Implement more syscalls (#79)

This pull-request adds implementation of some trivial/simple/fake
BIOS syscalls.

cpm/cpm.go

@@ -370,6 +370,26 @@ func New(logger *slog.Logger, prn string) *CPM {
 		Handler: BiosSysCallPrintChar,
 		Fake:    true,
 	}
+	b[15] = CPMHandler{
+		Desc:    "LISTST",
+		Handler: BiosSysCallPrinterStatus,
+		Fake:    true,
+	}
+	b[17] = CPMHandler{
+		Desc:    "CONOST",
+		Handler: BiosSysCallScreenOutputStatus,
+		Fake:    true,
+	}
+	b[18] = CPMHandler{
+		Desc:    "AUXIST",
+		Handler: BiosSysCallAuxInputStatus,
+		Fake:    true,
+	}
+	b[19] = CPMHandler{
+		Desc:    "AUXOST",
+		Handler: BiosSysCallAuxOutputStatus,
+		Fake:    true,
+	}
 
 	// Create the emulator object and return it
 	tmp := &CPM{

cpm/cpm_bios.go

@@ -70,6 +70,46 @@ func BiosSysCallPrintChar(cpm *CPM) error {
 	return err
 }
 
+// BiosSysCallPrinterStatus returns status of current printer device.
+//
+// This is fake, and always returns "ready".
+func BiosSysCallPrinterStatus(cpm *CPM) error {
+
+	// Ready
+	cpm.CPU.States.AF.Hi = 0xFF
+	return nil
+}
+
+// BiosSysCallScreenOutputStatus returns status of current screen output device.
+//
+// This is fake, and always returns "ready".
+func BiosSysCallScreenOutputStatus(cpm *CPM) error {
+
+	// Ready
+	cpm.CPU.States.AF.Hi = 0xFF
+	return nil
+}
+
+// BiosSysCallAuxInputStatus returns status of current auxiliary input device.
+//
+// This is fake, and always returns "ready".
+func BiosSysCallAuxInputStatus(cpm *CPM) error {
+
+	// Ready
+	cpm.CPU.States.AF.Hi = 0xFF
+	return nil
+}
+
+// BiosSysCallAuxOutputStatus returns status of current auxiliary output device.
+//
+// This is fake, and always returns "ready".
+func BiosSysCallAuxOutputStatus(cpm *CPM) error {
+
+	// Ready
+	cpm.CPU.States.AF.Hi = 0xFF
+	return nil
+}
+
 // BiosHandler is involved when a BIOS syscall needs to be executed,
 // which is handled via a small trampoline.
 //

main.go

@@ -66,7 +66,7 @@ func main() {
 
 		// Now show them.
 		fmt.Printf("BDOS\n")
-		for id := range ids {
+		for _, id := range ids {
 			ent := c.BDOSSyscalls[uint8(id)]
 			fake := ""
 			if ent.Fake {
@@ -84,7 +84,7 @@ func main() {
 
 		// Now show them.
 		fmt.Printf("BIOS\n")
-		for id := range ids {
+		for _, id := range ids {
 			ent := c.BIOSSyscalls[uint8(id)]
 			fake := ""
 			if ent.Fake {