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iigs-game-engine
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Refine the horizontal dispatch 

Find small optimizations to improve the average performance of the
blitter, especially in the odd-aligned case.

 - Odd-aligned PEA exit is 2 cycles faster per line
 - Odd-aligned JMP exit is 2 cycles faster per line
 - Odd-aligned LDA exit is 6 cycles faster (eliminated long store)
 - Merged setting the entry opcode and offset to convert 2 8-bit
   store into a single 16-bit store (save 6 cycles per line)
 - Load and save the full word for the high bytes. Cost 2 cycles
   but enabled the 6 cycles saved for the LDA case.
This commit is contained in:
Lucas Scharenbroich 2023-03-07 17:32:46 -06:00
parent 594b36a953
commit 536959619f
4 changed files with 441 additions and 67 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
src/Defs.s
View File

@ -292,6 +292,7 @@ _DirectListCount EXT
_DirectListTop EXT
_DirectListBottom EXT
StartXMod164Tbl EXT
; Tool error codes
NO_TIMERS_AVAILABLE equ 10

465
src/blitter/Horz.s
View File

@ -2,6 +2,35 @@
; these routines are to adjust tables and patch in new values into the code field
; when the virtual X-position of the play field changes.
; NOTE: There is still quite a bit of work done in the blitter to figure out if an
; opcode is a PEA, LDA or JMP. If there _some_ way that we could engineer a single
; target opcode change that would allow us to take different code branches in the
; blitter based on the opcode since the save/restore code has a change to look
; at the opcode now; before the blitter executes.
;
; PEA = $F4 = %1111 0100
; LDA (),y = $B1 = %1011 0001
; LDA 0,x = $B5 = %1011 0101
; JMP addr = $4C = %0100 1100
;
; IDEA: Save the 2-byte code directly after a BRA opcode to unconditionally branch out after masking. Would be a
; bit tricky to handle the forward and backward branches.
;
; Improvement. The current "fast path" for the PEA operand is
;
; ldal l_is_jmp+1-base ; 6
; bit #$000B ; 3
; bne :chk_jmp ; 2
; sep #$20 ; 3
; ldal l_is_jmp+3-base ; 5
; pha ; 3 = 22 cycles
;
; If we do an immediate branch to a routine that we _know_ is the right one, the code reduces to
;
; bra pea ; 3
; sep #$20 ; 3
; ldal l_is_jmp+3-base ; 5
; pha ; 3 = 17 cycles
; Simple function that restores the saved opcode that are stashed in _applyBG0Xpos. It is
; very important that opcodes are restored before new ones are inserted, because there is
@ -244,34 +273,39 @@ _ApplyBG0XPos
cmp #164 ; Keep the value in range
bcc *+5
sbc #164
:hop2
; Same logic as above. If the right edge is odd, then the full word needs to be drawn and we
; will enter at that index, rounded down.
;
; If the right edge is even, then only the low byte needs to be drawn, which is handled before
; entering the code field. So enter one word before the right edge.
;
; We performan an optimization here and fuse the entry_offset byte with the opcode that is
; changed depending on even/odd alignment in order to do the work with a single 16-bit
; store instead of two 8-bit stores.
bit #$0001
beq :odd_entry
and #$FFFE
tax
lda Col2CodeOffset,x
sta :entry_offset
lda #$004C ; set the entry_jmp opcode to JMP
lda Col2CodeOffset-1,x ; Only use the one byte for the entry_offset
and #$FF00
ora #$004C ; Merge in the JMP instruction
sta :opcode
stz :odd_entry_offset ; mark as an even case
bra :prep_complete
:odd_entry
tax
lda Col2CodeOffset,x
sta :entry_offset ; Will be used to load the data
lda Col2CodeOffset-1,x
and #$FF00
ora #$00AF
sta :opcode
lda Col2CodeOffset-2,x
sta :odd_entry_offset ; will the the actual location to jump to
lda #$00AF ; set the entry_jmp opcode to LDAL
sta :opcode
:prep_complete
; Main loop that
@ -286,26 +320,28 @@ _ApplyBG0XPos
:loop
ldx :virt_line_x2
ldal BTableLow,x ; Get the address of the first code field line
