use crate::decode::{
parse_lsf, parse_packet, parse_stream, sync_burst_correlation, SyncBurst, SYNC_THRESHOLD,
};
+use crate::encode::{
+ encode_lsf, encode_packet, encode_stream, generate_end_of_transmission, generate_preamble,
+};
use crate::protocol::{Frame, LsfFrame, PacketFrame, StreamFrame};
use crate::shaping::RRC_48K;
use log::debug;
/// Furthermore we attempt to track and account for the latency between the output
/// soundcard callback, and when those samples will actually be on the wire. CPAL helpfully
/// gives us an estimate. The latest estimate of latency is converted to a duration in terms
- /// of number of samples and provided as `output_latency`.
- ///
- /// Finally, we give the modem a monotonic timer expressed in the number of samples of time
- /// that have elapsed since the modem began operation. When the modulator advises the TNC
- /// exactly when a transmission is expected to complete, it should be expressed in terms of
- /// this number.
+ /// of number of samples and provided as `output_latency`. Added to this is the current
+ /// number of samples we expect remain to be processed from the last read.
///
- /// Call this whenever bytes have been read out of the buffer, or the TNC may have something
- /// new to send.
+ /// Call this whenever bytes have been read out of the buffer.
fn update_output_buffer(
&mut self,
samples_to_play: usize,
capacity: usize,
output_latency: usize,
- now_samples: u64,
);
/// Supply the next frame available from the TNC, if it was requested.
- fn next_frame(&mut self, frame: Option<ModulatorFrame>);
+ fn provide_next_frame(&mut self, frame: Option<ModulatorFrame>);
/// Calculate and write out output samples for the soundcard.
///
/// Modulator wishes to send samples to the output buffer - call `read_output_samples`.
ReadOutput,
- /// Advise the TNC that we will complete sending End Of Transmission at the given time and
- TransmissionWillEnd(u64),
+ /// Advise the TNC that we will complete sending End Of Transmission after the given number of
+ /// samples has elapsed, and therefore PTT should be deasserted at this time.
+ TransmissionWillEnd(usize),
}
/// Frames for transmission, emitted by the TNC and received by the Modulator.
EndOfTransmission,
}
-struct SoftModulator {
- /// Next modulated frame to output - 1920 samples for 40ms frame plus 80 for ramp-up/ramp-down
+pub struct SoftModulator {
+ /// Next modulated frame to output - 1920 samples for 40ms frame plus 80 for ramp-down
next_transmission: [i16; 2000],
/// How much of next_transmission should in fact be transmitted
next_len: usize,
/// What is that idle status?
idle: bool,
- /// Do we need to report that a transmission end time? (True after we encoded an EOT)
- report_tx_end: bool,
- /// What will that end time be?
- tx_end_time: u64,
+ /// Do we need to calculate a transmission end time?
+ ///
+ /// (True after we encoded an EOT.) We will wait until we get a precise timing update.
+ calculate_tx_end: bool,
+ /// Do we need to report a transmission end time?
+ ///
+ /// This is a duration expressed in number of samples.
+ report_tx_end: Option<usize>,
- /// Circular buffer of incoming samples for calculating the RRC filtered value
- filter_win: [i16; 81],
+ /// Circular buffer of most recently output samples for calculating the RRC filtered value.
+ ///
+ /// This should naturally degrade to an oldest value plus 80 zeroes after an EOT.
+ filter_win: [f32; 81],
/// Current position in filter_win
filter_cursor: usize,
/// Should we ask the TNC for another frame. True after each call to update_output_buffer.
try_get_frame: bool,
- now: u64,
+ /// Expected delay beyond the buffer to reach the DAC
output_latency: usize,
+ /// Number of samples we have placed in the buffer for the output soundcard not yet picked up.
samples_in_buf: usize,
+ /// Total size to which the output buffer is allowed to expand.
