From 345d84ffde527b16f50c203f7b6a718886be34f6 Mon Sep 17 00:00:00 2001
From: Dan Halbert <halbert@halwitz.org>
Date: Fri, 30 Oct 2020 22:16:12 -0400
Subject: [PATCH] improve USB CDC disconnect/reconnect checking

---
 supervisor/serial.h         | 1 -
 supervisor/shared/serial.c  | 6 +++---
 supervisor/shared/usb/usb.c | 3 ---
 3 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/supervisor/serial.h b/supervisor/serial.h
index 9c2d44737a..066886303e 100644
--- a/supervisor/serial.h
+++ b/supervisor/serial.h
@@ -47,5 +47,4 @@ char serial_read(void);
 bool serial_bytes_available(void);
 bool serial_connected(void);
 
-extern volatile bool _serial_connected;
 #endif  // MICROPY_INCLUDED_SUPERVISOR_SERIAL_H
diff --git a/supervisor/shared/serial.c b/supervisor/shared/serial.c
index 91e90671d2..7383cc2282 100644
--- a/supervisor/shared/serial.c
+++ b/supervisor/shared/serial.c
@@ -47,8 +47,6 @@ busio_uart_obj_t debug_uart;
 byte buf_array[64];
 #endif
 
-volatile bool _serial_connected;
-
 void serial_early_init(void) {
 #if defined(DEBUG_UART_TX) && defined(DEBUG_UART_RX)
     debug_uart.base.type = &busio_uart_type;
@@ -71,7 +69,9 @@ bool serial_connected(void) {
 #if defined(DEBUG_UART_TX) && defined(DEBUG_UART_RX)
     return true;
 #else
-    return _serial_connected;
+    // True if DTR is asserted, and the USB connection is up.
+    // tud_cdc_get_line_state(): bit 0 is DTR, bit 1 is RTS
+    return (tud_cdc_get_line_state() & 1) && tud_ready();
 #endif
 }
 
diff --git a/supervisor/shared/usb/usb.c b/supervisor/shared/usb/usb.c
index 89fbf56f37..93d3436e9d 100644
--- a/supervisor/shared/usb/usb.c
+++ b/supervisor/shared/usb/usb.c
@@ -116,7 +116,6 @@ void tud_umount_cb(void) {
 // remote_wakeup_en : if host allows us to perform remote wakeup
 // USB Specs: Within 7ms, device must draw an average current less than 2.5 mA from bus
 void tud_suspend_cb(bool remote_wakeup_en) {
-    _serial_connected = false;
 }
 
 // Invoked when usb bus is resumed
@@ -128,8 +127,6 @@ void tud_resume_cb(void) {
 void tud_cdc_line_state_cb(uint8_t itf, bool dtr, bool rts) {
     (void) itf; // interface ID, not used
 
-    _serial_connected = dtr;
-
     // DTR = false is counted as disconnected
     if ( !dtr )
     {