tay ; Save it to use as the base address
clc
adc :exit_offset ; Add some offsets to get the base address in the code field line
sta :exit_address
sty :base_address
ldal BTableHigh,x
ldal BTableHigh,x ; Get the bank
pha
plb
txa
ldal BTableLow,x ; Get the address of the first code field line
tay ; Save it to use as the base address
txa ; Calculate number of lines to draw on this iteration
and #$001E
eor #$FFFF
sec
adc #32
min :lines_left_x2
sta :draw_count_x2
tax ; Use for the first iteration
tya
clc
adc :exit_offset ; Add some offsets to get the base address in the code field line
sta :exit_address
sty :base_address
; First step is to set the BRA instruction to exit the code field at the proper location. There
; are two sub-steps to do here; we need to save the 16-bit value that exists at the location and
@ -315,12 +351,8 @@ _ApplyBG0XPos
; used in odd-aligned cases to determine how to draw the 8-bit value on the left edge of the
; screen
; y is already set to :base_address
tax ; :draw_count_x2
clc ; advance to the virtual line after the segment we just
adc :virt_line_x2 ; filled in
sta :virt_line_x2
lda :exit_address ; Save from this location (not needed in fast mode)
; ldx :draw_count_x2 ; :draw_count_x2
; lda :exit_address ; Save from this location (not needed in fast mode)
SaveOpcode ; X = :exit_address on return
txy ; ldy :exit_address -- starting at this address
@ -330,15 +362,10 @@ _ApplyBG0XPos
; Next, patch in the CODE_ENTRY value, which is the low byte of a JMP instruction. This is an
; 8-bit operation and, since the PEA code is bank aligned, we use the entry_offset value directly
;
; Now, patch in the opcode + code entry_offset
sep #$20
lda :entry_offset
ldy :base_address
SetCodeEntry ; All registers are preserved
; Now, patch in the opcode
lda :opcode
SetCodeEntryOpcode ; All registers are preserved
@ -347,15 +374,22 @@ _ApplyBG0XPos
lda :odd_entry_offset
jeq :not_odd
sep #$20
SetOddCodeEntry ; All registers are preserved
rep #$20
SaveHighOperand :exit_address ; Only used once, so "inline" it
:not_odd
rep #$21 ; clear the carry
; Do the end of the loop -- update the virtual line counter and reduce the number
; of lines left to render
clc
lda :virt_line_x2 ; advance to the virtual line after
adc :draw_count_x2 ; filled in
sta :virt_line_x2
lda :lines_left_x2 ; subtract the number of lines we just completed
sec
sbc :draw_count_x2
@ -368,6 +402,341 @@ _ApplyBG0XPos
plb
rts
; This is a variant of the above routine that allows each x-position to be set independently from a table of value. This is
; quite a bit slower than the other routine since we cannot store constant values for each line.
;
; We still want to perform operation in blocks of 16 to avoid repeatedly setting the data bank register for each line. In
; order to accomplish this, the even/odd cases are split into separate code blocks and the unrolled loop will patch up
; all of the memory locations on each line, rather than doing each patch one at a time. This may actually be more efficient
; since it eliminates several jmp (abs,x) / tax instructions and removed some register reloading.
;
; The two unrolled loop elements are:
;
; Even:
; lda: $0000,x ; Load from BTableLow + exit_offset
; sta: OPCODE_SAVE,y ; Save the two byte in another area of the line code
; lda :exit_bra
; sta $0000,x ; Replace the two bytes with a BRA instruction to exit the blitter
; lda :opcode|:entry_offset
; sta: CODE_ENTRY_OPCODE,y ; CODE_ENTRY_OPCODE and CODE_ENTRY are adjacent -- could make this a single 16-bit store
;
; Odd:
; Same as above, plus...
; lda :odd_entry_offset ; Get back into the code after fixing up the odd edge
; sta: ODD_ENTRY,y
; lda: $0002,x ; Save the high byte in case the last instruction is PEA and we need to load the top byte
; sta: OPCODE_HIGH_SAVE,y
;
_ApplyBG0XPosPerScanline
:stk_save equ tmp0
