gson@niksula.hut.fi (Andreas Gustafsson) (10/07/90)
Due to popular demand, I'm posting the complete source code for the CHIP-48 video game interpreter to comp.sys.handhelds. I hope this will inspire others to write more free machine code software for the HP48SX. The intention of this posting is not that people should actually assemble the code; it's much easier to get the binary which was posted recently and is also available by FTP from vega.hut.fi as /pub/misc/hp48sx/asap/chip48-2.25-bin.Z. Rather, it should serve as a source of programming tips for those writing their own machine code programs. This source is written for the ASAP assembler, version 1.01. ASAP is also FTP:able from vega.hut.fi. To run the assembler, you need a 32-bit Unix machine and Perl 3.0 which is available from most major Unix archive sites. Here it is. Enjoy! ================================ Cut here ================================ ; @(#) chip.asap 2.25 9/15/90 ; ; chip.asap -- a CHIP-8 interpreter for the HP48SX ; ; (C) Copyright 1990 Andreas Gustafsson ; ; Noncommercial distribution allowed, provided that this ; copyright message is preserved, and any modified versions ; are clearly marked as such. ; ; The program makes use of undocumented low-level features of ; the HP48SX calculator, and may or may not cause loss of data, ; excessive battery drainage, and/or damage to the calculator ; hardware. The Author takes no responsibility whatsoever for ; any damage caused by the use of this program. ; ; THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR ; IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED ; WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. ; ; ; Register usage: ; ; d0 = general pointing ; d1 = points to chip-8 instruction (physical) ; ; r0 = CHIP-8 I register ; r1 = last time value ; r2 = physical address of virtual zero ; r3 = CHIP-8 PC ; ; standard preamble for Kermit download data.b 'H' data.b 'P' data.b 'H' data.b 'P' data.b '4' data.b '8' data.b '-' data.b 'A' data.a #2dcc ; machine code object begin: data.a end-begin ; length of object ; end of preamble ; HP48SX ROM locations ; These are for the Revision A ROM, they may need to be changed for ; other revisions. flush_kbd=#00d57 ; flush keyboard buffer do_in_c=#01160 ; perform "in.4 c" instruction alloc_str=#05b7d ; allocate string push_r0_shortint=#06537 ; push r0 as short integer, restore regs save_rpl_regs=#0679b ; save d0, d1, b, d restore_rpl_regs=#067d2 ; restore d0, d1, b, d check_1_arg=#18abf ; make sure stack isn't empty ; HP48SX RAM locations crcval=#00104 ; hardware CRC register hwtimer=#00138 ; hardware timer stackdisp_ptr=#7055B ; contains address of stack display menudisp_ptr=#70551 ; contains address of menu display flags_37=#706ce ; flags -37 to -40 ; data area layout (with a smarter assembler these offsets could be ; calculated automatically). ; Don't rearrange; in particular, the variables must be first and ; the order of the "V10".."V15" pseudovariables is important. ofs_vars=0 ; CHIP-8 variables, 16 vars * 2 nibbles = 32 ofs_timer=32 ; delay timer "V10", size = 2 ofs_sound=34 ; sound timer "V11", size = 2 ofs_sndon=36 ; sound on/off flag "V12.0", size = 1 ofs_sdata=37 ; speaker data "V12.1", "V13", size = 3 ofs_ckeys=40 ; control key status "V14-15", size=4 ofs_csp=44 ; CHIP-8 stack pointer, size 5 ofs_cstack=49 ; CHIP-8 stack, size "stacknibbles" = 64 ofs_linetab=113 ; display row table, size 64 * 5 = 320 ofs_regsave=433 ; r0..r3 temporary save location, size = 20 ofs_end=453 ; end of data area ; don't change these without updating the offsets above also stacklevels=16 ; size of CHIP-8 stack stacknibbles=64 ; 4*stacklevels ; execution begins here call.a check_1_arg ; check that stack is not empty call.a save_rpl_regs ; call ROM routine to save d0, d1, b, d ; if flag -40 (clock display) is set, clear it and exit. ; This is because the clock display interrupt (or whatever) ; causes problems, and doesn't get turned off just by clearing ; the flag. However, it does get turned off when the screen is ; redrawn after we exit, so the next time this program is started ; it will run normally. move.p5 flags_37,c move.a c,d0 ; point to flags -37..