********************************************************* * * * Copyright (c) 1989, David Kinzer, All Rights Reserved * * * * Permission hereby granted to redistribute this * * program in unmodified form in a not for profit manner.* * * * Permission hereby granted to use this software freely * * in programs, commercial or not. * * * ********************************************************* * * * VBRtn.a * * * * Vertical Blanking Routine for analog joystick support.* * This routine reads the joyport hardware during every * * vertical blanking interrupt and stores the joystick * * data for use by the read routine. * * * ********************************************************* * The ordering of the buttons is sortof taken from the * RKM hardware manual (buttons 3 and 4 are not defined * there) * * when reading from the joyport it is xxxxxx13xxxxxx24 * where 1 & 2 are obtained directly, 3 is obtained by 1 * eor 3, and 4 is obtained by 2 eor 4. * * * Lattice (tm) users need to remove the comment asterisk * from the following line to make the assembler happy * csect text regbase equ $DFF000 joy0dat equ $00A pot0dat equ $012 joy1dat equ $00C pot1dat equ $014 WritePotgo equ -$12 o_U0X equ $0 offsets for data passing o_U0Y equ $2 structure o_U0b1 equ $4 o_U0b2 equ $5 o_U0b3 equ $6 o_U0b4 equ $7 o_U0eb1 equ $8 o_U0eb2 equ $9 o_U0eb3 equ $a o_U0eb4 equ $b o_U1X equ $c o_U1Y equ $e o_U1b1 equ $10 o_U1b2 equ $11 o_U1b3 equ $12 o_U1b4 equ $13 o_U1eb1 equ $14 o_U1eb2 equ $15 o_U1eb3 equ $16 o_U1eb4 equ $17 o_Potbase equ $18 o_flags equ $1c xdef _vbserver * We rely on the data area being pointed to by A1 upon * entry, which the exec does for us. * * We can consider D0, D1, A0, A1, A4, A5 and A6 scratch _vbserver: move.l #regbase,A0 A0 points to hardware base btst #0,o_flags+3(A1) see if unit 0 open * (btst works on bytes) beq u1 branch if not move.w pot0dat(A0),D0 save pot data move.w D0,D1 asl.w #8,D0 move.w D0,o_U0X(A1) and.w #$FF00,D1 move.w D1,o_U0Y(A1) move.w joy0dat(A0),D1 get joystick button * positions move.b o_U0b1(A1),D0 do button 1 * save previous state btst #9,D1 test to see if pressed sne o_U0b1(A1) set or clear data element * based on position beq.s u0t1 if not pressed we are done tst.b D0 was it pressed before? bne.s u0t1 yes, branch st o_U0eb1(A1) just pressed, set flag * indicating button pressed u0t1 move.b o_U0b2(A1),D0 do button 2 btst #2,D1 sne o_U0b2(A1) beq.s u0t2 tst.b D0 bne.s u0t2 st o_U0eb2(A1) u0t2 * The fastest way to do the exclusive or in this case is * to add 1 to the least significant bit. If that bit is * a 1, there will be a carry into the next position. If * so, and the next position is a zero, the result will be * a one. If the next position is a one, the result is a * zero. Obscure, but fast. Note that this renders all * other bits useless. We use a byte add here to prevent * ruining the button 2 and 4 data in the upper byte. add.b #1,D1 do button 3 move.b o_U0b3(A1),D0 btst #1,D1 sne o_U0b3(A1) beq.s u0t3 tst.b D0 bne.s u0t3 st o_U0eb3(A1) u0t3 add.w #$100,D1 do button 4 move.b o_U0b4(A1),D0 (same eor scheme used) btst #9,D1 sne o_U0b4(A1) beq.s u0t4 tst.b D0 bne.s u0t4 st o_U0eb4(A1) u0t4 u1 btst #1,o_flags+3(A1) see if unit 1 open beq restart move.w pot1dat(A0),D0 save pot data move.w D0,D1 asl.w #8,D0 move.w D0,o_U1X(A1) and.w #$FF00,D1 move.w D1,o_U1Y(A1) move.w joy1dat(A0),D1 get joystick button * positions move.b o_U1b1(A1),D0 do button 1 btst #9,D1 sne o_U1b1(A1) beq.s u1t1 tst.b D0 bne.s u1t1 st o_U1eb1(A1) u1t1 move.b o_U1b2(A1),D0 do button 2 btst #1,D1 sne o_U1b2(A1) beq.s u1t2 tst.b D0 bne.s u1t2 st o_U1eb2(A1) u1t2 add.b #1,D1 move.b o_U1b4(A1),D0 do button 4 btst #1,D1 sne o_U1b4(A1) beq.s u1t4 tst.b D0 bne.s u1t4 st o_U1eb4(A1) u1t4 add.w #$100,D1 do button 3 move.b o_U1b3(A1),D0 btst #9,D1 sne o_U1b3(A1) beq.s u1t3 tst.b D0 bne.s u1t3 st o_U1eb3(A1) u1t3 restart move.l #1,D0 move.l D0,D1 move.l o_Potbase(A1),A6 Call WritePotgo jsr WritePotgo(A6) move.l #0,D0 rts end * End: VBRtn.a