Merge pull request #3624 from dhalbert/usb-serial-detect-2

improve USB CDC disconnect/reconnect checking

Author: jepler

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

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
 }
 

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 )
     {