buf_capacity: usize,
}
+impl SoftModulator {
+ pub fn new() -> Self {
+ Self {
+ next_transmission: [0i16; 2000],
+ next_len: 0,
+ next_read: 0,
+ tx_delay_padding: 0,
+ update_idle: true,
+ idle: true,
+ calculate_tx_end: false,
+ report_tx_end: None,
+ filter_win: [0f32; 81],
+ filter_cursor: 0,
+ try_get_frame: false,
+ output_latency: 0,
+ samples_in_buf: 0,
+ buf_capacity: 0,
+ }
+ }
+
+ fn push_sample(&mut self, dibit: f32) {
+ // Right now we are encoding everything as 1.0-scaled dibit floats
+ // This is a bit silly but it will do for a minute
+ // Max theoretical gain from the RRC filter is 4.328
+ // Let's bump everything to a baseline of 16383 / 4.328 = 3785.35
+ // This is not particularly high but at least we won't ever hit the top
+ self.filter_win[self.filter_cursor] = dibit * 3785.0;
+ self.filter_cursor = (self.filter_cursor + 1) % 81;
+ let mut out: f32 = 0.0;
+ for i in 0..81 {
+ let filter_idx = (self.filter_cursor + i) % 81;
+ out += RRC_48K[i] * self.filter_win[filter_idx];
+ }
+ self.next_transmission[self.next_len] = out as i16;
+ self.next_len += 1;
+ }
+
+ fn request_frame_if_space(&mut self) {
+ if self.buf_capacity - self.samples_in_buf >= 2000 {
+ self.try_get_frame = true;
+ }
+ }
+}
+
impl Modulator for SoftModulator {
fn update_output_buffer(
&mut self,
samples_to_play: usize,
capacity: usize,
output_latency: usize,
- now_samples: u64,
) {
- self.now = now_samples;
self.output_latency = output_latency;
self.buf_capacity = capacity;
self.samples_in_buf = samples_to_play;
- if capacity - samples_to_play >= 2000 {
- self.try_get_frame = true;
+ if self.calculate_tx_end {
+ self.calculate_tx_end = false;
+ // next_transmission should already have been read out to the buffer by now
+ // so we don't have to consider it
+ self.report_tx_end = Some(self.samples_in_buf + self.output_latency);
}
+
+ self.request_frame_if_space();
}
- fn next_frame(&mut self, frame: Option<ModulatorFrame>) {
+ fn provide_next_frame(&mut self, frame: Option<ModulatorFrame>) {
+ let Some(frame) = frame else {
+ self.try_get_frame = false;
+ return;
+ };
+
+ self.next_len = 0;
+ self.next_read = 0;
+
match frame {
- Some(_f) => {}
- None => {
- self.try_get_frame = false;
+ ModulatorFrame::Preamble { tx_delay } => {
+ // TODO: Stop assuming 48 kHz everywhere. 24 kHz should be fine too.
+ let tx_delay_samples = tx_delay as usize * 480;
+ // TxDelay and output latency have the same effect - account for whichever is bigger.
+ // We want our sound card DAC hitting preamble right when PTT fully engages.
+ // The modulator calls the shots here - TNC hands over Preamble and asserts PTT, then
+ // waits to be told when transmission will be complete. This estimate will not be
+ // made and delivered until we generate the EOT frame.
+ self.tx_delay_padding = tx_delay_samples.max(self.output_latency);
+
+ // We should be starting from a filter_win of zeroes
+ // Transmission is effectively smeared by 80 taps and we'll capture that in EOT
+ for dibit in generate_preamble() {
+ self.push_sample(dibit);
+ }
+ }
+ ModulatorFrame::Lsf(lsf_frame) => {
+ for dibit in encode_lsf(&lsf_frame) {
+ self.push_sample(dibit);
+ }
+ }
+ ModulatorFrame::Stream(stream_frame) => {
+ for dibit in encode_stream(&stream_frame) {
+ self.push_sample(dibit);
+ }
+ }
+ ModulatorFrame::Packet(packet_frame) => {
+ for dibit in encode_packet(&packet_frame) {
+ self.push_sample(dibit);
+ }
+ }
+ ModulatorFrame::EndOfTransmission => {
+ for dibit in generate_end_of_transmission() {
+ self.push_sample(dibit);
+ }
+ for _ in 0..80 {
+ // This is not a real symbol value
+ // However we want to flush the filter
+ self.push_sample(0f32);
+ }
+ self.calculate_tx_end = true;
}
}
-
- // this is where we write it to next_transmission
-
- // this is where we set report_tx_end
- todo!()
}
fn read_output_samples(&mut self, out: &mut [i16]) -> usize {
}
fn run(&mut self) -> Option<ModulatorAction> {
+ // Time-sensitive for accuracy, so handle it first
+ if let Some(end) = self.report_tx_end.take() {
+ return Some(ModulatorAction::TransmissionWillEnd(end));
+ }
+
if self.next_read < self.next_len {
return Some(ModulatorAction::ReadOutput);
}
return Some(ModulatorAction::SetIdle(self.idle));
}
- if self.report_tx_end {
- self.report_tx_end = false;
- return Some(ModulatorAction::TransmissionWillEnd(self.tx_end_time));
- }
-
if self.try_get_frame {
return Some(ModulatorAction::GetNextFrame);
}
projects / m17rt / blobdiff