NIOS II SPI communication

[Altera_Forum]

Hi All! 

I've a problem with Nios SPI communication. I studied "Embedded Peripherals IP User Guide" but I didn't understand how to use alt_avalon_spi_command() function. I understood that an Avalon-MM master peripheral controls and communicates with the SPI core via six 32-bitregisters. So I searched more examples on web but I only found this:   //------------------------------------ MAIN ------------------------------------------------------------  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; }     //-------------------------------------- SEND -------------------------------------------------------------------------     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); }     //----------------------------------- RECEIVE --------------------------------------------------------------------------     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; }  The question is "What's the difference between alt_avalon_spi_command() and IOWR_ALTERA_AVALON_SPI_TXDATA() to transmit a data via SPI"?  Thank you all :)

[Altera_Forum]

The difference should be clear from the description in the user guide? alt_avalon_spi_command() performs the sequence of actions described in the manual, while IOWR_ALTERA_AVALON_SPI_TXDATA() just writes the TXDATA register.  

 You can read the source to the alt_avalon_spi_command() function and see how it uses IOWR_ALTERA_AVALON_SPI_TXDATA() and everything else that it does to gain better understanding.  There is also an example use of the function here: http://www.alterawiki.com/wiki/spi_core

[Altera_Forum]

Thank you, you were so clear. I have another question please. What have I do to set NIOS in slave mode in SPI communication? I explane my problem. I have to load Cyclone V firmware into an external EPCQ128 with a microcontroller that communicates with NIOS via SPI. And so, I need to set my microcontroller as master, and NIOS as slave in SPI communication.

[Altera_Forum]

I tried to write a simple code section in C language to make SPI communication, with NIOS as slave. Can you check if my code is good please? 

 static void spi_rx_isr(void* isr_context);  static void spi_rx_isr(void* isr_context){  IOWR_ALTERA_AVALON_SPI_STATUS(SPI_SLAVE_BASE, 0x0); }  int ret; int status; alt_u16 rddata;  //this registers slave IRQ with NIOS ret = alt_iic_isr_register(SPI_SLAVE_IRQ_INTERRUPT_CONTROLLER_ID,SPI_SLAVE_IRQ,spi_rx_isr,(void *)spi_command_string_tx,0x0);  //check if slave status is good do{  status = IORD_ALTERA_AVALON_SPI_STATUS(SPI_SLAVE_BASE); } while ((status & ALTERA_AVALON_SPI_STATUS_RRDY_MSK) == 0);   //copy received byte into rddata variable rddata = IORD_ALTERA_AVALON_SPI_RXDATA(SPI_SLAVE_BASE);  //set slave IRQ to enable a new byte receiving IOWR_ALTERA_AVALON_SPI_CONTROL(SPI_SLAVE_BASE, ALTERA_AVALON_SPI_CONTROL_SSO_MSK | ALTERA_AVALON_SPI_CONTROL_IRRDY_MSK);

[Altera_Forum]

HI fmv, 

i'm facing the same problems that you had. I tried both codes you have proposed but i still have several problems to obtain data and retransmitt data back to the Master defined as a microcontroller. I was wondering if you could provide me the entire code that you've used in order to solve the problem or some advices to adopt.  Thanks