-40 move.p @d0,a ; get old flags brbc 3,a,noclock ; jump if flag -40 clear clrb 3,a ; clear flag -40 move.p a,@d0 ; store updated flags jump.3 exit ; don't continue just yet noclock: ; allocate a string for temporary data storage clrb #a,st ; no garbage collection done move.p5 ofs_end,c ; size of uninitialized data area call.a alloc_str ; call ROM routine to allocate a string swap.a c,d0 move.a c,r4 ; now R4 points to the string ; clear the CHIP-8 variables and initialize some pseudovariables move.a c,d0 ; point to variables (uses c value set above) clr.w c move.w c,@d0 ; clear V0..V7 add.a 16,d0 move.w c,@d0 ; clear V8..VF add.a 16,d0 move.p8 #40010000,c ; set timers to #00, sndon to #1, ; and sdata to #400 move.8 c,@d0 ; fill "linetab" with pointers to the display rows move.a r4,a ; get start of data area move.p5 ofs_linetab,c add.a a,c move.a c,d0 ; d0 points to linetab move.p5 stackdisp_ptr,c ; pointer to address of stack display move.p2 56,a ; 56 rows call.3 ltfill move.p5 menudisp_ptr,c ; pointer to address of menu display move.p2 8,a ; 8 rows call.3 ltfill ; allocate a 4 kB string for the CHIP-8 virtual memory clrb #a,st ; no garbage collection done move.p5 #2000,c ; 4 kB in nibbles call.a alloc_str ; call ROM routine to allocate a string ; now r0 points to the header of the newly allocated string ; object, and d0 points to the data part swap.a d0,c move.a c,r2 ; virtual zero in r2 ; hate nondeterministic bugs... clr.w a clr.w b clr.w c clr.w d chipmain: ; copy the chip-8 program from the argument string to the virtual ; chip-8 memory move.a r2,a ; get virtual zero move.p5 #0400,c ; virtual #0200 bytes add.a a,c move.a c,d0 ; now d0 points to virtual 0200 move.a @d1,c ; point to the argument object move.a c,d1 ; (presumably a string) move.a @d1,a ; get the object type move.p5 #02a2c,c ; string type prefix brne.a c,a,doerror ; exit if it isn't a string add.a 5,d1 ; skip the type move.a @d1,a ; get the object length sub.a 5,a ; subtract length of length move.p5 #01c00,c ; this is #1000 - #0200 bytes in nibbles brgt.a c,a,nottoolong doerror: jump.3 errexit ; string will not fit in 4 k nottoolong: add.a 5,d1 ; point to the object itself call.3 copynibbles ; pop the argument string off the stack call.a restore_rpl_regs add.a 5,d1 inc.a d call.a save_rpl_regs ; copy the hexadecimal character font to the virtual chip-8 memory, ; unpacking it on-the-fly move.a r2,c ; get virtual zero move.a c,d0 ; now d0 points to 0000 virtual move.a pc,a ref17: move.p5 hexfont-ref17,c add.a a,c move.a c,d1 ; now d1 points to the hex patterns move.p2 hexfontend-hexfont,a ; length (8 bits are enough) fontcopylo: move.1 @d1,c ; read a nibble sln.a c ; shift to high nibble in byte add.a 1,d1 move.2 c,@d0 ; store byte add.a 2,d0 dec.a a brnz.b a,fontcopylo intoff ; jump here when the "restart" key is pressed restart: ; initialize PC and I clr.a c move.a c,r0 ; I=0000 in r0 move.p3 #200,c ; relies on c being cleared move.a c,r3 ; PC=0200 in r3 ; initialize stack pointer move.a r4,a ; get start of data area move.p5 ofs_csp,c add.a a,c move.a c,d0 ; d0 now points to csp clr.a c move.a c,@d0 ; csp cleared call.3 i00e0 ; erase display ; initialize the time value clr.a c ; must clear all of c for comparison below move.p3 hwtimer,c move.a c,d0 ; point to hardware timer move.a @d0,c retry1: move.a c,a move.a @d0,c brne.a c,a,retry1 ; loop until we get same value twice move.p5 #00F80,a ; mask away 7 low bits of time value and.a a,c move.a a,r1 nextinstr: call.3 realtime ; do real-time chores brcc nocarry rtcarry: brbs 4,a,restart ; ENTER was pressed ; otherwise, the abort key was pressed; make a clean exit exit: call.a restore_rpl_regs move.a @d0,a ; dispatch next RPL instruction add.a 5,d0 jump.a @a nocarry: ; There appears to be some kind of interrupt that ; checks the keyboard status, and that doesn't get ; turned off by "intoff". Not knowing how to turn it off, we ; try to live with it by flushing the keyboard buffer ever so ; often, and trying to keep the "out" register zeroed most of ; the time (so that the keyboard will appear inactive when ; the interrupt checks it, even if keys really are being pressed). intoff ; just in case someone turned them on again call.a flush_kbd ; flush keyboard buffer (trashes d1 and c) dispatch: ; dispatch a CHIP-8 instruction move.a r3,c ; get cpc move.a c,a ; keep unincremented value add.a 2,a ; increment cpc by 2 bytes move.a a,r3 ; store incremented cpc call.3 virtophy ; unincremented value is in c move.a c,d1 ; store virtual pc in d1 clr.a c add.a 1,d1 ; point to MSN move.p @d1,c ; get MSN of first byte of CHIP-8 instruction sub.a 1,d1 ; back to beginning of instruction add.a c,c add.a c,c ; now c = nibble * 4 move.a pc,a ref6: add.a c,a move.p5 jumptab-ref6,c add.a a,c ; now c = jumptab + nibble * 4 move.a c,d0 clr.a c ; clear the 5th nibble move.4 @d0,c ; now c = jumptab entry move.a pc,a jtref: add.a c,a ; now a = jump address move.a pc,c retref: add.a retloc-retref,c push.a c ; push return address on stack jump.a a ; jump to instruction routine retloc: brcs errexit ; if carry is set, an error has occurred jump.3 nextinstr errexit: move.w r3,c ; get the current CHIP-8 PC value move.w c,r0 ; move to R0 call.a push_r0_shortint ; ROM routine: push short integer from R0 ; (this also restores saved d0, d1, b, d) call.a save_rpl_regs ; save the registers again (redundant?) jump.3 exit ; ltfill -- fill a part of "linetab" ltfill: move.a c,d1 move.a @d1,c ; get display address add.a 16,c ; increment past the GROB header (20 nibbles) add.a 4,c ltfill_loop: move.a c,@d0 add.a 16,c ; increment to next row (34 nibbles) add.a 16,c add.a 2,c add.a 5,d0 dec.b a brnz.b a,ltfill_loop ret ; copynibbles -- copy a memory block ; ; d1 points to source, d0 to destination, and ; a contains the number of nibbles to copy copynibbles: copylo: brz.a a,copyend move.1 @d1,c move.1 c,@d0 add.a 1,d0 add.a 1,d1 dec.a a jump.3 copylo copyend: ret ; realtime -- do various timer-driven real-time processing ; ; In: nothing ; Out: carry set iff real-time keypress detected; key code is in a ; Uses: all 16 nibbles of a and c; d0 ; but neither b nor d ; realtime: ; flip the speaker if the sound is on call.3 soundpd0 ; point to sound timer move.b @d0,c brz.b c,silent add.a 2,d0 ; point to sound on/off flag move.p @d0,c brz.p c,silent add.a 1,d0 ; point to speaker data move.3 @d0,c out.x c not.x c ; turn #400 into #800 and vice versa move.p3 #c00,a and.x a,c move.3 c,@d0 silent: ; check the hardware timer register to see if it is time for ; a 64 Hz realtime clock tick clr.a c ; must clear all of c for comparison below move.p3 hwtimer,c move.a c,d0 move.a @d0,c retry2: move.a c,a move.a @d0,c brne.a c,a,retry2 ; loop until we get same value twice move.p5 #00F80,a ; mask away 7 low bits of time value and.a a,c move.a r1,a ; now a is old value, c is new value brne.a c,a,dotick jump.3 notick ; code at notick depends on c.0 being zero dotick: ; handle a 64 Hz tick clr.a c ; decrement r1 by #80 move.p2 #80,c sub.a c,a move.p5 #00F80,c ; mask and.a c,a move.a a,r1 call.3 timerpd0 ; point to delay timer move.b @d0,c brz.b c,timerzero dec.b c move.b c,@d0 timerzero: add.a 2,d0 ; point to sound timer move.b @d0,c brz.b c,soundzero dec.b c move.b c,@d0 soundzero: ; check for various control keys call.3 ckeyspd0 ; point d0 to key status move.p3 #010,c ; row ENTER..backstep out.x c call.a do_in_c move.a c,a ; save "in" data in a clr.a c out.x c ; zero "out" port as fast as possible move.4 @d0,c ; get previous key status move.4 a,@d0 ; save current key status not.a a ; get keys that are not pressed and.a c,a ; ..but were.. retbs 4,a ; return with carry set if ENTER pressed retbs 0,a ; same for the backstep key brbs 3,a,togglesound ; +/- noabort: move.p1 #1,c ; set flag to indicate that a tick took place notick: retclrc ; return tick flag in c.0 ; toggle the sound flag (this is jumped to when the +/- key is pressed) togglesound: call.3 sndonpd0 move.p @d0,c not.a c move.p1 #1,a and.a a,c move.p c,@d0 jump.3 noabort ; nnnc - get NNN field of current instruction to c register ; ; In: d1 pointing to chip-8 instruction ; Out: NNN field of instruction in c (5 valid nibbles) ; Uses: none nnnc: clr.a c ; clear nibbles 3..4 move.1 2,p move.p @d1,c ; set nibble 2 move.1 0,p add.a 2,d1 ; point to second byte of instruction move.b @d1,c ; set nibbles 0 and 1 sub.a 2,d1 ; restore d1 ret ; virtophy -- convert virtual address to physical address ; ; In: virtual address in c ; Out: physical address in c ; Uses: a virtophy: add.a c,c ; convert bytes to nibbles move.a r2,a ; convert virtual to physical add.a a,c ret ; varpd0 - get pointer to variable to d0 ; ; In: d1 points to nibble containing variable number ; Out: d0 points to variable ; Uses: a,c varpd0: clr.a c move.p @d1,c ; get nibble with variable number cvarpd0: add.a c,c ; convert bytes to nibbles move.a r4,a add.a a,c move.a c,d0 ret ; var0pd0 -- load d0 with pointer to V0 ; ; In: none ; Out: d0 points to variable 0 ; Uses: a,c var0pd0: clr.a c move.p1 #0,c jump.3 cvarpd0 ; varfpd0 -- load d0 with pointer to VF ; ; In: none ; Out: d0 points to variable F ; Uses: a,c varfpd0: clr.a c move.p1 #f,c jump.3 cvarpd0 timerpd0: clr.a c move.p2 #10,c jump.3 cvarpd0 ; point d0 to timer soundpd0: clr.a c move.p2 #11,c jump.3 cvarpd0 ; point d0 to sound timer sndonpd0: clr.a c move.p2 #12,c jump.3 cvarpd0 ; point d0 to sound on/off flag ckeyspd0: clr.a c move.p2 #14,c jump.3 cvarpd0 ; point d0 to control key status ; varxcvarya -- get values of X and Y variables ; In: d1 points to instruction ; Out: c contains VX, zero padded to .a field ; a contains VY, zero padded to .a field ; Uses: d0 varxcvarya: call.3 varpd0 ; get pointer to X clr.a c move.b @d0,c ; get X value push.a c add.a 3,d1 ; point to Y nibble in instruction call.3 varpd0 ; get pointer to Y clr.a a move.b @d0,a ; get Y value pop.a c sub.a 3,d1 ; back to beginning of instruction ret ; In: d1 points to beginning instruction ; Out: c contains VX (5 nibbles valid) ; a contains VY (5 nibbles valid) ; d0 points to VX ; Uses: none alusetup: add.a 3,d1 ; point to Y nibble in instruction call.3 varpd0 sub.a 3,d1 clr.a c move.2 @d0,c ; VY in c push.a c call.3 varpd0 ; d0 is pointer to VX clr.a a move.2 @d0,a ; VX in a pop.a c ; VY in c swap.a a,c ; now VX in c and VY in a ret savecarry: srn.a c ; extract the carry byte srn.a c lsbcarry: move.p2 #01,a ; use low bit only and.b a,c push.a c call.3 varfpd0 ; get a pointer to VF pop.a c move.b c,@d0 ; store the carry byte retclrc ; testkey -- check whether a given hex key is pressed ; ; In: key number in c (5 low nibbles must be valid) ; Out: low nibble of c is nonzero iff key is pressed ; Uses: a,d0 testkey: add.a c,c ; index into keytab move.a pc,a ref16: add.a c,a move.p5 keytab-ref16,c add.a a,c move.a c,d0 ; now d0 points to keytab clr.a c move.1 @d0,c ; get "out" data out.x c call.a do_in_c move.a c,a ; store the input value in a clr.a c out.x c ; zero "out" port as fast as possible add.a 1,d0 move.1 @d0,c ; get "in" mask and.a a,c ret ; setup subroutine for fx55 or fx65 instruction ; ; In: d0 points to VX ; Out: d0 points to to V0, a points to VX, and d1 points to MI varcopysetup: swap.a c,d0 ; copy d0 to c move.a c,d0 push.a c ; save pointer to the last variable call.3 var0pd0 ; point d0 to first variable (v0) move.a r0,c ; get I call.3 virtophy move.a c,d1 ; point d1 to data at I pop.a c move.a c,a ; now a contains pointer to last var. ret i0: ; mcode call call.3 nnnc move.a c,a ; routine address is now in a clr.a c move.p2 #e0,c breq.a c,a,i00e0 move.p2 #ee,c breq.a c,a,i00ee retsetc ; illegal mcode call i00e0: ; erase screen move.a r4,a ; get start of data area move.p5 ofs_linetab,c add.a c,a ; a contains linetab pointer ; b counts down from 64 move.p2 64,c move.a c,b eraselo: move.a a,d0 move.a @d0,c move.a c,d0 ; d0 now points to display memory clr.w c move.w c,@d0 ; erase 16 nibbles add.a 16,d0 move.w c,@d0 ; and 16 more add.a 16,d0 move.b c,@d0 ; and 2 more, total 34 add.a 5,a dec.b b brnz.b b,eraselo retclrc i00ee: ; subroutine return move.a r4,a ; get start of data area move.p5 ofs_csp,c add.a a,c move.a c,d0 ; c and d0 both point to csp move.a @d0,a ; now a contains the chip-8 stack pointer (0..4n-4) retz.a a ; return with carry set if stack underflow sub.a 4,a ; drop one level move.a a,@d0 ; save new csp add.a 5,c ; point c at stack[0] add.a a,c ; point c at popped level move.a c,d0 ; point d0 at popped level clr.a c move.4 @d0,c move.a c,r3 ; set pc retclrc i1: ; 1NNN, jump