18F452 Interrupt Probelm

c_bellsham · Joined: 27 Oct 2005 Posts: 7

Hi,
We are using CCS PCWH 3.212 for a PIC 18F452 project.

We think we've found a problem (that you may already be aware of) with the Low Priority interrupt.
It appears that the code generated for the inetrrupt vector 00018h doesn't save the STATUS register after saving the W register.
the code at vector 00008h does save the STATUS.
Is this a known problem?
Is there an update?
Or is there a snippet of code that someone could recomend

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

c_bellsham · Joined: 27 Oct 2005 Posts: 7

0008: MOVWF 05------------Saving W
000A: MOVFF FD8,06-------Saving Status
000E: MOVF FE9,W
0010: MOVWF 07
0012: MOVF FEA,W
0014: MOVWF 08
0016: MOVF FE1,W
0018: MOVWF 09-----------Saving W
001A: MOVF FE2,W--------Saving FSR using MOVF which affects Status!!!!!
001C: MOVWF 0A
001E: MOVF FD9,W
0020: MOVWF 0B

Ttelmah · Guest

Remember, that if the fast interrupt feature is not used, it is the low priority interrupt that sits at address 8. The code being shown, is the standard code for a system _only_ using low priority interrupts. Nothing will ever jump into this at address 18H.
If you enable hardware priority interrupts, then the code shown will be at address 18H, and at address 8, there will be a jump, to go 'round' this handler. This is one really annoying thing about the hardware design (it should be the low priority handler that stays at address 8).
I suspect you may be confusing the 'priority' command (which is only a command to alter the order in which the interrupt handlers are parsed in the code, ad pre-dates the introduction of hardware 'priorities'). The high priority interrupts require the 'high' command, and you can also use the 'FAST' command to allow the RETFIE 1 instruction (which automatically restores these registers).
the handler loaded with 'HIGH' used, is:

prwatCCS · Joined: 10 Dec 2003 Posts: 70 Location: West Sussex, UK

I have sucessfully used v3.212 to generate code for the 18F252, 18F452 and 18F6621 using both High and Low (hardware) priority interrupts.

I have serial data at 250KB (fx and Rx irq) , timer0 and A2D conversion low prority interrupts and a Timer2 fast irq running.

Others have noted about the location of your irq vectors based on whether or not you are using both priorities, so I dont think you have correctly identified a problem. However, I would draw your attention to a problem I found with the use of the FAST irq code generation, whereby the compiler may incorrectly assume that Bank0 is mapped in on entry to the fast irq hander.

Please see my post titled 18fxx2/ compiler v2.236 FAST IRQ problem.

regards
_________________
Peter Willis
Development Director
Howard Eaton Lighting Ltd UK

c_bellsham · Joined: 27 Oct 2005 Posts: 7

Firstly, Many thanks for your help, I appreciate it!

We are trying to use both high and low priority interrupts.

Is there a way of telling the compiler that we are trying to use priority interrupts.
Currently we're only configuring the registers to do priority inetrrupts.
Does the compiler check what we are doing with these bits and then decide or is there a check box that we should be ticking?

rnielsen · Joined: 23 Sep 2003 Posts: 852 Location: Utah

I'm not sure if this has anything to do with what you're seeing but there was a bug fix for interrupts after v3.212.

Guest · Posted: Thu Oct 27, 2005 8:35 am

My approach is to place the #priority in my header file.

NOTE : this only sets the order in which the low (hardware) priority irqs are serviced, and has nothing to do with the FAST irq (aka high hardware priority)

Ttelmah · Guest

The _priority_ command, has nothing to do with using the high priority interrupt ability. All this does, is set the order in which the interrupts are scanned, inside the single global interrupt handler. It predates the introduction of high priority hardware interrupts.
The command for using high priority _hardware_ interrupts, is the 'HIGH' instruction, added after the interrupt declaration. So:

c_bellsham · Joined: 27 Oct 2005 Posts: 7

This is really starting to get on my wick.

I've added the line:-
#device PIC18F452 ICD=TRUE HIGH_INTS=TRUE
and I get the following error:-
Error 104 Extra Characters on the preprocessor command line.

So I removed that and tried the FAST:-
#int_LOWVOLT FAST
void LOWVOLT_isr(void)
And I get an error:-
Error 159 Invalid interrupt direcive Requires #device HIGH_INTS=TRUE
So I add that line back in and then I get both error 104 and 159

what the hell is going on with this dumb thing?
Or is it me?

Guest · Posted: Thu Nov 17, 2005 8:24 am

Why not just put what it asks for, instead of trying to be 'smart', and put the commands onto one line?.
#include <18F452.h>
#device HIGH_INTS=true

Works fine for me.

Best Wishes

dyeatman · Joined: 06 Sep 2003 Posts: 1934 Location: Norman, OK

For what it's worth I see the same problem with version 3.236, but this compiles with no problems:

#include <18F452.h>
#device ICD=TRUE
#device HIGH_INTS=TRUE

P.S. Guest (TTelmah?), it seems you just beat me!!!

Ttelmah · Guest

It is amazing how often that happens... :-)
The compiler currently, is a bit 'undocumented' in this regard. It is 'odd' that commands like the ADC one, can be put on once line, or left seperate, but these new ones, seem to require the seperate lines.

Best Wishes