ph00524: add emulator

modules/ph00524/emu/i8255.go

@@ -0,0 +1,102 @@
+package main
+
+import "log"
+
+// i8255 is a generic Intel 8255-compatible I/O controller chip.
+//
+// Only mode 0 is supported.
+type i8255 struct {
+	pa, pb, pc uint8
+
+	onOut func(port i8255Port)
+	onIn  func(port i8255Port)
+}
+
+type i8255Port string
+
+const (
+	PA i8255Port = "PA"
+	PB i8255Port = "PB"
+	PC i8255Port = "PC"
+)
+
+func (i *i8255) getPort(p i8255Port) uint8 {
+	switch p {
+	case PA:
+		return i.pa
+	case PB:
+		return i.pb
+	case PC:
+		return i.pc
+	default:
+		log.Fatalf("invalid port")
+		return 0
+	}
+}
+
+func (i *i8255) Out(addr, value uint8) {
+	switch addr {
+	case 0:
+		i.pa = value
+		if i.onOut != nil {
+			i.onOut(PA)
+		}
+	case 1:
+		i.pb = value
+		if i.onOut != nil {
+			i.onOut(PB)
+		}
+	case 2:
+		i.pc = value
+		if i.onOut != nil {
+			i.onOut(PC)
+		}
+	case 3:
+		if (value >> 7) == 0 {
+			// BSR mode
+			bitno := (value >> 1) & 0b111
+			bitval := value & 1
+			if bitval == 1 {
+				i.pc |= (1 << bitno)
+			} else {
+				i.pc &= 0xff ^ (1 << bitno)
+			}
+		} else {
+			// Input/Output mode
+			gaMode := (value >> 5) & 0b11
+			gbMode := (value >> 5) & 0b11
+			if gaMode != 0 {
+				log.Fatalf("I8255 implementation only supports mode 0 on Port A")
+			}
+			if gbMode != 0 {
+				log.Fatalf("I8255 implementation only supports mode 0 on Port B")
+			}
+			// Don't care about the rest (input/output settings per group/port).
+		}
+	default:
+		log.Printf("I8255: invalid out")
+	}
+}
+
+func (i *i8255) In(addr uint8) uint8 {
+	switch addr {
+	case 0:
+		if i.onIn != nil {
+			i.onIn(PA)
+		}
+		return i.pa
+	case 1:
+		if i.onIn != nil {
+			i.onIn(PB)
+		}
+		return i.pb
+	case 2:
+		if i.onIn != nil {
+			i.onIn(PC)
+		}
+		return i.pc
+	default:
+		log.Printf("I8255: invalid in")
+		return 0
+	}
+}