xe_init_section
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; $c0 * $00 -> $ff * $ff
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bank_switch 3
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jsr imul8xe_init_section
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rts
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endproc
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; Initialize a 16 KB chunk of the table
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; input: multipliers in temp
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; output: new multipliers in temp
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; clobbers: temp, temp2
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proc imul8xe_init_section
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arg1 = FR1
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arg2 = FR2
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result = FR0
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ptr = temp2
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lda #$00
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sta ptr
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lda #$40
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sta ptr + 1
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ldx #0
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ldy #0
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; outer loop: $00 -> $3f
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outer_loop:
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; reset result to 0
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lda #0
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sta result
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sta result + 1
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; inner loop: $00 -> $ff
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inner_loop:
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; copy result to data set
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lda result
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sta (ptr),y
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lda result + 1
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sta (ptr),y
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; result += 2 * arg2
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clc
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lda arg2
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adc result
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sta result
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lda #0
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adc result + 1
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sta result
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lda arg2
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adc result
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sta result
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lda #0
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adc result + 1
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sta result
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; inner loop check
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inc arg1
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inc arg1
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inc ptr
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inc ptr
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bne inner_loop
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; outer loop check
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inc arg2
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inc ptr + 1
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lda ptr + 1
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cmp #$40
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bne outer_loop
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rts
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endproc
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