dojmp: call.3 nnnc move.a c,r3 ; assign to pc retclrc i2: ; 2NNN, subroutine call move.a r4,a ; get start of data area move.p5 ofs_csp,c add.a a,c move.a c,d0 ; d0 and c both point to csp move.a @d0,a ; now a contains the chip-8 stack pointer (0..4n-4) ; c still points at csp add.a 5,c ; point c at stack[0] add.a a,c ; point c at first free stack level swap.a c,d0 ; now d0 points to free stack and c points to csp move.a r3,a ; get pc move.4 a,@d0 ; store pc in stack swap.a c,d0 ; now d0 points to cpc again move.a @d0,a ; now a contains the chip-8 stack pointer (0..4n-4) add.a 4,a move.p5 stacknibbles,c retlt.a c,a ; return with carry set if stack overflow move.a a,@d0 ; store incremented sp jump.3 dojmp ; the reset is like 1nnn i3: ; 3XKK, skip if X==KK call.3 varpd0 ; get pointer to X add.a 2,d1 ; point to second byte of instruction move.b @d1,a ; now a = KK move.b @d0,c ; now c = VX skipeq: brne.b c,a,noskip doskip: swap.a c,r3 ; increment cpc by 2 add.a 2,c swap.a c,r3 noskip: retclrc i4: ; 4XKK, skip if X<>KK call.3 varpd0 ; get pointer to X add.a 2,d1 ; point to second byte of instruction move.b @d1,a ; now a = KK move.b @d0,c ; now c = VX skipne: breq.b c,a,noskip jump.3 doskip i5: ; 5XY0, skip if X==Y call.3 varxcvarya ; get VX to c, VY to a jump.3 skipeq i9: ; 9XY0, skip if X!=Y call.3 varxcvarya ; get VX to c, VY to a jump.3 skipne i6: ; 6XKK, load variable by constant call.3 varpd0 ; get pointer to X add.a 2,d1 ; point to second byte of instruction move.b @d1,a ; now a = KK move.b a,@d0 ; store in variable retclrc i7: ; 7XKK, add constant to variable call.3 varpd0 ; get pointer to X add.a 2,d1 ; point to second byte of instruction move.b @d1,a ; now a = KK move.b @d0,c ; get old value add.b a,c ; add KK move.b c,@d0 ; store new value retclrc i8: ; arithmetic and logic operations add.a 2,d1 ; point to last nibble of instruction move.1 @d1,a sub.a 2,d1 move.p1 #0,c brne.p c,a,noti8xy0 i8xy0: ; VX := VY call.3 alusetup move.b a,@d0 ; store result retclrc noti8xy0: move.p1 #1,c brne.p c,a,noti8xy1 i8xy1: ; VX := VX or VY call.3 alusetup or.b a,c move.2 c,@d0 ; store result retclrc noti8xy1: move.p1 #2,c brne.p c,a,noti8xy2 i8xy2: ; VX := VX and VY call.3 alusetup and.b a,c move.2 c,@d0 ; store result retclrc noti8xy2: move.p1 #3,c brne.p c,a,noti8xy3 i8xy3: ; VX := VX xor VY call.3 alusetup move.b a,b or.b c,b ; (x or y) in b and.b a,c ; (x and y) in c not.b c and.b b,c ; (x xor y) in c move.b c,@d0 ; store result retclrc noti8xy3: move.p1 #4,c brne.p c,a,noti8xy4 i8xy4: ; VX := VX + VY; carry in VF call.3 alusetup add.a a,c move.2 c,@d0 jump.3 savecarry noti8xy4: move.p1 #5,c brne.p c,a,noti8xy5 i8xy5: ; VX := VX - VY; carry in VF call.3 alusetup subcommon: not.b a ; do monkey business to get inverted carry add.a a,c inc.a c move.2 c,@d0 jump.3 savecarry noti8xy5: move.p1 #6,c brne.p c,a,noti8xy6 i8xy6: ; VX := VX >> 1; carry in VF call.3 alusetup move.b c,a srb.b c move.2 c,@d0 ; store result move.b a,c ; use low bit of original byte for carry jump.3 lsbcarry noti8xy6: move.p1 #7,c brne.p c,a,noti8xy7 i8xy7: ; VX := VY - VX; carry in VF call.3 alusetup swap.a a,c jump.3 subcommon noti8xy7: move.p1 #e,c brne.p c,a,noti8xye i8xye: ; VX := VX << 1; carry in VF call.3 alusetup add.a c,c move.2 c,@d0 jump.3 savecarry noti8xye: retsetc ia: ; ANNN, set I call.3 nnnc move.a c,r0 ; assign to I retclrc ib: ; parametric jump to NNN+V0 call.3 varpd0 call.3 nnnc clr.a a move.b @d0,a add.a a,c move.a c,r3 ; assign to pc retclrc ic: ; pseudo-random number call.3 varpd0 ; now d0 points to VX move.p5 crcval,c swap.a c,d0 ; point d0 to hardware crc move.2 @d0,a ; read the low byte of the crc swap.a c,d0 ; now d0 points to VX again add.a 2,d1 ; point to second byte of instruction move.b @d1,c ; get mask sub.a 2,d1 ; restore d1 and.b a,c ; mask move.b c,@d0 ; store result retclrc id_abort: jump.3 fx0a_abort id: ; DXYN, show N-byte sprite at MI at screen coordinates (X,Y) ; I doesn't change ; synchronize with 64 Hz tick tickwait: call.3 realtime brcs id_abort ; a realtime key was pressed brz.p c,tickwait ; wait until a tick occus call.3 save_rregs ; save r0..r3 move.a r0,c ; get I call.3 virtophy move.a c,r0 ; now