:virt_line_x2 equ tmp1
:lines_left_x2 equ tmp2
:draw_count_x2 equ tmp3
:exit_offset equ tmp4
:entry_offset equ tmp5
:exit_bra equ tmp6
:exit_address equ tmp7
:base_address equ tmp8
:opcode equ tmp9
:odd_entry_offset equ tmp10
; If there are saved opcodes that have not been restored, do not run this routine
lda LastPatchOffset
beq :ok
rts
; In this routine, basically every horizontal parameter is based off of the :virt_line_x2 index
:ok
lda StartYMod208 ; This is the base line of the virtual screen
asl
sta :virt_line_x2 ; Keep track of it
lda ScreenHeight
asl
sta :lines_left_x2
; Sketch out the core structural elements of the loop + bank management
phb ; Save the existing bank
tsc
sta :stk_save
:loop
ldx :virt_line_x2
txa
and #$001E
eor #$FFFF
sec
adc #2*16 ; 2 * (16 - virt_line % 16). This get us aligned to 16-line boundaries
min :lines_left_x2 ; Make sure we handle cases where lines_left < aligned remainder
sta :draw_count_x2 ; We are drawing this many lines on this iteration starting at _virt_line_x2
ldal BTableHigh,x ; Set the bank
pha
plb
jsr :DoScanlineRange ; Patch in the code field for this range (Bank is set)
lda :draw_count_x2
clc ; advance to the virtual line after the segment we just
adc :virt_line_x2 ; filled in
sta :virt_line_x2
lda :lines_left_x2 ; subtract the number of lines we just completed
sec
sbc :draw_count_x2
sta :lines_left_x2
jne :loop
lda :stk_save
tcs
plb
rts
:DoScanlineRange
ldx :virt_line_x2
; First, calculate the exit point
ldal StartXMod164Tbl,x ; Get the origin for this line
bit #$0001
bne :is_odd ; Quickly switch to specialized even/odd routines
; This is an even-aligned line
dec ; Move to the previous address for entry (a - 1) % 164
dec ; Optimization: Coule eliminate this with a double-width tbale for CodeFieldEvenBRA
bpl *+5
lda #162
; and #$FFFE ; Must be even by construction
tay
lda CodeFieldEvenBRA,y
sta :exit_bra ; Store are exit_offset +
lda Col2CodeOffset,y
sta :exit_offset
tya
adc ScreenWidth
cmp #164 ; Keep the value in range
bcc *+5
sbc #164
tay
lda Col2CodeOffset,y
sta :entry_offset
; lda #$004C ; set the entry_jmp opcode to JMP
; sta :opcode
; stz :odd_entry_offset ; mark as an even case
ldal BTableLow,x ; Get the address of the code field line
tay ; Save it to use as the base address
clc
adc :exit_offset ; Add some offsets to get the base address in the code field line
tax
clc
; This is the core even patch loop. The y-register tracks the base address of the starting line. Set the x-register
; based on the per-line exit_offset and eveything else references other data
; tya
; adc :exit_offset+{]line*2}
; tax
; lda: {]line*$1000},x
; sta: OPCODE_SAVE+{]line*$1000},y
; lda :exit_bra+{]line*2} ; Copy this value into all of the lines
; sta: {]line*$1000},x
; lda :entry_offset+{]line*2} ; Pre-merged with the appropriate opcode + offset
; sta: CODE_ENTRY_OPCODE+{]line*$1000},y
bra :prep_complete
; This is an odd-aligned line
:is_odd
dec ; Remove the least-significant byte (must stay positive)
tay
lda CodeFieldOddBRA,y
sta :exit_bra
lda Col2CodeOffset,y
sta :exit_offset
tya
adc ScreenWidth
cmp #164 ; Keep the value in range
bcc *+5
sbc #164
tay
lda Col2CodeOffset,y
sta :entry_offset ; Will be used to load the data
lda Col2CodeOffset-2,y
sta :odd_entry_offset ; will be the actual location to jump to
lda #$00AF ; set the entry_jmp opcode to LDAL
sta :opcode
:prep_complete
ldal BTableLow,x ; Get the address of the code field line
tay ; Save it to use as the base address
clc
adc :exit_offset ; Add some offsets to get the base address in the code field line
; sta :exit_address
; sty :base_address
; ldy :base_address
; ldx :exit_address ; Save from this location (not needed in fast mode)
; SaveOpcode ; X = :exit_address on return
tax
lda: $0000,x
sta: OPCODE_SAVE+$0000,y
; txy ; ldy :exit_address -- starting at this address
; ldx :draw_count_x2 ; Do this many lines
