SOFT_SPI.cpp

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#include "Cosa/Soft/SPI.hh"

using namespace Soft;

SPI::Driver::Driver(Board::DigitalPin cs,
                    Pulse pulse,
                    Clock clock,
                    uint8_t mode,
                    Order order,
                    Interrupt::Handler* irq) :
  m_irq(irq),
  m_cs(cs, (pulse == 0)),
  m_pulse(pulse),
  m_mode(mode),
  m_order(order)
{
  UNUSED(clock);
  m_next = spi.m_list;
  spi.m_list = this;
}

void
SPI::acquire(Driver* dev)
{
  // Acquire the device driver. Wait if busy. Synchronized update
  uint8_t key = lock();
  while (UNLIKELY(m_busy)) {
    unlock(key);
    yield();
    key = lock();
  }
  // Set current device and mark as busy
  m_busy = true;
  m_dev = dev;
  // Set clock polarity
  m_sck.write(dev->m_mode & 0x02);
  // Disable all interrupt sources on SPI bus
  for (SPI::Driver* dev = m_list; dev != NULL; dev = dev->m_next)
    if (dev->m_irq != NULL) dev->m_irq->disable();
  unlock(key);
}

void
SPI::release()
{
  // Lock the device driver update
  uint8_t key = lock();
  // Release the device driver
  m_busy = false;
  m_dev = NULL;
  // Enable all interrupt sources on SPI bus
  for (SPI::Driver* dev = m_list; dev != NULL; dev = dev->m_next)
    if (dev->m_irq != NULL) dev->m_irq->enable();
  unlock(key);
}

bool
SPI::attach(Driver* dev)
{
  if (dev->m_next != NULL) return (false);
  dev->m_next = m_list;
  m_list = dev;
  return (true);
}

uint8_t
SPI::transfer(uint8_t value)
{
  uint8_t bits = CHARBITS;
  if (m_dev->m_order == MSB_ORDER) {
    synchronized do {
      m_mosi._write(value & 0x80);
      m_sck._toggle();
      value <<= 1;
      if (m_miso.is_set()) value |= 0x01;
      m_sck._toggle();
    } while (--bits);
  }
  else {
    synchronized do {
      m_mosi._write(value & 0x01);
      m_sck._toggle();
      value >>= 1;
      if (m_miso.is_set()) value |= 0x80;
      m_sck._toggle();
    } while (--bits);
  }
  return (value);
}