Beefy Boxes and Bandwidth Generously Provided by pair Networks
There's more than one way to do things
 
PerlMonks  

comment on

( [id://3333]=superdoc: print w/replies, xml ) Need Help??
Both run on 6502 processors.

Code #1 is a delay loop.
Code #2 is a 16 bit unsigned multiply (multiplies $20/$21 by $22/$23, returning the result in $24/$25/$26/$27).

Update: OK, I couldn't resist. I dug out the 6502 assembler and emulator to test code #2. Now, admittedly, the emulator could be broken, but I didn't get any results that made sense for either a multiply or divide. I spent about 45 minutes playing with this, and the simulator seems to be executing as I would expect. But the resulting $26/$27 locations never come up with any valid values using $20/$21 and $22/$23 as inputs (the higher address is the high byte of each word, so I had byte ordering correct).

And since code #1 was going for maximum delay, you could have gotten a little more delay by changing it to:
start	LDY #$FF    
loop1	LDX #$FF  
loop2	DEX       
	BNE loop2  
	DEY        
	BNE loop2  
	RTS           
You're resetting X to #$FF, when it's already 0, losing 255 free 2 cycle delays.

--Chris

e-mail jcwren

In reply to (jcwren) RE: (2) What was your first program? by jcwren
in thread What was your first program? by Ovid

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or How to display code and escape characters are good places to start.
Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?
Chatterbox?
and the web crawler heard nothing...

How do I use this?Last hourOther CB clients
Other Users?
Others scrutinizing the Monastery: (4)
As of 2024-03-28 15:24 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    No recent polls found