Problems with NIOS II SPI communication

Hi,

I'm using two DE0 board to communicate with SPI core. One configued as master and another as slave.

I tried to check spi status register to complement the slave code. And whole process is the master send data-- 0xabcd,and the slave receive the data and send back. But I found that the master can't receive the right data sometimes, less than 50% time the received data is right.

I run the master program with debug mode first and then run the slave one to avoid signal toggle on the slave's input side. I set SCLK from 128kHz to 1MHz,the problem is still there.

Here is my code for slave:

int main(void)

{

alt_u32 rddata=0x0;

alt_u32 status;

IOWR_ALTERA_AVALON_SPI_STATUS(SPI_BASE,0x0000);

IOWR_ALTERA_AVALON_SPI_TXDATA(SPI_BASE,0x1001);

IORD_ALTERA_AVALON_SPI_RXDATA(SPI_BASE);

while(1)

{

do

{

status = IORD_ALTERA_AVALON_SPI_STATUS(SPI_BASE);

}

while((status & ALTERA_AVALON_SPI_STATUS_RRDY_MSK)==0 &&

(status & ALTERA_AVALON_SPI_STATUS_RRDY_MSK) == 0);

rddata= IORD_ALTERA_AVALON_SPI_RXDATA(SPI_BASE);

IOWR_ALTERA_AVALON_SPI_TXDATA(SPI_BASE, rddata);

}

Code for master is :

int main(void)

{

void send(alt_u16 write);

alt_u16 receive();

alt_u16 wrdata=0xabcd;

alt_u16 rddata;

IOWR_ALTERA_AVALON_SPI_SLAVE_SEL(SPI_BASE, 1);

IORD_ALTERA_AVALON_SPI_RXDATA(SPI_BASE);

while(1)

{

send(wrdata);

rddata=receive();

}

return 0;

}

void send(alt_u16 write)

{

alt_u32 status;

alt_u16 data;

IOWR_ALTERA_AVALON_SPI_CONTROL(SPI_BASE, 0x0400);

IORD_ALTERA_AVALON_SPI_RXDATA(SPI_BASE);

do

{

status = IORD_ALTERA_AVALON_SPI_STATUS(SPI_BASE);

}

while (((status & ALTERA_AVALON_SPI_STATUS_TRDY_MSK) == 0)&&

(status & ALTERA_AVALON_SPI_STATUS_RRDY_MSK) == 0);

IOWR_ALTERA_AVALON_SPI_TXDATA(SPI_BASE , write);

data=IORD_ALTERA_AVALON_SPI_RXDATA(SPI_BASE);

do

{

status = IORD_ALTERA_AVALON_SPI_STATUS(SPI_BASE);

}

while ((status & ALTERA_AVALON_SPI_STATUS_TMT_MSK) == 0);

IOWR_ALTERA_AVALON_SPI_CONTROL(SPI_BASE, 0);

}

alt_u16 receive()

{

alt_u16 data;

alt_u32 status;

IOWR_ALTERA_AVALON_SPI_CONTROL(SPI_BASE, 0x0400);

IORD_ALTERA_AVALON_SPI_RXDATA(SPI_BASE);

do

{

status = IORD_ALTERA_AVALON_SPI_STATUS(SPI_BASE);

}

while (((status & ALTERA_AVALON_SPI_STATUS_TRDY_MSK) == 0 ) &&

(status & ALTERA_AVALON_SPI_STATUS_RRDY_MSK) == 0);

IOWR_ALTERA_AVALON_SPI_TXDATA(SPI_BASE , 0x00);

data=IORD_ALTERA_AVALON_SPI_RXDATA(SPI_BASE);

do

{

status = IORD_ALTERA_AVALON_SPI_STATUS(SPI_BASE);

}

while ((status & ALTERA_AVALON_SPI_STATUS_TMT_MSK) == 0);

IOWR_ALTERA_AVALON_SPI_CONTROL(SPI_BASE, 0);

return data;

}

Can anybody help on this problem? I think there maybe some mistake in my code. Has anybody use SPI core as a slave? Most people use the SPI core as a master, I really need some on the slave mode. Thank a lot!