103 lines
1.6 KiB
Go
103 lines
1.6 KiB
Go
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package main
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import "log"
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// i8255 is a generic Intel 8255-compatible I/O controller chip.
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//
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// Only mode 0 is supported.
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type i8255 struct {
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pa, pb, pc uint8
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onOut func(port i8255Port)
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onIn func(port i8255Port)
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}
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type i8255Port string
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const (
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PA i8255Port = "PA"
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PB i8255Port = "PB"
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PC i8255Port = "PC"
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)
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func (i *i8255) getPort(p i8255Port) uint8 {
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switch p {
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case PA:
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return i.pa
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case PB:
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return i.pb
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case PC:
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return i.pc
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default:
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log.Fatalf("invalid port")
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return 0
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}
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}
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func (i *i8255) Out(addr, value uint8) {
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switch addr {
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case 0:
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i.pa = value
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if i.onOut != nil {
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i.onOut(PA)
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}
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case 1:
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i.pb = value
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if i.onOut != nil {
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i.onOut(PB)
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}
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case 2:
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i.pc = value
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if i.onOut != nil {
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i.onOut(PC)
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}
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case 3:
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if (value >> 7) == 0 {
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// BSR mode
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bitno := (value >> 1) & 0b111
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bitval := value & 1
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if bitval == 1 {
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i.pc |= (1 << bitno)
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} else {
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i.pc &= 0xff ^ (1 << bitno)
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}
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} else {
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// Input/Output mode
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gaMode := (value >> 5) & 0b11
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gbMode := (value >> 5) & 0b11
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if gaMode != 0 {
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log.Fatalf("I8255 implementation only supports mode 0 on Port A")
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}
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if gbMode != 0 {
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log.Fatalf("I8255 implementation only supports mode 0 on Port B")
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}
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// Don't care about the rest (input/output settings per group/port).
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}
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default:
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log.Printf("I8255: invalid out")
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}
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}
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func (i *i8255) In(addr uint8) uint8 {
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switch addr {
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case 0:
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if i.onIn != nil {
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i.onIn(PA)
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}
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return i.pa
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case 1:
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if i.onIn != nil {
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i.onIn(PB)
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}
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return i.pb
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case 2:
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if i.onIn != nil {
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i.onIn(PC)
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}
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return i.pc
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default:
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log.Printf("I8255: invalid in")
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return 0
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}
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}
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