8-bit acorn software: other • Re: 6502 tube coding guidelines

Code:

   10 REM > OswDemo/src   20 REM Demonstrate adding an OSWORD via USERV   30 :   40 myOSW=&E0        :REM My OSWORD call number   50 USERV=&200       :REM Vector to user OSWORD routines   60 ctrl=&F0         :REM Points to the control block   70 load%=&FFFF2500  :REM We'll load to &2500 in the I/O processor   80 fname$="OswDEMO" :REM This is what we'll call it   90 DIM mcode% &100  :REM Some space to assemble the code  100 :  110 REM OSWORD control block standard layout  120 REM   XY?0 = number of parameter bytes  130 REM   XY?1 = number of result bytes  140 REM   XY?2 = conventionally command  150 REM   XY?3 = conventionally subcommand  160 REM   XY!4 onwards any other data  170 :  180 REM Call with code similar to:  190 REM DIM ctrl% 31:X%=ctrl%:Y%=X%DIV256  200 REM X%?0=4            :REM Size of outward control block  210 REM X%?1=32           :REM Size of returned control block  220 REM X%?2=6            :REM Let's do command 6  230 REM !X%=&62004        :REM Alternative way of doing the above  240 REM A%=&E0:CALL &FFF1 :REM Make the OSWORD call  250 REM PRINT $(X%+4)     :REM Display the returned data  260 :  270 FOR P=0 TO 1  280   P%=load%:O%=mcode%  290   [OPT P*3+4  300   .L2500  310   JMP L2505                   :\ Conventionally, the first two instructions  320   .OldUSERV                   :\ are the entry point and the old USERV.  330   EQUW L2500                  :\ Swapped with USERV to claim.  340   .L2505  350   CMP #myOSW:BEQ L250C        :\ If my OSWORD, jump to respond.  360   JMP (OldUSERV)              :\ Continue via OldUSERV.  370   :  380   \ Our OSWORD routine. The OSWORD handler has already set up the OSWORD  390   \ call, (&F0) points to the control block, IRQs are disabled, A/X/Y do  400   \ not need to be preserved, IRQs are restored on exit.  410   .L250C  420   LDY #2:LDA (ctrl),Y         :\ Get the command in byte 2  430   \  440   \ For this demo, we'll just use the command byte as an index into some  450   \ data to return. NOTE, this demo does not check for out-of-range values.  460   \  470   TAX                         :\ Index into returned data.  480   LDY #4                      :\ Return the data at XY+4 onwards.  490   .LOOP  500   LDA data,X                  :\ Get some data.  510   STA (ctrl),Y                :\ Return the data in the control block.  520   INX:INY                     :\ Step to next byte.  530   CMP #13:BNE LOOP            :\ Copy up to a <cr>.  540   RTS                         :\ All done. Return to OSWORD handler to restore  550   :                           :\ things and return to the caller.  560   .data  570   EQUS "HELLO WORLD":EQUB 13  :\ Our data  580   \  590   \  600   \ To set up the code we need to install it in the I/O processor. The simplest  610   \ way to do this is *RUN it. NOTE, this code does not check if the code already  620   \ exists.  630   .exec%  640   LDY #1                      :\ Prepare to swap pairs of bytes.  650   .SetupLp  660   LDX OldUSERV,Y              :\ Get new vector stored in old vector  670   LDA USERV,Y                 :\ Get current system vector  680   STA OldUSERV,Y              :\ Keep the current vector in the old vector  690   TXA:STA USERV,Y             :\ And set the system vector  700   DEY:BPL SetupLp             :\ Do this for both bytes  710   RTS                         :\ Exit  720   :  730   ]NEXT  740 A$=fname$+" "+STR$~mcode%+" "+STR$~O%+" "+STR$~(exec%OR&FFFF0000)+" "+STR$~load%  750 PRINT"Saving ";A$;:OSCLI "SAVE "+A$:PRINT:END