1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
|
.. highlight:: cpp
.. _lang-serialusb:
``SerialUSB``
=============
Used for communication between the Maple board and a computer.
.. contents:: Contents
:local:
Introduction
------------
In addition to three :ref:`serial ports <lang-serial>`, the Maple's
STM32 microprocessor includes a dedicated USB peripheral. This
peripheral is used to emulate a regular serial port for use as a
terminal. The emulated terminal is relatively slow; it is best for
transferring data at regular serial speeds (kilobaud).
Library access to the emulated serial port is provided through the
``SerialUSB`` object. You can mostly use ``SerialUSB`` as a drop-in
replacement for ``Serial1``, ``Serial2``, and ``Serial3``.
.. warning:: The ``SerialUSB`` functionality includes a 50 millisecond
timeout for writes, and does not try to detect if the USB host is
"really" connected, or just enumerated and initialized.
This means that if you have a number of calls to one of the
``SerialUSB`` ``write()`` or ``print()`` functions in your code,
and you are not monitoring ``SerialUSB`` on a computer, your
program will run much slower than if it is being monitored or
totally disconnected (run off of a battery).
You can avoid this behavior by :ref:`deciphering the port status
using the DTR and RTS line status <lang-serialusb-safe-print>` (the
behavior of these control lines is platform dependent and we no
longer interpret them by default).
Library Documentation
---------------------
The ``SerialUSB`` object is an instance of the ``USBSerial`` class,
which is documented in this section. This means that you can use any
of these functions by writing
``SerialUSB.functionName(arguments...)``. For example, to print the
message "hello, world!", you can write ``USBSerial.println("hello,
world!")``.
.. cpp:class:: USBSerial
Emulated serial-over-USB class. ``SerialUSB`` is the predefined
(singleton) instance.
.. _lang-serialusb-begin:
.. cpp:function:: USBSerial::begin()
Set up the USB peripheral for emulated serial communication. The
peripheral is configured this way by default; calling this function
should only be necessary if you have disabled the peripheral using
``SerialUSB.end()``.
.. _lang-serialusb-end:
.. cpp:function:: USBSerial::end()
Disables the USB peripheral. Note that using this function will
terminate all USB communications between the Maple and the USB
host; in particular, it implies that you won't be able to upload
any new programs without resetting the board or using
:ref:`perpetual bootloader mode
<troubleshooting-perpetual-bootloader>`.
.. cpp:function:: unsigned int USBSerial::available()
Returns the number of bytes available for reading.
.. _lang-serialusb-read:
.. cpp:function:: unsigned char USBSerial::read()
Returns the next available, unread character. If there are no
available characters (you can check this with :cpp:func:`available
<USBSerial::available>`), the call will block until one
becomes available.
.. cpp:function:: USBSerial::print(unsigned char b)
Print the given byte over the USB connection.
.. cpp:function:: USBSerial::print(char c)
Print the given character over the USB connection. 7-bit clean characters
are typically interpreted as ASCII text.
.. cpp:function:: USBSerial::print(const char *str)
Print the given null-terminated string over the USB connection.
.. cpp:function:: USBSerial::print(int n)
Print the argument's digits over the USB connection, in decimal format.
Negative values will be prefixed with a ``'-'`` character.
.. cpp:function:: USBSerial::print(unsigned int n)
Print the argument's digits over the USB connection, in decimal format.
.. cpp:function:: USBSerial::print(long n)
Print the argument's digits over the USB connection, in decimal
format. Negative values will be prefixed with a ``'-'`` character.
.. cpp:function:: USBSerial::print(unsigned long n)
Print the argument's digits over the USB connection, in decimal
format.
.. cpp:function:: USBSerial::print(long n, int base)
Print the digits of ``n`` over the USB connection, in base ``base``
(which may be between 2 and 16). The ``base`` value 2 corresponds
to binary, 8 to octal, 10 to decimal, and 16 to hexadecimal.
Negative values will be prefixed with a ``'-'`` character.
.. cpp:function:: USBSerial::print(double n)
Print ``n``, accurate to 2 digits after the decimal point.
.. _lang-serialusb-println:
.. cpp:function:: USBSerial::println(char c)
Like ``print(c)``, followed by ``"\r\n"``.
.. cpp:function:: USBSerial::println(const char *c)
Like ``print(c)``, followed by ``"\r\n"``.
.. cpp:function:: USBSerial::println(unsigned char b)
Like ``print(b)``, followed by ``"\r\n"``.
.. cpp:function:: USBSerial::println(int n)
Like ``print(n)``, followed by ``"\r\n"``.
.. cpp:function:: USBSerial::println(unsigned int n)
Like ``print(n)``, followed by ``"\r\n"``.
.. cpp:function:: USBSerial::println(long n)
Like ``print(n)``, followed by ``"\r\n"``.
.. cpp:function:: USBSerial::println(unsigned long n)
Like ``print(n)``, followed by ``"\r\n"``.
.. cpp:function:: USBSerial::println(long n, int base)
Like ``print(n, b)``, followed by ``"\r\n"``.
.. cpp:function:: USBSerial::println(double n)
Like ``print(n)``, followed by ``"\r\n"``.
.. cpp:function:: USBSerial::println()
Prints ``"\r\n"`` over the USB connection.
.. cpp:function:: USBSerial::write(unsigned char ch)
Sends one character over the USB connection. This function is
currently blocking, although nonblocking writes are a planned
future extension.
This is a low-level function. One of the ``print()`` or
``println()`` functions is likely to be more useful when printing
multiple characters, when formatting numbers for printing, etc.
.. cpp:function:: USBSerial::write(const char* str)
Send the given null-terminated character string over the USB
connection.
This is a low-level function. One of the ``print()`` or
``println()`` functions is likely to be more useful when printing
multiple characters, when formatting numbers for printing, etc.
.. cpp:function:: USBSerial::write(void *buf, unsigned int size)
Writes the first ``size`` bytes of ``buf`` over the USB connection.
Each byte is transmitted as an individual character.
This is a low-level function. One of the ``print()`` or
``println()`` functions is likely to be more useful when printing
multiple characters, when formatting numbers for printing, etc.
Examples
--------
.. _lang-serialusb-safe-print:
**Safe print**: This function should run smoothly and not block; the
LED should blink at roughly the same speed whether being monitored,
running from battery, or connected but not monitored. You may need to
experiment with the DTR/RTS logic for your platform and device
configuration. ::
#define LED_PIN BOARD_LED_PIN
void setup() {
/* Set up the LED to blink */
pinMode(LED_PIN, OUTPUT);
}
void loop() {
// LED will stay off if we are disconnected, and will blink
// quickly if USB is unplugged (battery power, etc.).
if(SerialUSB.isConnected()) {
digitalWrite(LED_PIN, 1);
}
delay(100);
// If this logic fails to detect if bytes are going to be read
// by the USB host, then the println() take a long time,
// causing a very slow LED blink. If the characters are
// printed and read, the blink will only slow a small amount
// when "really" connected, and will be fast fast when the
// virtual port is only configured.
if(SerialUSB.isConnected() && (SerialUSB.getDTR() || SerialUSB.getRTS())) {
for(int i = 0; i < 10; i++) {
SerialUSB.println(123456, BIN);
}
}
digitalWrite(LED_PIN, 0);
delay(100);
}
|
