Part 2 :- SWIs and data-shifting BY DF0: / NFA Having got the basics of setting up a machine code program,I will now detail some data-shifting commands.Note that this is all for the Archimedes computer! See <> Issue for the preface to this! ----------------------------------------------------------------------- Basic movment command :- LDR , This can be moved for transfer between registers and memory locations. Address command : ADR , . This loads the destination ( often a register with the address of a label,IE:- ADR R0,poopoo Would give R0 the value of wherever .poopoo is in memory. See last issues file for more on this and branches. Mathmatical operations:- ------------------------- ADD : Addition : ADD {Suffix} ,, ADC : Add with carry : ADC {Suffix} ,, SUB : Subtract : SUB {Suffix} ,, SBC : Sub with carry : SBC {Suffix} ,, RSB : Reverse Sub : RSB {Suffix} ,, RSC : RSB with carry : RSC {Suffix} ,, MOV : Move data 2 reg: MOV {Suffix} , MVN : MOV inverted : MVN {Suffix} , CMP : Compare : CMP {Suffix} , AND : Logical AND : AND {Suffix} ,, ORR : Logical OR : ORR {Suffix} ,, EOR : Logical EOR : EOR {Suffix} ,, BIC : Bit clear : BIC {Suffix} ,, TST : Test bits : TST {Suffix} , MUL : Multiply : MUL {Suffix} ,, Where {Suffix} is is one of the following :- EQ : Equal to NE : Not equal VS : Overfolow set VC : Overfolw clear PL : Plus MI : Minus CS : Carry set CC : Carry clear AL : Always NV : Never HI : Higher - Unsigned - LS : Lower than or same - Unsigned - LT : Less than - Signed - GT : Greater than - Signed - LE : Lessthan or equal - Signed - Example code : ---------------- .Start CMP R0,R1 ; Compare registers R0 and R1. MOVEQ PC,R14 ; If they are EQual,then end program ADDNE R0,R0,#1 ; If Not EQual,add a value of 1 to R0 B .Start ; Branch back to beginning to start again. I have introduced you to a new command there,the B command.This will jump to any label specified after it.If you use a BL,this acts as a Branched sub-routine.Example :- +----- BL .Subthing ; Branch to .Subthing label. | <-+ ; Now back from sub-routine. | .. | | .. +------------------------------------------------------+ | .. | | | +-----> .Subthing | | ; A completley pointless sub-routine | | MOV R15,R14 ; Equivalent of RTS return call --------+ New topic Thingy - Software Interrupts =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Software interrupts,when called cause the computer to halt the current program,switch to supervisor mode,and to execute the named SWI. Examples are the write text SWI, "OS_WriteC",which prints out the character in register R0.I am now going to cover some common SWIs.They are all called with the SWI command,like so: SWI "OS_WriteC" Note that the SWI has to be in "" marks,and will not work unless the case is exactly correct. SWI "OS_writec" is wrong.You can also use the numerical value,so SWI "OS_WriteC" and SWI &00 both do the same thing. SWIs: ----- Note that all text strings must be terminated in a zero,unless they are CLI strings,in which case they must end in a &0D. OS_WriteC : Writes an ASCII character Numerical value : &00 Entry : R0 holds ASCII value Exit : No information returned OS_ReadC : Reads a key from the keyboard Numerical value : &04 Entry : Nothing passed Exit : R0 holds ASCII value of key OS_Write0 : Prints a string of text Numerical value : &02 Entry : R0 holds address of string loaded with ADR Exit : No information returned OS_WriteS : Prints a string Numerical value : &01 Entry : Nothing passed Exit : Nothing passed --[ This may sound a bit wierd,but it works like this : EQUS ("This is a string printed with OS_WriteS...") EQUB &0 SWI "OS_WriteS" ]-- OS_ReadLine : Reads a line of text Numerical value : &0E Entry : R0 = Address of buffer to hold string R1 = Maximum length for string R2 = Lowest ASCII code allowed in buffer R3 = Highest ASCII code allowed in buffer Exit : R1 = Length of buffer OS_NewLine : Outputs an enter character Numerical value : &03 Entry : Nothing passed Exit : Nothing passed OS_CLI : Executes a CLI string. Numerical value : &05 Entry : R0 = Address of command string Exit : Depends on command being run... Example of OS_CLI :- ADR R0,CommandString ; Load address of label into R0 SWI "OS_CLI" ; Call SWI MOV PC,R14 ; End program .CommandString ; Label of string EQUS "*DIR" ; Actual string EQUB &0D ; Terminated in &0D An example program that covers the topics I have written down here would be :- ; Reads keypresses and loops around until a 'Z' is pressed ; Example program by DF0: of NFA in 1994 .Start ; Identify programs start label LDR R3,#0 ; Load R3 with 0 LDR R1,#ASC("Z") ; Load R1 with ASCII value of 'Z' SWI "OS_ReadC" ; Read a character from the Keyboard BL Checkchar ; Branch to sub routine CMP R3,#1 ; Compare R3 with 1 value BNE Start ; If not 1 hen loop back to Start MOVEQ PC,R14 ; If equal then exit program .Checkchar ; CheckChar sub-routine CMP R0,R1 ; Compare key press with 'Z' LDREQ R3,#1 ; If the same then load R3 with 1 MOV R15,R14 ; Return from sub-routine Well,thats about it for now! Until next time..... BYE! From DF0: / NFA **PLUG**PLUG**PLUG**PLUG**PLUG**PLUG**PLUG**PLUG**PLUG**PLUG**PLUG**PL Hey,folks! An important message for all you Archimedes owners! Coming soon to an ADFS disk near you is the miraculous program, -> NFADesk <- Liven up your Desktop! Have lots of cool 3-D icons! Have music in the background! Load 24-bit images as backdrops ( If you have a RISC PC ) ! Generally cock about! Give money to me! Yes,you heard that right! I am releasing a PD program that jazzes up your boooring Desktop no end! At the moment, features to be included are :---- -*- New Icons for windows and ROMApps -*- New system modules for extended commands -*- Backdrop loader for RISC-OS 3 and greater -*- System$Paths set up for all major applications -*- Virus protection -*- Choice of pre-made configurations -*- Module utility to unplug all modules you dont want! -*- ARM BASIC editor -*- Support for Amiga Soundtracker and MusMod files -*- And a damn sight more ! It'll probably be finished early 1995,as I have far more important things to do in the interim,namely study like hell..... When it does come though,itll be a bit damn kicking!! *****************************END OF PLUG****************************** End. (honest)