fix(anchor): the chip-id halt names its cause and repeats it

crates/dsm-anchor-pico/src/main.rs

@@ -474,13 +474,18 @@ fn main() -> ! {
     // ---- Phase 1: raw link probe ~3s while USB enumerates ----
     let probe_until = timer.get_counter().ticks() + 3_000_000;
     let mut last = timer.get_counter();
+    // What the chip last put on MISO for the raw probe: the halt below reports
+    // it, so a silent bus (all 0x00 or all 0xFF) reads apart from a chip that
+    // answers but is refused.
+    let mut probe_rx = [0u8; 4];
     while timer.get_counter().ticks() < probe_until {
         usb_dev.poll(&mut [&mut serial]);
         if (timer.get_counter() - last).to_millis() >= 1000 {
             last = timer.get_counter();
             let mut rx = [0u8; 4];
             let tx = [0xAAu8, 0, 0, 0];
             let _ = spi_dev.transfer(&mut rx, &tx);
+            probe_rx = rx;
             let _ = serial.flush();
         }
     }
@@ -493,14 +498,22 @@ fn main() -> ! {
     let mut tropic = Tropic01::new(spi_dev);
     let chip_id_hash = match tropic.get_info_chip_id() {
         Ok(id) => anchor_core::hash::h("DSM/anchor/chip-id/v1", &[id]),
-        Err(_) => {
-            put(
-                &mut serial,
-                b"[T1] chip id: FAIL (no real identity; halting)\r\n",
+        Err(e) => {
+            // The halt names its cause, and repeats it: the banner is printed
+            // once at boot, before a phone or a Mac has attached to read it.
+            let why = alloc::format!(
+                "[T1] chip id: FAIL (no real identity; halting): {e:?}; raw probe MISO {probe_rx:?}\r\n"
             );
+            put(&mut serial, why.as_bytes());
             let _ = serial.flush();
+            let mut last = timer.get_counter();
             loop {
                 usb_dev.poll(&mut [&mut serial]);
+                if (timer.get_counter() - last).to_millis() >= 2000 {
+                    last = timer.get_counter();
+                    put(&mut serial, why.as_bytes());
+                    let _ = serial.flush();
+                }
             }
         }
     };