spi.c

Interfacing to an MMC/SD card via SPI (for microcontroller)

#include <ecog.h>
#include <ecog1.h>
#include "mmcConf.h"   // Include the SPI CS defines


/******************************************************************************
NAME
    spiTransferByte

SYNOPSIS
    static unsigned int spiTransferByte(unsigned int mosi)

FUNCTIONS
    Simultaneously transmits and receives one byte on the SPI.

RETURNS
   The MISO signal that was received.
******************************************************************************/

unsigned int spiTransferByte(unsigned int mosi)
{
    static unsigned int miso = 0;
    
    // Should not write/read to the _last registers in the tx/rx registers        
    // Transmit the byte
    rg.dusart.a0_tx8 = mosi;
    
    /* Wait for the transaction.
     * The usart tx_?_ready signals arrive when the output data is transferred
	 * from the tx register to the output shift register. This is before the
	 * data transfer has completed, so we must wait for the rx_?_rdy status
     * which only occurs when all receive data bits have arrived
     */
	while (fd.dusart.a_int_sts.tx0_rdy != 1)
		;
	while (fd.dusart.a_int_sts.rx0_1b_rdy != 1)
		;
    
    // Read the received data byte
    miso = rg.dusart.a0_rx8;
    
    return (miso);
}



/******************************************************************************
NAME
    spiAssertCS

SYNOPSIS
    static void spiAssertCS(void)

FUNCTION
    Asserts the SPI chip select signal CS0 for internal use
    and GPIO16 for the external device chip select.

RETURNS
    Nothing.
******************************************************************************/

void spiAssertCS(void)
{
    /* The MMC/SD card daughter board uses GPIO22 for CS.
     * The hardware does not allow the CS signal to stay asserted
     * for more than one single SPI transfer, so this is done manually.
     * Chip select 0 must be asserted internally to enable data to be received.
     * There are two problems in the hardware:
     *   1. CS0 must be asserted to enable data reception.
     *   2. CS does not stay asserted across byte boundaries.
     */
	
 	// Enable transmit and receive
    rg.dusart.spi_ctrl = DUSART_SPI_CTRL_RX_EN_MASK | DUSART_SPI_CTRL_TX_EN_MASK;
    MMC_CS_Set = 1;
    fd.dusart.spi_frame_ctrl.tx_slave_sel = 1;	// Assert CS0 internally
	LED2_Set = 1;      // Turn on the LED to indicate accessing
}



/******************************************************************************
NAME
    spiDeassertCS

SYNOPSIS
    static void spiDeassertCS(void)

FUNCTION
    Deasserts all chip selects.

RETURNS
    Nothing.
******************************************************************************/

void spiDeassertCS(void)
{
    // See comments for spiAssertCS()
    MMC_CS_Clr = 1;
    fd.dusart.spi_frame_ctrl.tx_slave_sel = 0;
	// Disable transmit and receive
    rg.dusart.spi_ctrl = DUSART_SPI_CTRL_RX_DIS_MASK | DUSART_SPI_CTRL_TX_DIS_MASK;
    LED2_Clr = 1;      // Turn off indicator LED
}