Lpc2000

--- In lpc2000@yahoogroups.com, Tom Walsh <tom@...> wrote:
>
> 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
> 
> 
> -- 
> Tom Walsh - WN3L - Embedded Systems Consultant
> http://openhardware.net, http://cyberiansoftware.com
> "Windows? No thanks, I have work to do..."
> ----------------------------------------------------
>

Thanks Tom, I will try that when I have a moment but I don't think 
thats the answer. I've just read through the disassemby for that 
function and it is reading the register each time through. Also the 
problem is intermittant, sometimes it works fine, other times it 
hangs.

Paul