 |
 |
| View previous topic :: View next topic |
| Author |
Message |
ECL
Guest
|
| PCH indirect addressing generated code |
 Posted: Mon Jun 28, 2004 6:26 pm |
 |
|
I'm new to PIC asm, and I'm learning by looking at compiler output. I'd like to optimize an isr to be as few instructions as possible. Most of my code is in C, but the isr is in assembly.
This code for a pointer stored in the access RAM to data elsewhere:
generates
| Code: | MOVF 56,W
MOVWF FSR0L
MOVFF 57,FSR0H
MOVFF INDF0,70A
MOVFF 70A,LATD |
This is with PCH version 3.202 with a 18F6720 target MCU. Note that the BSR is not needed (yea!). Does anyone know:
1) Why the move to 70A, then 70A to LATD. Can it just be LATD?
2) Can I map my pointer to FSRx and just use that directly, or at least reserve one FSRx for my own asm routines to use? I can avoid a lot of moves that way and save cycles (any maybe use post increments too).
Thanks in advance to all you asm mavens for your help![/code] |
|
 |
Neutone
Joined: 08 Sep 2003
Posts: 839
Location: Houston
|
|
| Posted: Tue Jun 29, 2004 7:42 am |
|
|
| There are three FSR's I have never compiled code that I noticed was using the thrid. Your probably safe using the third with interupts but don't take my word for it because things have a way of changing. Post increments should work if you only need a single interupt with indirect addressing. |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
FAQ 
Search
Register
Profile 
Log in to check your private messages 
Log in
