i6502/acia6551.go

package i6502

import "fmt"

const (
	aciaData = iota
	aciaStatus
	aciaCommand
	aciaControl
)

/*
ACIA 6551 Serial IO

This Asynchronous Communications Interface Adapater can be
directly attached to the 6502's address and data busses.

It provides serial IO.

The supplied Rx and Tx channels can be used to read and wirte
data to the ACIA 6551.
*/
type Acia6551 struct {
	Rx chan byte // Reading (Acia Input) line
	Tx chan byte // Transmitting (Acia Output) line

	rxData byte
	txData byte

	commandData byte
	controlData byte

	rxFull  bool
	txEmpty bool

	rxIrqEnabled bool
	txIrqEnabled bool

	overrun bool
}

func NewAcia6551(rx chan byte, tx chan byte) (*Acia6551, error) {
	acia := &Acia6551{Tx: tx, Rx: rx}
	acia.Reset()

	go func() {
		for {
			select {
			case data := <-acia.Rx:
				acia.rxData = data
				acia.rxFull = true
				fmt.Printf("Rx: 0x%02X\n", data)
			}
		}
	}()

	go func() {
		// Handle tx data channel
	}()

	return acia, nil
}

func (a *Acia6551) Size() uint16 {
	// We have a only 4 addresses, Data, Status, Command and Control
	return 0x04
}

// Emulates a hardware reset
func (a *Acia6551) Reset() {
	a.rxData = 0
	a.rxFull = false

	a.txData = 0
	a.txEmpty = true

	a.rxIrqEnabled = false
	a.txIrqEnabled = false

	a.overrun = false

	a.setControl(0)
	a.setCommand(0)
}

func (a *Acia6551) setControl(data byte) {
}

func (a *Acia6551) setCommand(data byte) {
}

// Used by the AddressBus to read data from the ACIA 6551
func (a *Acia6551) Read(address uint16) byte {
	switch address {
	case aciaData:
		// Read Rx
	case aciaStatus:
		// Read Status reg.
	case aciaCommand:
		// Read command
	case aciaControl:
		// Read control
	}

	return 0x00
}

func (a *Acia6551) Write(address uint16, data byte) {
	switch address {
	case aciaData:
		// Write Tx
	case aciaStatus:
		// Reset
	case aciaCommand:
		// Write command
	case aciaControl:
		// Write control
	}
}