X-Git-Url: https://code.octet-stream.net/m17rt/blobdiff_plain/253c89360003ac72c4f7078c03af973c58a1b129..18349069c27a0b4fb2e39669fb535600805ad160:/m17core/src/tnc.rs?ds=sidebyside

diff --git a/m17core/src/tnc.rs b/m17core/src/tnc.rs
index 7851948..8cd0152 100644
--- a/m17core/src/tnc.rs
+++ b/m17core/src/tnc.rs
@@ -1,5 +1,7 @@
 use crate::address::{Address, Callsign};
-use crate::kiss::{KissBuffer, KissFrame, PORT_PACKET_BASIC, PORT_PACKET_FULL, PORT_STREAM};
+use crate::kiss::{
+    KissBuffer, KissCommand, KissFrame, PORT_PACKET_BASIC, PORT_PACKET_FULL, PORT_STREAM,
+};
 use crate::modem::ModulatorFrame;
 use crate::protocol::{
     Frame, LichCollection, LsfFrame, Mode, PacketFrame, PacketFrameCounter, StreamFrame,
@@ -22,6 +24,9 @@ pub struct SoftTnc {
     /// Latest state of data carrier detect from demodulator - controls whether we can go to TX
     dcd: bool,
 
+    /// If CSMA declined to transmit into an idle slot, at what point do we next check it?
+    next_csma_check: Option<u64>,
+
     /// Current monotonic time, counted in samples
     now: u64,
 
@@ -63,6 +68,12 @@ pub struct SoftTnc {
 
     /// Should PTT be on right now? Polled by external
     ptt: bool,
+
+    /// TxDelay raw value, number of 10ms units. We will optimistically start with default 0.
+    tx_delay: u8,
+
+    /// This is a full duplex channel so we do not need to monitor DCD or use CSMA. Default false.
+    full_duplex: bool,
 }
 
 impl SoftTnc {
@@ -72,6 +83,7 @@ impl SoftTnc {
             outgoing_kiss: None,
             state: State::Idle,
             dcd: false,
+            next_csma_check: None,
             now: 0,
             packet_queue: Default::default(),
             packet_next: 0,
@@ -83,6 +95,8 @@ impl SoftTnc {
             stream_curr: 0,
             stream_full: false,
             ptt: false,
+            tx_delay: 0,
+            full_duplex: false,
         }
     }
 
@@ -224,21 +238,56 @@ impl SoftTnc {
     pub fn read_tx_frame(&mut self) -> Option<ModulatorFrame> {
         match self.state {
             State::Idle | State::RxAcquiringStream(_) | State::RxStream(_) | State::RxPacket(_) => {
-                // We will let CSMA decide whether to actually go ahead.
-                // That's not implemented yet, so let's just check DCD.
-                let channel_free = !self.dcd;
                 let stream_wants_to_tx = self.stream_pending_lsf.is_some();
                 let packet_wants_to_tx = self.packet_full || (self.packet_next != self.packet_curr);
-                if channel_free && stream_wants_to_tx {
+                if !stream_wants_to_tx && !packet_wants_to_tx {
+                    return None;
+                }
+
+                // We have something we might send if the channel is free
+
+                // TODO: Proper full duplex support
+                // A true full duplex TNC should be able to rx and tx concurrently, implying
+                // separate states.
+                if !self.full_duplex {
+                    match self.next_csma_check {
+                        None => {
+                            if self.dcd {
+                                self.next_csma_check = Some(self.now + 1920);
+                                return None;
+                            } else {
+                                // channel is idle at the moment we get a frame to send
+                                // go right ahead
+                            }
+                        }
+                        Some(at_time) => {
+                            if self.now < at_time {
+                                return None;
+                            }
+                            // 25% chance that we'll transmit this slot.
+                            // Using self.now as random is probably fine so long as it's not being set in
+                            // a lumpy manner. m17app's soundmodem should be fine.
+                            // TODO: bring in prng to help in cases where `now` never ends in 0b11
+                            let p1_4 = (self.now & 3) == 3;
+                            if !self.dcd || !p1_4 {
+                                self.next_csma_check = Some(self.now + 1920);
+                                return None;
+                            } else {
+                                self.next_csma_check = None;
+                            }
+                        }
+                    }
+                }
+
+                if stream_wants_to_tx {
                     self.state = State::TxStream;
-                } else if channel_free && packet_wants_to_tx {
-                    self.state = State::TxPacket;
                 } else {
-                    return None;
+                    self.state = State::TxPacket;
                 }
                 self.ptt = true;
-                // TODO: true txdelay
-                Some(ModulatorFrame::Preamble { tx_delay: 0 })
+                Some(ModulatorFrame::Preamble {
+                    tx_delay: self.tx_delay,
+                })
             }
             State::TxStream => {
                 if !self.stream_full && self.stream_next == self.stream_curr {
@@ -316,6 +365,31 @@ impl SoftTnc {
             let Ok(port) = kiss_frame.port() else {
                 continue;
             };
+            let Ok(command) = kiss_frame.command() else {
+                continue;
+            };
+            if port != PORT_PACKET_BASIC && port != PORT_PACKET_FULL && port != PORT_STREAM {
+                continue;
+            }
+            if command == KissCommand::TxDelay {
+                let mut new_delay = [0u8; 1];
+                if kiss_frame.decode_payload(&mut new_delay) == Ok(1) {
+                    self.tx_delay = new_delay[0];
+                }
+                continue;
+            }
+            if command == KissCommand::FullDuplex {
+                let mut new_duplex = [0u8; 1];
+                if kiss_frame.decode_payload(&mut new_duplex) == Ok(1) {
+                    self.full_duplex = new_duplex[0] != 0;
+                }
+                continue;
+            }
+            if command != KissCommand::DataFrame {
+                // Not supporting any other settings yet
+                // TODO: allow adjusting P persistence parameter for CSMA
+                continue;
+            }
             if port == PORT_PACKET_BASIC {
                 if self.packet_full {
                     continue;