r0 points to sprite call.3 varxcvarya move.a c,d ; save X in d move.p2 #1f,c and.b c,a ; mask Y to range 0..31, leave in a move.p2 #3f,c and.b c,d ; mask X to range 0..63, save in d ; get the number of bytes in the sprite (preserving a and d) add.a 2,d1 ; point to N field clr.b c move.1 @d1,c add.b a,c ; now c contains Y + sprite length move.b c,b move.p2 #20,c sub.b c,b ; now b contains no. of overshoot lines brcc oshoot clr.b b ; no overshoot oshoot: clr.b c ; get sprite length again move.1 @d1,c sub.b b,c ; subtract overshoot move.1 c,0,p ; now p contains adjusted length move.1 p,c,15 ; byte counter in nibble 15 of c move.1 14,p clr.p c ; collision flag in nibble 14 of c move.1 0,p sub.a 2,d1 ; back to beginning of instruction call.3 sprite ; do it call.3 restore_rregs call.4 varfpd0 ; d0 points to VF clr.b c move.1 14,p brz.p c,nocolls inc.b c nocolls: move.b c,@d0 ; store collision flag move.1 0,p retclrc ; id ie: ; skip on key pressed / not pressed call.3 varpd0 clr.a c move.b @d0,c ; Telmac key number call.3 testkey clr.b d move.p c,d ; now d.b is nonzero iff key was pressed add.a 2,d1 ; point to second byte of instruction move.b @d1,a sub.a 2,d1 move.p2 #9e,c breq.b c,a,doex9e move.p2 #a1,c breq.b c,a,doexa1 retsetc doex9e: move.b d,c clr.b a jump.3 skipne ; skip iff d!=0 (key was pressed) doexa1: move.b d,c clr.b a jump.3 skipeq ; skip iff d==0 (key was not pressed) ; kwait -- wait for key, return it in low byte of c ; In: none ; Out: key code in low byte of c ; Uses: most everything except d0 ; ; The beep-and-wait-until-released behaviour may seem a bit crummy, ; but we're just trying to emulate the original Telmac PROM monitor ; keyboard input routine as closely as possible. kwait: swap.a c,d0 push.a c ; save d0 value clr.a d ; low nibble of d used for key code kwalo: move.a d,c call.3 testkey brnz.p c,pressed call.3 realtime ; preserves d brcs kwabort inc.p d ; loop through keys 0..15 jump.3 kwalo pressed: call.3 soundpd0 move.p2 #04,c move.2 c,@d0 ; set sound timer to #04 call.3 realtime ; make some noise brcs kwabort move.a d,c call.3 testkey brnz.p c,pressed ; wait until key is released pop.a c ; restore d0 value move.a c,d0 move.b d,c retclrc kwabort: pop.a c ; adjust stack retsetc if: ; misc. functions using VX ; d0 is set up to point to VX call.3 varpd0 add.a 2,d1 ; point to second byte of instruction move.b @d1,a sub.a 2,d1 move.p2 #07,c brne.b c,a,notifx07 ifx07: ; read timer swap.a c,d0 push.a c call.3 timerpd0 move.b @d0,a pop.a c swap.a c,d0 move.b a,@d0 retclrc notifx07: move.p2 #0a,c brne.b c,a,notifx0a ifx0a: call.3 kwait brcs fx0a_abort move.b c,@d0 retclrc fx0a_abort: pop.a c ; adjust stack for forced return jump.3 rtcarry notifx0a: move.p2 #15,c brne.b c,a,notifx15 ifx15: ; set timer move.b @d0,c push.a c call.3 timerpd0 pop.a c move.b c,@d0 retclrc notifx15: move.p2 #18,c brne.b c,a,notifx18 ifx18: ; set sound move.b @d0,c push.a c call.3 soundpd0 pop.a c move.b c,@d0 retclrc notifx18: move.p2 #1e,c brne.b c,a,notifx1e ifx1e: ; increment I by VX clr.a c move.b @d0,c move.a r0,a ; get old I add.x c,a ; increment, modifying only 3 low nibbles retcs ; it wrapped around #1000 move.a a,r0 ; save new I retclrc notifx1e: move.p2 #29,c brne.b c,a,notifx29 ifx29: ; point to hex display pattern ; assumes that the hex patterns are at virtual 0000 clr.a c move.1 @d0,c ; use low nibble of variable move.a c,a add.a c,c ; * 2 add.a c,c ; * 4 add.a a,c ; * 5 move.a c,r0 ; this is the new I retclrc notifx29: move.p2 #33,c breq.b c,a,ifx33 jump.3 notifx33 ifx33: ; 8-bit binary to decimal conversion move.b @d0,c move.b c,d ; d contains the byte to convert move.a pc,a ref12: move.p5 dectab-ref12,c add.a a,c move.a c,d0 ; d0 points to the conversion table clr.a a ; a accumulates decimal result cnvbit: brz.b d,cnvend move.b d,c brbc 0,c,skpbit ; jump if low-order bit is zero move.3 @d0,c setdec add.a c,a ; only 3 low nibbles contain real data sethex skpbit: add.a 3,d0 srb.b d jump.3 cnvbit cnvabort: retsetc cnvend: move.a a,b ; save the decimal value move.a r0,c ; get I move.p5 #00ffd,a ; is I > 0FFD hex? retgt.a c,a ; protect memory above 0FFF call.3 virtophy move.a c,d0 ; virtual I in d0 