monitor: Add support for reading over J-Link RTT

This patch adds support for reading data over J-Link RTT. It can be
used as replacement for TTY when reading from embedded devices since
it's much faster and does block a UART. Data format is the same as
for TTY. At the moment monitor over RTT is only supported by Apache
Mynewt project.

Reading data is done by polling RTT every 1 msec since there is no
blocking API to read something from RTT buffer.

To enable reading from RTT, J-Link configuration needs to be passed via
command line (all parameters except <device> can be skipped to use
default value):
  -J <device>,<serialno=0>,<interface=swd>,<speed=1000>
  -J nrf52,683649029

In some cases J-Link cannot locate RTT buffer in RAM. In such case
RAM area and buffer name should be provided via command line:
  -R <address=0x0>,<area=0x1000>,<buffer=monitor>
  -R 0x20000000,0x10000

1 files changed, 50 insertions, 0 deletions

diff --git a/monitor/control.c b/monitor/control.c
index 4022e7644..1e9054db3 100644
--- a/monitor/control.c
+++ b/monitor/control.c
@@ -57,6 +57,7 @@
 #include "ellisys.h"
 #include "tty.h"
 #include "control.h"
+#include "jlink.h"
 
 static struct btsnoop *btsnoop_file = NULL;
 static bool hcidump_fallback = false;
@@ -1416,6 +1417,55 @@ int control_tty(const char *path, unsigned int speed)
 	return 0;
 }
 
+static void rtt_callback(int id, void *user_data)
+{
+	struct control_data *data = user_data;
+	ssize_t len;
+
+	do {
+		len = jlink_rtt_read(data->buf + data->offset,
+					sizeof(data->buf) - data->offset);
+		data->offset += len;
+		process_data(data);
+	} while (len > 0);
+
+	if (mainloop_modify_timeout(id, 1) < 0)
+		mainloop_exit_failure();
+}
+
+int control_rtt(char *jlink, char *rtt)
+{
+	struct control_data *data;
+
+	if (jlink_init() < 0) {
+		fprintf(stderr, "Failed to initialize J-Link library\n");
+		return -EIO;
+	}
+
+	if (jlink_connect(jlink) < 0) {
+		fprintf(stderr, "Failed to connect to target device\n");
+		return -ENODEV;
+	}
+
+	if (jlink_start_rtt(rtt) < 0) {
+		fprintf(stderr, "Failed to initialize RTT\n");
+		return -ENODEV;
+	}
+
+	printf("--- RTT opened ---\n");
+
+	data = new0(struct control_data, 1);
+	data->channel = HCI_CHANNEL_MONITOR;
+	data->fd = -1;
+
+	if (mainloop_add_timeout(1, rtt_callback, data, free_data) < 0) {
+		free(data);
+		return -EIO;
+	}
+
+	return 0;
+}
+
 bool control_writer(const char *path)
 {
 	btsnoop_file = btsnoop_create(path, 0, 0, BTSNOOP_FORMAT_MONITOR);