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fix(mesh): deassert DTR/RTS before serial probes to avoid ESP32-S3 native-USB resets

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Heltec V3/V4-class boards use the ESP32-S3's native USB-Serial-JTAG
peripheral (no discrete USB-UART bridge chip), which resets the chip on a
DTR/RTS transition — the same mechanism esptool uses to force bootloader
entry. The Meshcore/Meshtastic/RNode serial probes all open the port with
library defaults (DTR/RTS asserted), so each probe attempt was likely
rebooting a real, correctly RNode-flashed Heltec board mid-handshake,
surfacing as an endless "No supported mesh radio found" retry loop.

Deassert both lines immediately after open and let the board settle before
writing, in all three probe paths.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
This commit is contained in:
ssmithx 2026-07-04 01:28:23 +00:00
parent 7f657ab099
commit 9bbbb046a8
3 changed files with 20 additions and 0 deletions
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6
core/archipelago/src/mesh/meshtastic.rs
View File

@ -180,6 +180,12 @@ impl MeshtasticDevice {
"Failed to open serial port {} (permission denied? device busy?)", "Failed to open serial port {} (permission denied? device busy?)",
path path
))?; ))?;
// See probe_rnode() in reticulum.rs for why: ESP32-S3 native-USB
// boards reset on a DTR/RTS transition, so deassert both and settle
// before the handshake below.
let _ = port.set_dtr(false);
let _ = port.set_rts(false);
tokio::time::sleep(Duration::from_millis(300)).await;
info!(path = %path, baud = BAUD_RATE, "Opened Meshtastic serial port"); info!(path = %path, baud = BAUD_RATE, "Opened Meshtastic serial port");
Ok(Self { Ok(Self {

8
core/archipelago/src/mesh/reticulum.rs
View File

@ -1005,6 +1005,14 @@ fn parse_hash16(hex_str: &str) -> Result<[u8; 16]> {
async fn probe_rnode(path: &str) -> Result<()> { async fn probe_rnode(path: &str) -> Result<()> {
let port = serial2_tokio::SerialPort::open(path, PROBE_BAUD) let port = serial2_tokio::SerialPort::open(path, PROBE_BAUD)
.with_context(|| format!("Failed to open {} for Reticulum probe", path))?; .with_context(|| format!("Failed to open {} for Reticulum probe", path))?;
// ESP32-S3 native-USB boards (Heltec V3/V4 etc. — no separate USB-UART
// bridge chip) treat a DTR/RTS transition on open as a reset signal, the
// same mechanism esptool uses to force bootloader entry. Deassert both
// and let the board settle before writing the probe, or the reboot eats
// the DETECT_RESP window below.
let _ = port.set_dtr(false);
let _ = port.set_rts(false);
tokio::time::sleep(Duration::from_millis(300)).await;
let probe: [u8; 13] = [ let probe: [u8; 13] = [
KISS_FEND, KISS_FEND,
KISS_CMD_DETECT, KISS_CMD_DETECT,

6
core/archipelago/src/mesh/serial.rs
View File

@ -57,6 +57,12 @@ impl MeshcoreDevice {
"Failed to open serial port {} (permission denied? device busy?)", "Failed to open serial port {} (permission denied? device busy?)",
path path
))?; ))?;
// See probe_rnode() in reticulum.rs for why: ESP32-S3 native-USB
// boards reset on a DTR/RTS transition, so deassert both and settle
// before the handshake below.
let _ = port.set_dtr(false);
let _ = port.set_rts(false);
tokio::time::sleep(Duration::from_millis(300)).await;
info!(path = %path, baud = BAUD_RATE, "Opened serial port"); info!(path = %path, baud = BAUD_RATE, "Opened serial port");