move.a b,a ; restore the decimal value clr.a c move.1 2,p move.p a,@d0 ; most significant digit first add.a 1,d0 move.p c,@d0 ; zero add.a 1,d0 move.1 1,p move.p a,@d0 ; middle digit add.a 1,d0 move.p c,@d0 ; zero add.a 1,d0 move.1 0,p move.p a,@d0 ; least significant digit add.a 1,d0 move.p c,@d0 ; zero ; I doesn't change retclrc notifx33: move.p2 #55,c brne.b c,a,notifx55 ifx55: ; save vars in memory call.3 varcopysetup savelo: move.b @d0,c ; read a byte from variable move.b c,@d1 ; store in MI swap.a c,d0 ; get d0 to c move.a c,d0 brge.a c,a,doret1 ; are we ready yet? add.a 2,d1 add.a 2,d0 move.a r0,c ; get I value inc.x c ; increment 3 low nibbles retcs ; if carry, we might overwrite #1000 move.a c,r0 ; I changes permanently jump.3 savelo doret1: retclrc notifx55: move.p2 #65,c brne.b c,a,notifx65 ifx65: ; restore vars from memory call.3 varcopysetup restolo: move.b @d1,c ; read a byte at MI move.b c,@d0 ; store in variable swap.a c,d0 ; get d0 to c move.a c,d0 brge.a c,a,doret1 ; are we ready yet? add.a 2,d1 add.a 2,d0 move.a r0,c ; get I value inc.x c ; increment 3 low nibbles retcs ; if carry, we wrapped around #1000 move.a c,r0 ; I changes permanently jump.3 restolo notifx65: ; unknown FxNN instruction retsetc ; save registers r0..r3 save_rregs: move.a r4,a ; get start of data area move.p5 ofs_regsave,c add.a a,c move.a c,d0 move.a r0,c move.a c,@d0 add.a 5,d0 move.a r1,c move.a c,@d0 add.a 5,d0 move.a r2,c move.a c,@d0 add.a 5,d0 move.a r3,c move.a c,@d0 add.a 5,d0 ret ; restore registers r0..r3 restore_rregs: move.a r4,a ; get start of data area move.p5 ofs_regsave,c add.a a,c move.a c,d0 move.a @d0,c move.a c,r0 add.a 5,d0 move.a @d0,c move.a c,r1 add.a 5,d0 move.a @d0,c move.a c,r2 add.a 5,d0 move.a @d0,c move.a c,r3 add.a 5,d0 ret ; sprite: draw a CHIP-8 "sprite", 8 pixels wide by 1..15 pixels high ; ; in: r0.a points to sprite data ; a.a contains x coordinate ; d.a contains y coordinate ; c.14 zero initial value for collision flag ; c.15 number of lines in sprite ; out: c.14 collision flag ; ; register usage: ; a,c used for scratch ; c.15 contains sprite byte (line) count ; c.14 contains collision flag ; c.13 is used as temporary save location for p ; c.12 is nonzero in "short mode" (2x1 pixels) ; b contains the byte to display ; d contains the 32-bit pixel string ; r0 points to sprite data ; r1 points to linetab ; r2 contains the X offset in nibbles from the beginning of the lcd line ; r3 contains entry point to pixel alignment shifts sprite: move.1 12,p move.p1 0,c ; set "short flag" move.1 0,p move.1 12,p brnz.p c,short1 ; "short mode"? add.a a,a ; 2Y (the chip-8 pixels are 2 lines high) short1: move.1 0,p ; (but not in "short mode" move.a a,c ; multiply by 5 to get index into linetab add.a a,a add.a a,a add.a a,c ; now c contains index to linetab move.a r4,a ; get start of data area add.a c,a move.p5 ofs_linetab,c add.a a,c move.a c,r1 ; r1 is the linetab pointer ; calculate X offset in nibbles from the beginning of the lcd line move.a d,c ; c = X srb.a c ; convert pixels to pixel octets srb.a c srb.a c add.a c,c ; convert pixel octets to nibbles add.a c,c move.a c,r2 ; r2 contains offset from beginning of line ; calculate entry point to alignment shifts move.p2 #07,c ; d should still contain X and.b c,d ; mask out 3 low bits add.a d,d ; the shift instructions are 2 nibbles each move.a pc,a ref11: move.p5 shifts-ref11,c add.a a,c add.a d,c move.a c,r3 ; r3 now contains entry point to shifts linelo: move.a r0,c ; get sprite pointer move.a c,d0 move.2 @d0,c ; byte to display clr.a b move.b c,b ; ..to low byte of b; next byte is clear swap.a c,d0 add.a 2,c ; advance to next sprite byte move.a c,r0 ; save sprite pointer ; the low byte of b now contains the sprite byte move.a r3,c ; get shift entry point jump.a c ; jump to the appropriate shift instruction shifts: add.a b,b ; two-nibble instructions add.a b,b add.a b,b add.a b,b add.a b,b add.a b,b add.a b,b add.a b,b move.a pc,a ref2: move.p5 pixtab-ref2,c add.a c,a ; beginning of pixtab is in a ; keep &pixtab[0] in a at all times clr.a c move.p b,c ; extract a nibble from b add.a c,c ; times two add.a a,c ; add beginning of pixtab move.a