SPI fail

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IsThisNameTaken...
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Posted by IsThisNameTaken...: Wed. Mar 24, 2010 - 07:05 PM
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I have a real simple SPI function that reads by sending a dummy byte. I also have the uart up and running for debug work. This function comes from the Fatfs demo for anyone who wonders.

Anyway, the init function calls rcvr_spi 10 times to wake up the card or something, but it always hangs. I added the uart output to see what was happening and the best case so far is 5 transmissions with an average of 2-3 before freezing.

Why would the SPIF bit fail to set? I have no SPI interrupts enabled (I'm in master mode).


#define DD_MOSI   2
#define DD_SCK   1
#define DDR_SPI   DDRB
#define DD_SS   4

.....SPI init code


	DDR_SPI = (1<<DD_MOSI)|(1<<DD_SCK)| (1<<DD_SS);
	SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR1); /* Initialize SPI port (Mode 0) */

.....


//SPI receive via dummy send
static
BYTE rcvr_spi (void)
{
	SPDR = 0xFF;
	xputs(PSTR("SPI get\n"));
	loop_until_bit_is_set(SPSR, SPIF);
	return SPDR;
}

EDIT: also tried to go with a while loop in place of the loop_until_bit_is_set() macro thingy, no dice.

Tags:

Tools, Compilers and General Programming
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Bronze Markdavid.prentice
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Posted by david.prentice: Wed. Mar 24, 2010 - 07:37 PM
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I can never understand why people have to complicate SPI. You only need a single function. You always have an in and an out. You just 'out' a dummy if you only want the 'in'.

unsigned char spi(unsigned char data)
{
    SPDR = data;
    while ((SPSR & (1<<SPIF)) == 0) ;
    return SPDR;
}

The FatFS code should work straight out of the box. Remember to implement the Card-Detect and Write-protect.

And of course wire the lines correctly.

David.

p.s. I am well aware that ARM SPI can do some very clever things. The AVR can't. So why not keep it simple?

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IsThisNameTaken...
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Posted by IsThisNameTaken...: Wed. Mar 24, 2010 - 08:01 PM
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david.prentice wrote:

The FatFS code should work straight out of the box. Remember to implement the Card-Detect and Write-protect.

... Yeah it SHOULD work straight out of the box but it doesn't and that's why I am posting. The SPI function freezes after a few uses. I am running the demo on a mega64 and have all the connections done up properly.

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Bronze Markdavid.prentice
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Posted by david.prentice: Wed. Mar 24, 2010 - 08:24 PM
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Well, the code is written for a mega64. It DOES work out of the box.

Re-install the ZIP file and start again.

David.

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Torby
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Posted by Torby: Thu. Mar 25, 2010 - 04:03 PM
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hahah... I can kill ANYTHING that makes sense in 2 lines of code or less!

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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Bronze Marktheusch
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Posted by theusch: Thu. Mar 25, 2010 - 05:03 PM
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Quote:

I can never understand why people have to complicate SPI. You only need a single function.

In fairness to the OP, the fatfs stuff has the twin routines built. (And they work OK for me.)

Note that these are used along with a timeout. Have you set up the timing functions?

It is strange, as the wakeup is 80 dummy clocks. And master SPI should work fine.

You don't have a floating /SS by any chance?

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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