Lpc2000

brightside_design wrote:

>I have a problem with a simple SPI example program.
>Part: LPC2129
>PCK: 14.7 MHz
>Mode: Master, CPOL=0, CPHA=0, LSIF=0.
>
>I initialise the SPI like this:-
>void SPI_Init(void)
>   {
>	S0SPCCR = 0x26;	// Divides PCK to give about 400kHz
>	S0SPCR = 0x20;	// Select Master mode
>   }
>
>And then use the SPI like this:-
>void SPI_Transfer( char *buf, int count)
>{
>	int r = 0, i = 0;
>
>	for( ; i < count; i++ )
>	{
>		S0SPDR = buf[i];	// Write data
>		do{ r = S0SPSR; }while(!(r & 0x80));// Wait for SPIF
>		// Read status - to be done
>		buf[i] = S0SPDR;	// Read data
>	}
>}
>
>  
>

Try writing it this way:

void SPI_Transfer( char *buf, int count)
{
volatile int r = 0;
volatile int i = 0;
	for( ; i < count; i++ )
	{
		S0SPDR = buf[i];	// Write data
		do{ r = S0SPSR; }while(!(r & 0x80));// Wait for SPIF
		// Read status - to be done
		buf[i] = S0SPDR;	// Read data
	}
}


If you look deeper at the underlying assembly language via the JTAG, I'm 
fairly confident you will find that it reads "r" once, then loops on the 
resultant value.  Essentially, the volatile keyword tells the compiler 
to assume nothing about the variables' value it holds, to actually check 
it rather than to optimize the reference.

YMMV, but your function would probably work if you turned off all 
optimizations (-O0).

TomW


>Sometimes I power up the device and this function runs correctly 
>with problem whatsoever. Other times the function just hangs. If I 
>attach a JTAG debugger (Keil ULINK) I find that the function is 
>hanging at the line "do{ r = S0SPSR; }while(!(r & 0x80));" on the 
>first itteration.
>
>There is no hardware attached to the SPI port. I figured that the 
>device should put data out onto an unconnected pin without any 
>problem and that I should be able to get the software working before 
>thinking about ading hardware.
>
>Has anyone got any ideas what might be going wrong?
>
>Thanks,
>
>Paul
>
>
>
>
>
> 
>Yahoo! Groups Links
>
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>
> 
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>  
>


-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
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