lda :exit_bra ; Copy this value into all of the lines
; SetConst ; All registers are preserved
sta: $0000,x
; Next, patch in the CODE_ENTRY value, which is the low byte of a JMP instruction. This is an
; 8-bit operation and, since the PEA code is bank aligned, we use the entry_offset value directly
sep #$20
lda :entry_offset
; ldy :base_address
; SetCodeEntry ; All registers are preserved
sta: CODE_ENTRY+$0000,y
; Now, patch in the opcode
lda :opcode
; SetCodeEntryOpcode ; All registers are preserved
sta: CODE_ENTRY_OPCODE+$0000,y
; If this is an odd entry, also set the odd_entry low byte and save the operand high byte
lda :odd_entry_offset
jeq :not_odd
; SetOddCodeEntry ; All registers are preserved
sta: ODD_ENTRY+$0000,y
; SaveHighOperand :exit_address ; Only used once, so "inline" it
ldx :exit_address
lda: $0002,x
sta: OPCODE_HIGH_SAVE+$0000,y
:not_odd
rep #$21 ; clear the carry
lda :virt_line_x2 ; advance to the virtual line after
adc :draw_count_x2 ; filled in
sta :virt_line_x2
lda :lines_left_x2 ; subtract the number of lines we just completed
sec
sbc :draw_count_x2
sta :lines_left_x2
jne :loop
rts
; DoEvenRange
;
; Does all the core operations for an even range (16-bit accumulator and registers)
;
; X = number of lines * 2, 0 to 32
; Y = starting line * $1000
; A = code field location * $1000
DoEvenRange mac
asl ; mult the offset by 2 and clear the carry at the same time
adc #dispTbl
stal patch+1
patch jmp $0000
dispTbl jmp bottom
db 1
jmp x01
db 1
jmp x02
db 1
jmp x03
db 1
jmp x04
db 1
jmp x05
db 1
jmp x06
db 1
jmp x07
db 1
jmp x08
db 1
jmp x09
db 1
jmp x10
db 1
jmp x11
db 1
jmp x12
db 1
jmp x13
db 1
jmp x14
db 1
jmp x15
db 1
x16 tya
adc :exit_offset+$1E
tax
lda: $F000,x
sta: OPCODE_SAVE+$F000,y
lda :exit_bra+$1E
sta: $F000,x
lda :entry_offset+$1E ; Pre-merged with the appropriate opcode + offset
sta: CODE_ENTRY_OPCODE+$F000,y
x15 tya
adc :exit_offset+$1E
tax
lda: $E000,x
sta: OPCODE_SAVE+$E000,y
lda :exit_bra+$1C
sta: $E000,x
lda :entry_offset+$1C
sta: CODE_ENTRY_OPCODE+$E000,y
x14 lda $D002,x
sta OPCODE_HIGH_SAVE+$D000,y
x13 lda $C002,x
sta OPCODE_HIGH_SAVE+$C000,y
x12 lda $B002,x
sta OPCODE_HIGH_SAVE+$B000,y
x11 lda $A002,x
sta OPCODE_HIGH_SAVE+$A000,y
x10 lda $9002,x
sta OPCODE_HIGH_SAVE+$9000,y
x09 lda $8002,x
sta OPCODE_HIGH_SAVE+$8000,y
x08 lda $7002,x
sta OPCODE_HIGH_SAVE+$7000,y
x07 lda $6002,x
sta OPCODE_HIGH_SAVE+$6000,y
x06 lda $5002,x
sta OPCODE_HIGH_SAVE+$5000,y
x05 lda $4002,x
sta OPCODE_HIGH_SAVE+$4000,y
x04 lda $3002,x
sta OPCODE_HIGH_SAVE+$3000,y
x03 lda $2002,x
sta OPCODE_HIGH_SAVE+$2000,y
x02 lda $1002,x
sta OPCODE_HIGH_SAVE+$1000,y
x01 lda: $0002,x
sta: OPCODE_HIGH_SAVE+$0000,y
bottom <<<
; SaveHighOperand
;
; Save the high byte of the 3-byte code field instruction into the odd handler at the end
@ -415,37 +784,37 @@ do02 ldx ]1
do01 ldx ]1
bra x01
do16 ldx ]1
x16 lda $F002,x
x16 lda $F001,x
sta OPCODE_HIGH_SAVE+$F000,y
x15 lda $E002,x
x15 lda $E001,x
sta OPCODE_HIGH_SAVE+$E000,y
x14 lda $D002,x
x14 lda $D001,x
sta OPCODE_HIGH_SAVE+$D000,y
x13 lda $C002,x
x13 lda $C001,x
sta OPCODE_HIGH_SAVE+$C000,y
x12 lda $B002,x
x12 lda $B001,x
sta OPCODE_HIGH_SAVE+$B000,y
x11 lda $A002,x
x11 lda $A001,x
sta OPCODE_HIGH_SAVE+$A000,y
x10 lda $9002,x
x10 lda $9001,x
sta OPCODE_HIGH_SAVE+$9000,y
x09 lda $8002,x
x09 lda $8001,x
sta OPCODE_HIGH_SAVE+$8000,y
x08 lda $7002,x
x08 lda $7001,x
sta OPCODE_HIGH_SAVE+$7000,y
x07 lda $6002,x
x07 lda $6001,x
sta OPCODE_HIGH_SAVE+$6000,y
x06 lda $5002,x
x06 lda $5001,x
sta OPCODE_HIGH_SAVE+$5000,y
x05 lda $4002,x
x05 lda $4001,x
sta OPCODE_HIGH_SAVE+$4000,y
x04 lda $3002,x
x04 lda $3001,x
sta OPCODE_HIGH_SAVE+$3000,y
x03 lda $2002,x
x03 lda $2001,x
sta OPCODE_HIGH_SAVE+$2000,y
x02 lda $1002,x
x02 lda $1001,x
sta OPCODE_HIGH_SAVE+$1000,y
x01 lda: $0002,x
x01 lda: $0001,x
sta: OPCODE_HIGH_SAVE+$0000,y
bottom <<<

