Sort of working version

No integration with Wallas Heater itself, but boots
and connects to preconfigured Wifi - fetches time and
can display HTML pages.

src/sntp_client.rs

@@ -0,0 +1,99 @@
+
+use core::net::{IpAddr, SocketAddr};
+use embassy_net::Stack;
+use embassy_net::dns::DnsQueryType;
+use embassy_time::{Duration, Instant, Timer};
+use embassy_net::udp::{PacketMetadata, UdpSocket};
+use embassy_sync::watch::Watch;
+use embassy_sync::blocking_mutex::raw::CriticalSectionRawMutex;
+use alloc::string::String;
+
+use log::error;
+use sntpc::{get_time, NtpContext, NtpTimestampGenerator};
+use chrono::{DateTime, Utc};
+
+#[derive(Copy, Clone)]
+struct Timestamp {
+    tstamp: Instant,
+}
+
+static UTC_DATETIME: Watch<CriticalSectionRawMutex, Duration, 2> = Watch::new(); 
+
+pub fn get_now() -> String {
+    let offset = UTC_DATETIME.try_get();
+    match offset {
+        None => {
+           alloc::format!("LAUNCH+{}s", Instant::now().as_secs())
+        },
+        Some(duration) => {
+            let now = Instant::now() + duration;
+            let micros: i64 = now.as_micros() as i64;
+            let dt = DateTime::<Utc>::from_timestamp_micros(micros);
+            match dt {
+                Some(val) => alloc::format!("{}", val.format("%Y-%m-%d %H:%M:%S")),
+                None => alloc::format!("LAUNCH+{}s", Instant::now().as_secs())
+            }
+        }
+    }
+}
+
+
+impl NtpTimestampGenerator for Timestamp {
+    fn init(&mut self) {
+        self.tstamp = Instant::now();
+    }
+
+    fn timestamp_sec(&self) -> u64 {
+        self.tstamp.as_secs()
+    }
+
+    fn timestamp_subsec_micros(&self) -> u32 {
+        (self.tstamp.as_micros() % 1_000_000) as u32
+    }
+}
+
+pub fn sntp_client_spawn(spawner: embassy_executor::Spawner, stack: Stack<'static>) {
+    
+   spawner.must_spawn(sntp_client(stack));
+}
+
+#[embassy_executor::task]
+async fn sntp_client(stack: Stack<'static>) {
+
+    // Create UDP socket
+    let mut rx_meta = [PacketMetadata::EMPTY; 16];
+    let mut rx_buffer = [0; 4096];
+    let mut tx_meta = [PacketMetadata::EMPTY; 16];
+    let mut tx_buffer = [0; 4096];
+
+    let mut socket = UdpSocket::new(stack, &mut rx_meta, &mut rx_buffer, &mut tx_meta, &mut tx_buffer);
+    socket.bind(123).unwrap();
+
+    let context = NtpContext::new(Timestamp{tstamp: Instant::now()});
+    let server_list : alloc::vec::Vec<&str> = alloc::vec!["0.pool.ntp.org", "1.pool.ntp.org", "2.pool.ntp.org", "3.pool.ntp.org"];
+    let mut current_server = 2;
+
+    let sender = UTC_DATETIME.sender();
+
+    loop {
+        let dns_res = stack.dns_query  (server_list[current_server], DnsQueryType::A).await.expect("Failed to resolve NTP server");
+        let addr: IpAddr = dns_res[0].into();
+        let result =
+            get_time(SocketAddr::from((addr, 123)), &socket, context).await;
+
+        match result {
+            Ok(time) => {
+                let offset = Duration::from_micros(time.offset as u64);
+                sender.send(offset);
+                Timer::after(Duration::from_secs(7*24*3600)).await;  // redo SNTP check in a week
+            }
+            Err(e) => {
+                error!("Error getting time: {:?}", e);
+                current_server = (current_server + 1) % 4;
+                Timer::after(Duration::from_secs(30)).await;
+            }
+        }
+
+    }
+}
+

src/static/styles.css

@@ -0,0 +1,22 @@
+body {
+  font-family: serif;
+  text-align: center;
+  color: #321C0B;
+  background-color: #D5E4F6;
+  height: 100%;
+}
+h1 {
+  color: #B15C1B;
+}
+h4 {
+  color: #2969B2;
+}
+p.intro {
+  border: 1px solid #B15C1B;
+  padding: 0.2em;
+  margin: 0.3em 10vw 0.3em 10vw;
+}
+div#footer {
+    position: absolute;
+    bottom: 0px;
+}