Halt and detach target if host releases DTR.

Port reads 0x04 (EOF) when DTR is released.  GDB loop detaches from
target if EOF is read.
Fixes bug 3307433.

src/gdb_main.c

@@ -151,11 +151,13 @@ gdb_main(void)
 			}
 
 			/* Wait for target halt */
-			while(!target_halt_wait(cur_target)) 
-				if(gdb_if_getchar_to(0) == '\x03') {
+			while(!target_halt_wait(cur_target)) { 
+				unsigned char c = gdb_if_getchar_to(0);
+				if((c == '\x03') || (c == '\x04')) {
 					target_halt_request(cur_target);
 					sent_int = 1;
 				}
+			}
 
 			SET_RUN_STATE(0);
 			/* Report reason for halt */

src/stm32/cdcacm.c

@@ -46,6 +46,7 @@
 static char *get_dev_unique_id(char *serial_no);
 
 static int configured;
+static int cdcacm_gdb_dtr;
 
 static const struct usb_device_descriptor dev = {
         .bLength = USB_DT_DEVICE_SIZE,
@@ -346,9 +347,12 @@ static int cdcacm_control_request(struct usb_setup_data *req, uint8_t **buf,
 
 	switch(req->bRequest) {
 	case USB_CDC_REQ_SET_CONTROL_LINE_STATE: 
-		/* This Linux cdc_acm driver requires this to be implemented 
-		 * even though it's optional in the CDC spec, and we don't 
-		 * advertise it in the ACM functional descriptor. */
+		/* Ignore if not for GDB interface */
+		if(req->wIndex != 0)
+			return 1;
+
+		cdcacm_gdb_dtr = req->wValue & 1;
+
 		return 1;
 #ifdef INCLUDE_UART_INTERFACE
 	case USB_CDC_REQ_SET_LINE_CODING: {
@@ -402,6 +406,11 @@ int cdcacm_get_config(void)
 	return configured;
 }
 
+int cdcacm_get_dtr(void)
+{
+	return cdcacm_gdb_dtr;
+}
+
 #ifdef INCLUDE_UART_INTERFACE
 static void cdcacm_data_rx_cb(u8 ep)
 {

src/stm32/gdb_if.c

@@ -47,6 +47,10 @@ void gdb_if_putchar(unsigned char c, int flush)
 unsigned char gdb_if_getchar(void)
 {
 	while(!(out_ptr < count_out)) {
+		/* Detach if port closed */
+		if(!cdcacm_get_dtr())
+			return 0x04;
+
 		while(cdcacm_get_config() != 1);
 		count_out = usbd_ep_read_packet(1, buffer_out, 
 					VIRTUAL_COM_PORT_DATA_SIZE);
@@ -61,6 +65,10 @@ unsigned char gdb_if_getchar_to(int timeout)
 	timeout_counter = timeout/100;
 
 	if(!(out_ptr < count_out)) do {
+		/* Detach if port closed */
+		if(!cdcacm_get_dtr())
+			return 0x04;
+
 		count_out = usbd_ep_read_packet(1, buffer_out, 
 					VIRTUAL_COM_PORT_DATA_SIZE);
 		out_ptr = 0;

src/stm32/platform.c

@@ -28,6 +28,7 @@
 #include <libopencm3/stm32/scb.h>
 #include <libopencm3/stm32/nvic.h>
 #include <libopencm3/stm32/usart.h>
+#include <libopencm3/usb/usbd.h>
 
 #include "platform.h"
 #include "jtag_scan.h"

src/stm32/platform.h

@@ -124,6 +124,7 @@ void morse(const char *msg, char repeat);
 void cdcacm_init(void);
 /* Returns current usb configuration, or 0 if not configured. */
 int cdcacm_get_config(void);
+int cdcacm_get_dtr(void);
 
 /* Use newlib provided integer only stdio functions */
 #define sscanf siscanf