initial commit

atari800/util/atari/t7.asm

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+.include equates.m65
+*=  $0600
+PHA 
+TXA 
+PHA 
+TYA 
+PHA 
+LDA 1536
+STA WSYNC
+;
+STA WSYNC
+STA WSYNC
+STA WSYNC
+STA WSYNC
+STA WSYNC
+STA WSYNC
+STA WSYNC
+LDY RANDOM ;sta $D20B ;POTGO
+STA WSYNC
+;NOP
+;NOP
+;NOP
+;NOP
+;NOP
+;NOP
+;NOP
+;LDX 203
+;
+;STA COLPF0+2
+.byte 99 ;change this to -1 in the data statements 
+LDA RANDOM;LDA $D207 ;POT7
+STA 207
+;STA 204
+LDA VCOUNT
+STA 205
+STY 206 ;save old random
+LDA 208 ;disable dli flag
+CMP #$0
+BEQ SKIP
+LDA #64
+STA NMIEN
+SKIP sta wsync
+sta wsync
+lda 1537
+sta HPOSP0
+lda 1538
+sta SIZEP0
+lda 1539
+sta GRAFP0
+PLA
+TAY 
+PLA 
+TAX 
+PLA 
+RTI 
+;jmp SKIP2
+;REG
+;.dbyte $0001
+;SKIP2
+;LDA REG
+;ror a
+;STA REG
+
+
+

atari800/util/atari/t7.doc

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+T7.bas a test program for cycle-counting.
+The basic idea: we can find out how the real Atari does things by
+changing a register after a certain number of NOP's on a certain
+scanline.  By aligning a player with the colour change, the horizontal
+position can be determined and checked on the emulator.
+Second idea: We can use RANDOM as a cycle-timer.  Set the 9-bit
+random number generator (repeating 511 different values in a sequence),
+then generate all 511 values and store them in an array, with
+the value as the index and the index as the value.
+Then given two different readings of RANDOM at different times,
+look up the index of both in the table, and the difference , mod 511
+is the number of cycles elapsed between the readings.
+Only problem is that we can only read 8 bits of RANDOM, so there's
+two possible values for each reading, giving 4 possible offsets.
+But only one of these will remain constant if the procedure is
+repeated.
+The 4 values printed by the program at the bottom are the computed
+possible offsets, the one which remains constant is the acutal
+offset.
+
+N=# of NOP cycles
+P=HPOSP0
+C=register to change (0=player 0, 9=COLBK, 10=DMACTL, 11-13 HPOS,SIZE,GRAF)
+V=value to change to
+PG=player graphics
+M=antic IR mode
+
+