Apple1-esp/pia.h

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C
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2014-11-17 20:00:40 +00:00
#ifndef __PIA_H__
#define __PIA_H__
class pia: public Memory::Device {
public:
pia(): Memory::Device(256), portb_cr(0), porta_cr(0) {}
virtual void reset() { portb_cr = porta_cr = 0; }
void operator=(byte);
operator byte();
void checkpoint(Stream &);
void restore(Stream &);
protected:
// write to the "external" side of the port
void set_porta(byte b) {
porta = b;
if (b & 0x80)
porta_cr = 0xa7;
}
// "device-side" operations (called from memory interface)
byte read_porta() { return porta; }
virtual byte read_porta_cr() {
if (porta_cr & 0x80) {
porta_cr = 0;
return 0xa7;
}
return porta_cr;
}
byte read_portb() { return portb; }
byte read_portb_cr() { return portb_cr; }
void write_porta(byte b) { porta = b; }
void write_porta_cr(byte b) {
if (!(porta_cr & 0x80) && b >= 0x80)
porta_cr |= 0x80;
else
porta_cr = b;
}
virtual void write_portb(byte b) { portb = b; }
void write_portb_cr(byte b) {
if (portb_cr < 0x80)
portb_cr = b;
}
private:
byte portb_cr, portb, porta_cr, porta;
};
#endif