c,d0 ; point d0 to pixtab byte move.b @d0,c move.b c,d ; now 8 more pixels in d sln.w d sln.w d srn.a b clr.a c move.p b,c ; extract a nibble from b add.a c,c ; times two add.a a,c move.a c,d0 ; point d0 to pixtab byte move.b @d0,c move.b c,d ; now 8 more pixels in d sln.w d sln.w d srn.a b clr.a c move.p b,c ; extract a nibble from b add.a c,c ; times two add.a a,c move.a c,d0 ; point d0 to pixtab byte move.b @d0,c move.b c,d ; now 8 more pixels in d sln.w d sln.w d srn.a b clr.a c move.p b,c ; extract a nibble from b add.a c,c ; times two add.a a,c move.a c,d0 ; point d0 to pixtab byte move.b @d0,c move.b c,d ; now 8 more pixels in d ; now d contains 32 pixels move.a r1,a ; get linetab pointer move.a a,d0 ; ..to d0 move.a @d0,c ; address of current line to c move.1 12,p brnz.p c,short2 add.a 5,a ; point 1 line ahead if "short mode", short2: add.a 5,a ; point 2 lines ahead otherwise move.1 0,p move.a a,r1 ; this is the new linetab pointer move.a r2,a ; X offset in nibbles add.a a,c ; add beginning of lcd line move.a c,d0 ; now d0 points to display buffer ; now we operate on the display buffer with a word length ; that is normally 32 bits, but near the right end we ; must decrease it to avoid wrapping around and messing up ; the left part of the display. Therefore the word length ; should be min(8, 32-xoff) nibbles. move.p2 32,c sub.b a,c ; now c = 32-xoff move.p2 8,a brlt.b c,a,clip ; if (32-xoff) is < 8, use that, else 8 move.b a,c clip: dec.b c ; .wp field is (p+1) nibbles; compensate move.1 c,0,p ; set field size move.wp @d0,c ; get old display buffer contents move.wp c,a ; make a copy in a and.wp d,c ; now c = (old and new), a = old, d = new brz.wp c,nocoll ; there has been a collision; set nibble 14 in c swap.1 p,c,13 ; save p in nibble 13 of c move.1 14,p move.p1 1,c ; set collision flag in nibble 13 of c swap.1 p,c,13 ; restore p nocoll: swap.wp d,c ; now d = (old and new), a = old, c = new or.wp a,c ; now c = (old or new) not.wp d and.wp d,c ; now c = (old or new) and not(old and new) swap.1 p,c,13 move.1 12,p brnz.p c,short3 swap.1 p,c,13 move.wp c,@d0 ; store once add.a 16,d0 ; advance by 34 to next scan line add.a 16,d0 add.a 2,d0 move.wp c,@d0 ; store again jump.3 noshort3 short3: swap.1 p,c,13 move.wp c,@d0 ; store just once noshort3: move.1 0,p dec.s c brz.s c,lineexit jump.3 linelo lineexit: ret ; sprite ; this lookup table serves a dual purpose: it swaps the bits in a nibble ; to convert from big-endian to little-endian format, and doubles each bit ; to lower the resolution to 64 pixels horizontally. pixtab: data.b !00000000 data.b !11000000 data.b !00110000 data.b !11110000 data.b !00001100 data.b !11001100 data.b !00111100 data.b !11111100 data.b !00000011 data.b !11000011 data.b !00110011 data.b !11110011 data.b !00001111 data.b !11001111 data.b !00111111 data.b !11111111 ; 4x5 pixel hexadecimal character font patterns hexfont: data.5 #F999F data.5 #72262 data.5 #F8F1F data.5 #F1F1F data.5 #11F99 data.5 #F1F8F data.5 #F9F8F data.5 #4421F data.5 #F9F9F data.5 #F1F9F data.5 #99F9F data.5 #E9E9E data.5 #F888F data.5 #E999E data.5 #F8F8F data.5 #88F8F hexfontend: ; powers of two in BCD, for binary-to-decimal conversion dectab: data.3 #001 data.3 #002 data.3 #004 data.3 #008 data.3 #016 data.3 #032 data.3 #064 data.3 #128 ; table mapping Telmac hex key locations to HP48SX key codes ; lsn is bit mask to output, lsn is bit mask to mask input with keytab: data.2 #41 data.2 #88 data.2 #48 data.2 #28 data.2 #84 data.2 #44 data.2 #24 data.2 #82 data.2 #42 data.2 #22 data.2 #81 data.2 #21 data.2 #18 data.2 #14 data.2 #12 data.2 #11 ; jump table for CHIP-8 instruction dispatching based on the first nibble jumptab: data.4 i0-jtref data.4 i1-jtref data.4 i2-jtref data.4 i3-jtref data.4 i4-jtref data.4 i5-jtref data.4 i6-jtref data.4 i7-jtref data.4 i8-jtref data.4 i9-jtref data.4 ia-jtref data.4 ib-jtref data.4 ic-jtref data.4 id-jtref data.4 ie-jtref data.4 if-jtref regsave: even ; pad to even number of nibbles end: ; don't add stuff after this line. ================================ Cut here ================================ -- Andreas Gustafsson Internet: gson@niksula.hut.fi Voice: +358 0 563 5592