/*
* Transfer (i.e. exchange) one "word" with selected SPI device.
* Typically one word is 8-bits (an octet), but it does not need to be,
* this function is word-width agnostic - when using the SSC.
* However, for PIO bit-banging, then one word is explicitly
* unconditionally assumed to be exactly 8-bits in length.
*
* input: "out" is word to be send to slave SPI device
* returns: one word read from the slave SPI device
*
* It is the caller's responsibility to ensure that the
* chip select (SPI_NOTCS) is correctly asserted.
*/
static unsigned int spi_xfer_one_word(const unsigned int out)
{
unsigned int in = 0;
#if defined(CONFIG_SOFT_SPI) /* Use PIO Bit-Banging for SPI */
signed int i;
for(i=7; i>=0; i--) /* for each bit in turn ... */
{ /* do 8 bits, msb first */
SPI_SCL(0); /* SPI_CLK = low */
SPI_SDA(out & (1u<<i)); /* output next bit on SPI_DOUT */
SPI_DELAY; /* clock low cycle */
SPI_SCL(1); /* SPI_CLK = high */
SPI_DELAY; /* sample on RISING clock edge */
in <<= 1; /* shift */
in |= SPI_READ; /* get next bit from SPI_DIN */
}
#else /* Use SSC for SPI */
/* write out data 'out' */
ssc_write(SSC_TBUF, out);
/* wait for Receive Buffer Full flag to be asserted */
while ((ssc_read(SSC_STAT) & SSC_STAT_RIR) == 0)
{
; /* busy poll - do nothing */
}
/* read in data */
in = ssc_read(SSC_RBUF);
#endif /* CONFIG_SOFT_SPI */
/* return exchanged data */
return in;
}
static void spi_write(unsigned char b)
{
for(int i = 7; i >= 0; i--)
{
SPI_SCL(false);
spi_delay();
SPI_SDO((b >> i) & 1);
spi_delay();
SPI_SCL(true);
spi_delay();
}
}
void spi_cs_activate(struct spi_slave *slave)
{
gpio_set_value(CONFIG_SOFT_SPI_GPIO_CS,
!(CONFIG_SOFT_SPI_MODE & SPI_CS_HIGH));
SPI_SCL(1);
gpio_set_value(CONFIG_SOFT_SPI_GPIO_CS,
CONFIG_SOFT_SPI_MODE & SPI_CS_HIGH);
}