39
src/blitter/Template.s
View File

@ -18,8 +18,8 @@ ODD_ENTRY equ odd_entry-base+1
CODE_TOP equ loop-base
CODE_LEN equ top-base
CODE_EXIT equ even_exit-base
OPCODE_SAVE equ odd_save-base ; spot to save the code field opcode when patching exit BRA
OPCODE_HIGH_SAVE equ odd_save-base+2 ; save the third byte
OPCODE_SAVE equ odd_low_save-base ; spot to save the code field opcode when patching exit BRA
OPCODE_HIGH_SAVE equ odd_high_save-base ; save the second and third byte
FULL_RETURN equ full_return-base ; offset that returns from the blitter
ENABLE_INT equ enable_int-base ; offset that re-enable interrupts and continues
LINES_PER_BANK equ 16
@ -37,7 +37,7 @@ PagePatches da {long_0-base+2}
da {long_1-base+2}
da {long_2-base+2}
da {long_3-base+2}
da {long_4-base+2}
; da {long_4-base+2}
da {long_5-base+2}
da {long_6-base+2}
da {odd_entry-base+2}
@ -62,7 +62,7 @@ BankPatches da {long_0-base+3}
da {long_1-base+3}
da {long_2-base+3}
da {long_3-base+3}
da {long_4-base+3}
; da {long_4-base+3}
da {long_5-base+3}
da {long_6-base+3}
BankPatchNum equ *-BankPatches
@ -178,38 +178,39 @@ loop lup 82 ; +6 Set up 82 PEA instruc
loop_back jmp loop-base ; +252 Ensure execution continues to loop around
loop_exit_3 jmp even_exit-base ; +255
long_5
odd_exit ldal l_is_jmp+1-base
bit #$000B
odd_exit sep #$21 ; 8-bit mode and set the carry just in case we get to a snippet JMP
long_5 ldal OPCODE_SAVE ; Load the opcode that was saved
bit #$0B
bne :chk_jmp
sep #$20
long_6 ldal l_is_jmp+3-base ; get the high byte of the PEA operand
long_6 ldal OPCODE_HIGH_SAVE+1 ; get the high byte of the PEA operand
; Fall-through when we have to push a byte on the left edge. Must be 8-bit on entry. Optimized
; for the PEA $0000 case -- only 19 cycles to handle the edge, so pretty good
:left_byte
; for the PEA $0000 case -- only 17 cycles to handle the edge, so pretty good
pha
rep #$20
rep #$21
; JMP opcode = $4C, JML opcode = $5C
even_exit jmp $1000 ; Jump to the next line.
ds 1 ; space so that the last line in a bank can be patched into a JML
:chk_jmp
bit #$0040
:chk_jmp mx %10 ; 8-bit accumulator / 16-bit registers
bit #$40
bne l_is_jmp
long_4 stal *+4-base
dfb $00,$00
rep #$20 ; saved 3 cycles using 8-bit mode, but give it back here.
odd_low_save dfb $00,$00 ; save the first and second bytes of the code field. Works for LDA dp,x and LDA (0),y
l_jmp_rtn xba
sep #$20
pha
rep #$61 ; Clear everything C, V and M
bra even_exit
l_is_jmp sec ; Set the C flag (V is always cleared at this point) which tells a snippet to push only the high byte
odd_save dfb $00,$00,$00 ; The odd exit 3-byte sequence is always stashed here
l_is_jmp
rep #$20 ; Back to 16-bit mode (carry was set above)
; sec ; Set the C flag (V is always cleared at this point) which tells a snippet to push only the high byte
dfb $4C ; Expect a JMP instruction
odd_high_save dfb $00,$00 ; The high 2 bytes of the 3-byte code field sequence is always stashed here
; Special epilogue: skip a number of bytes and jump back into the code field. This is useful for
; large, floating panels in the attract mode of a game, or to overlay solid

3
src/static/TileStore.s
View File

@ -382,6 +382,9 @@ BG1YOffsetTable ENT
; dw 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
--^
; Per-scanline offsets for BG0
StartXMod164Tbl ENT
; Other Toolset variables
OneSecondCounter ENT
dw 0