PCF8574.h

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#ifndef PCF8574_H
#define PCF8574_H

#include "TWI.h"

class PCF8574 : protected TWI::Device {
public:
  PCF8574(TWI& twi, uint8_t subaddr = 7) :
    TWI::Device(twi, 0x20 | (subaddr & 0x7)),
    m_ddr(0xff),
    m_port(0)
  {}

  uint8_t ddr()
  {
    return (m_ddr);
  }

  void ddr(uint8_t ddr)
  {
    m_ddr = ddr;
    m_port |= m_ddr;
    acquire();
    Device::write(&m_port, sizeof(m_port));
    release();
  }

  uint8_t read()
  {
    uint8_t res;
    acquire();
    Device::read(&res, sizeof(res));
    release();
    return ((res & m_ddr) | m_port);
  }

  uint8_t port()
  {
    return (m_port);
  }

  void write(uint8_t value)
  {
    acquire();
    m_port = value | m_ddr;
    Device::write(&m_port, sizeof(m_port));
    release();
  }

  void write(void* buf, size_t size)
  {
    acquire();
    uint8_t* bp = (uint8_t*) buf;
    size_t n = size;
    while (n--) *bp++ |= m_ddr;
    Device::write(buf, size);
    release();
  }

  template<uint8_t PIN>
  class GPIO {
  public:
    static const uint8_t MASK = (1 << (PIN & 0x7));

    GPIO(PCF8574& dev) : m_dev(dev) {}

    void input()
      __attribute__((always_inline))
    {
      m_dev.ddr(m_dev.ddr() | MASK);
    }

    void output()
      __attribute__((always_inline))
    {
      m_dev.ddr(m_dev.ddr() & ~MASK);
    }

    bool read()
    {
      if (m_dev.ddr() & MASK)
        return ((m_dev.read() & MASK) != 0);
      return ((m_dev.port() & MASK) != 0);
    }

    operator bool()
      __attribute__((always_inline))
    {
      return (read());
    }

    void write(int value)
    {
      uint8_t data = m_dev.port();
      if (value)
        data |= MASK;
      else
        data &= ~MASK;
      m_dev.write(data);
    }

    void operator=(int value)
      __attribute__((always_inline))
    {
      write(value);
    }

  protected:
    PCF8574& m_dev;
  };

protected:
  uint8_t m_ddr;

  uint8_t m_port;

  PCF8574(TWI& twi, uint8_t addr, uint8_t subaddr) :
    TWI::Device(twi, addr | (subaddr & 0x7)),
    m_ddr(0xff),
    m_port(0)
  {}
};

class PCF8574A : public PCF8574 {
public:
  PCF8574A(TWI& twi, uint8_t subaddr = 7) : PCF8574(twi, 0x38, subaddr) {}
};
#endif