topic Re: Hi, I'm converting over from using the IAR compiler for... in CodeWarrior for MCU

Hi, I'm converting over from using the IAR compiler for...

electropw — Tue, 18 Mar 2008 10:40:43 GMT

Hi,

I'm converting over from using the IAR compiler for the HCS12.

I have found that CodeWarrior does not support a nifty function generation attribute called "__monitor".

This attribute causes the function to generate code to, on entry, save the current interrupt enable status & disable interrupts; then, on exit, restore the saved interrupt enable status.

This is a really useful tool.

Does anyone know of an implementation work around for CodeWarrior or whether Freescale intends to support this functionality?

regards

PhilW

Re: Hi, I'm converting over from using the IAR compiler for...

Lundin — Tue, 18 Mar 2008 14:30:13 GMT

If you mean the global interrupt enable/disable (the "I" bit in the condition code register), this is done by the hardware.

If you mean the cause of the interrupt, there is no support for it as far as I know. There is no big deal looking it up yourself, since you need to know how every interrupt work anyway. They all tend to be somewhat different, and so is the way to clear the interrupt flags.

Re: Hi, I'm converting over from using the IAR compiler for...

bigmac — Tue, 18 Mar 2008 16:59:38 GMT

Hello Phil,

I am not sure whether this provides what you require -

void func( void)

{

__asm pshc; // Save current CCR state

__asm sei; // Disable interrupts

/* Function code here */

__asm pulc; // Restore previous CCR state

}

Regards,

Mac

Re: Hi, I'm converting over from using the IAR compiler for...

electropw — Thu, 20 Mar 2008 08:11:42 GMT

Hi Mac,

Thanks for your reply. Yes I tried this, created a coupla macros to do it.

Unfortunately it is not versatile enough unless you have a simple function that falls straight through or you write your code specifically to support the macro insertions.

For example you may try

char function ( a,b )

{

SaveIEstatusDisableI;

return a + b;

RestoreIEStatus;

}

This will not work since the compiler automatically generates the return code in the return statement and then inserts the macro code following it, and it will never be executed.

The beauty of the IAR __monitor keyword is that it does the IE status saving and resoration automatically, no matter how many return statements you may have within your function.

regards

Phil

Re: Hi, I'm converting over from using the IAR compiler for...

bigmac — Thu, 20 Mar 2008 09:50:15 GMT

Hello Phil,

In this case, you would need to place the restore macro just prior to each return statement. Or perhaps create another macro that provides both the restore and return process.

#define _critical __asm pshc; __asm sei;

#define _critical_return(x) __asm pulc; return(x);

Obviously not quite as convenient as having a special compiler specific keyword available.

Regards,

Mac

Re: Hi, I'm converting over from using the IAR compiler for...

electropw — Thu, 20 Mar 2008 10:57:48 GMT

Hi Mac,

Good idea.

I'll try it.

Thanks again.

Re: Hi, I'm converting over from using the IAR compiler for...

electropw — Thu, 20 Mar 2008 11:27:11 GMT

Hi Mac,

Bugger!!!!

will not work either, very close though.

Will depend in what you are doing in the code as to how you would implement the use.

To explain, One of the uses I had in mind was to protect a global variables value whilst reading it or writing it, either in an IRQ or in a background access.

int read_x( int x )

{

return x;

}

This produces code, LDD x; RTS.

With our solution

int read_x( int x )

{

_critical

_critical_return (x)

}

produces

PSHC

SEI

PULC

LDD x

RTS

A pointless operation huh!

We would have to try and maybe load a local with x and return the local and then ensure the compiler

does not optimize out our uae of the local.

I have contacted CodeWarrior and they tell me they will look at it and put it on the requested functionality

list. So no immediate nice solution, if there ever will be.

I might try and see if I can do some sort of macro function call and embedd our solution in there, maybe!!

regards

Phil

Re: Hi, I'm converting over from using the IAR compiler for...

bigmac — Thu, 20 Mar 2008 12:18:10 GMT

Hello Phil,

The LDD x instruction would represent the compiler output corresponding with the return(x); statement, for a 16-bit return value. So the assembly code is what might be expected.

Passing the current value of a global variable to the function, via the parameter x will simply result in the return of that value, independent of what a subsequent interrupt may do to the contents of the global variable.

If you needed to prevent the occurrence of an interrupt altering a global variable whilst a function manipulates its value, and then to return the newly modified value, the following approach might work -

int g_var1;

int func( int y)

{

_critical;

g_var1 += y;

y = g_var1;

_critical_return(y);

}

You could not use the statement _critical_return(g_var1); since an interrupt might possibly occur between the PULC and the LDD instructions.

Regards,

Mac

Message Edited by bigmac on 2008-03-20 04:22 PM

Re: Hi, I'm converting over from using the IAR compiler for...

electropw — Thu, 20 Mar 2008 12:38:59 GMT

Hi Mac,

Exactly what I was trying to say above.

I also know that the IAR compiler is, I imagine also CW to be also, smart enough to optimise out the y=g_var1; statement and just return g_var1. This effectively nulifies what we were trying to do.

Please note that my sample was simply that, a sample. Just shown to simply describe the compiler operation. I know in real life with the HC12 that there is no need to protect int sized variables in such operations since it is a single instruction operation and therefore cannot be corrupted by an interrupt occuring during the access. The ones of concern are the variables > 2 bytes in size.

regards

Phil

Re: Hi, I'm converting over from using the IAR compiler for...

bigmac — Thu, 20 Mar 2008 13:47:52 GMT

Hello Phil,

It might be sufficient to declare the global variable as -

volatile int g_var1;

to prevent that sort of optimisation by the compiler. I guess all global variables that are referenced within ISRs should normally be declared as volatile.

Regards,

Mac

Re: Hi, I'm converting over from using the IAR compiler for...

bigmac — Thu, 20 Mar 2008 15:43:44 GMT

Hello again Phil,

I adapted the macros for HC08 MCU (which I am more familiar with) and then tested the following function to return the value of a long variable -

long g_var1 = 10000L;

long getlong( volatile long *ptr)
{
long temp;

   _critical;
   temp = *ptr;
   _critical_return(temp);
}

long b;

b = getlong( &g_var1);

There didn't appear to be optimisation by the compiler in the manner that you suggested. I also tried a similar function to return a short value, which is also critical for an 8-bit device, with similar results.

Regards,

Mac

Message Edited by bigmac on 2008-03-20 07:46 PM