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Re: [avr-gcc-list] direct port access

From: E. Weddington
Subject: Re: [avr-gcc-list] direct port access
Date: Wed, 22 Jan 2003 14:58:38 -0700

On 22 Jan 2003 at 10:57, Marlin Unruh wrote:

> I have some code that was working with the old style io.h. I am tring
> to get the code working with the new style (#define
> PORTD _SFR_IO8(0x12))
> void Pdu1_In_Port(unsigned char* buff)
> {
>  unsigned char tmp;
>  unsigned char * const iobase = (unsigned char*)0x20;
>  unsigned char address;
>  address = buff[10]; // get address of port
>  if(address < SPL) { // exclude SREG and Stack Pointer Registers
>   tmp = *(iobase + address); // read i/o space address
>   tmp &= ~buff[6]; // inverted mask low byte AND
>   tmp |= (buff[6] & buff[8]); // get data low byte
>   *(iobase + address) = tmp; // write i/o space
>  }
> } // end of Pdu1_In_Port

Well you didn't say what the above code is actually doing in it's 

But this could be a problem:

if(address < SPL) { // exclude SREG and Stack Pointer Registers

SPL is defined as a _SFR_IO8(..., which is not going to be the same 
thing as what your address is declared as. Rewrite as:

if(address < &(SPL))

That way you're comparing a memory address to a memory address.

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