dp: Report optional master address as an Option

When a peripheral does not have a master it is tied to, then it reports
the master address 255.  Don't forward this implementation detail to the
user - instead report an untied peripheral with master address `None`.

examples/dp-scanner.rs

@@ -23,7 +23,6 @@ fn main() -> ! {
             .slot_bits(2500)
             // For generating the live-list as fast as possible, set GAP factor to 1.
             .gap_wait_rotations(1)
-            .max_retry_limit(3)
             .build(),
     );
     // We must not poll() too often or to little. T_slot / 2 seems to be a good compromise.
@@ -45,7 +44,7 @@ fn main() -> ! {
             Some(dp::scan::DpScanEvent::PeripheralFound(desc)) => {
                 log::info!("Discovered peripheral #{}:", desc.address);
                 log::info!("  - Ident: 0x{:04x}", desc.ident);
-                log::info!("  - Master: {:?}", desc.tied_to_master);
+                log::info!("  - Master: {:?}", desc.master_address);
             }
             Some(dp::scan::DpScanEvent::PeripheralLost(address)) => {
                 log::info!("Lost peripheral #{}.", address);

src/dp/peripheral.rs

@@ -95,7 +95,7 @@ pub struct PeripheralDiagnostics<'a> {
     /// This ident number must match the one passed in [`PeripheralOptions`].
     pub ident_number: u16,
     /// Address of the DP master this peripheral is locked to (if any)
-    pub master_address: u8,
+    pub master_address: Option<u8>,
     /// Extended diagnostics blocks
     pub extended_diagnostics: &'a crate::dp::ExtendedDiagnostics<'a>,
 }
@@ -105,7 +105,7 @@ pub struct PeripheralDiagnostics<'a> {
 pub(crate) struct DiagnosticsInfo {
     pub flags: DiagnosticFlags,
     pub ident_number: u16,
-    pub master_address: u8,
+    pub master_address: Option<u8>,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
@@ -640,11 +640,17 @@ impl<'a> Peripheral<'a> {
                 return None;
             }
 
+            let master_address = if t.pdu[3] == 255 {
+                None
+            } else {
+                Some(t.pdu[3])
+            };
+
             let mut diag = DiagnosticsInfo {
                 flags: DiagnosticFlags::from_bits_retain(u16::from_le_bytes(
                     t.pdu[0..2].try_into().unwrap(),
                 )),
-                master_address: t.pdu[3],
+                master_address,
                 ident_number: u16::from_be_bytes(t.pdu[4..6].try_into().unwrap()),
             };
 

src/dp/scan.rs

@@ -2,7 +2,7 @@
 pub struct DpPeripheralDescription {
     pub address: crate::Address,
     pub ident: u16,
-    pub tied_to_master: Option<crate::Address>,
+    pub master_address: Option<crate::Address>,
 }
 
 #[derive(Debug, PartialEq, Eq, Clone)]
@@ -46,11 +46,17 @@ impl DpScanner {
                 return None;
             }
 
+            let master_address = if t.pdu[3] == 255 {
+                None
+            } else {
+                Some(t.pdu[3])
+            };
+
             let mut diag = crate::dp::DiagnosticsInfo {
                 flags: crate::dp::DiagnosticFlags::from_bits_retain(u16::from_le_bytes(
                     t.pdu[0..2].try_into().unwrap(),
                 )),
-                master_address: t.pdu[3],
+                master_address,
                 ident_number: u16::from_be_bytes(t.pdu[4..6].try_into().unwrap()),
             };
 
@@ -128,8 +134,7 @@ impl crate::fdl::FdlApplication for DpScanner {
             let desc = DpPeripheralDescription {
                 address,
                 ident: diag.ident_number,
-                // TODO: Not always Some()
-                tied_to_master: Some(diag.master_address),
+                master_address: diag.master_address,
             };
 
             if station_unknown {