Fully flesh out Script execution implementation
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Lucas Scharenbroich
parent
740a0f260d
commit
23f7e5b0fb
130
src/Script.s
130
src/Script.s
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@ -29,57 +29,103 @@
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; A = low word of script command array
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; X = high word of script command array
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; Y = number of ticks between each command step
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;
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; A pointer to the current command instruction is stored in the first 4 bytes of the
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; timer's user data section.
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StartScript ENT
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phb
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phk
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plb
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phx ; Save the script array address
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phx ; Save the script array address
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pha
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lda #_DoScriptStep ; Try to create a timer for this script
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ldx #^_DoScriptStep
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lda #_DoScriptSeq ; Try to create a timer for this script
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ldx #^_DoScriptSeq
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clc
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jsl AddTimer
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bcs :err ; No timer slots available :(
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bcs :err ; No timer slots available :(
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tax ; Initialize the UeerData with the command array and PC
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tax ; Initialize the UserData with the command pointer
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pla
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sta Timers+8,x
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pla
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sta Timers+10,x
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stz Timers+12,x ; Index of the commands
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plb
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rtl
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:err
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pla ; Pop the values and return with the carry flag set
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pla ; Pop the values and return with the carry flag set
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pla
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plb
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rtl
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_DoScriptStep
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lda Timers+8,x
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lda Timers+10,x
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ldy Timers+12,y
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lda [CmdList],y
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pha ; save the full command word
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; This routine executes script command until it encounters one with the STOP bit set. In some
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; sense, the stop bit acts like a "yield" in high-levellanguages.
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_DoScriptSeq
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phx ; save the timer index; will need to update user data at the end
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phb ; save the current data bank
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and #$001E
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sep #$20 ; push the bank byte of the command list pointer on the stack
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lda Timers+10,x
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pha
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rep #$20
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lda Timers+8,x ; get the current address of the command sequence
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tax
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plb ; pop the bank
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; Now we are ready to process commands until reaching one with the STOP bit set. Each command
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; is 8 bytes, so we just have to do a very simple fetch/execute/increment loop. The only
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; exception is handling the JUMP bit which requires moving the script pc stored in the
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; x-register.
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:loop phx ; Save the command address
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lda: 0,x ; Load the command word
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pha ; Stash it
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and #$001E ; Only have 16 built-in command. Use the _UserCallback
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tax ; command for custom functionality
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jsr (:commands,x)
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pla ; restore the command word
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bit #$4000 ; If the branch bit is set, change the command pointer
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beq :no_jump
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lda 1,s ; Reload the command word
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; Move to the next instruction. If the JUMP bit is set, we move the address forward or
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; backward N commands (8 bytes at a time). If the JUMP bit is not set, then just move
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; to the next entry.
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bit #$4000 ; Just do a fall through and set the jump offset to
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bne :move_addr ; a hard-coded value of 1 if the jump bit is not set
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:retry lda #$0100
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:move_addr and #$0F00 ; mask out the number of commands to move
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beq :retry ; Don't allow zeros; will cause infinite loop. Just advance by one.
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xba ; put it in the low byte
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cmp #$0008 ; Sign-extend the 4-bit value
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bcc *+5
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ora #$FFF0
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asl ; multiply by 8
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asl
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asl
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clc
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adc 3,s ; add it to the saved command address
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sta 3,s
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; Check to see if we stop on this instruction, or continue executing commands
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pla ; Reload the command word
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plx ; Pop off the update command address
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bit #$8000 ; If the stop bit is set, we're done with this sequence
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beq :continue ; Otherwise, keep going and fetch the next command word
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txa ; save the current command address
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plb ; restore the data bank and the timer index
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plx
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sta Timers+8,x ; store the command address back into the timer user data space
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:no_jump
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bit #$8000 ; If the terminate bit is set, remove this handler
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beq :no_term
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txa
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jsl RemoveTimer
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:no_term
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rtl
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:commands dw _Null,_SetPalEntry,_SwapPalEntry,_Null,_Null,_Null,_Null,_Null
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@ -101,13 +147,13 @@ _SetPalEntry
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_SwapPalEntry txy
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ldx ARG1,y ; Load palette values
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ldx ARG1,y ; Load palette values
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ldal SHR_PALETTES,x
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pha
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ldx ARG2,y
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ldal SHR_PALETTES,x
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ldx ARG1,y ; and swap
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ldx ARG1,y ; and swap
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stal SHR_PALETTES,x
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ldx ARG2,y
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@ -142,6 +188,40 @@ _UserCallback lda ARG1,x
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