These module docs are in beta and may be incomplete.
modm Input/Output Streams¶
modm::IOStream class contains efficient formatting that supports both
std::basic_ostream-like formatting via
operator << as well as
implementing a reasonably large subset of
modm::IOStream stream(device); stream << "format number 8: " << uint8_t(8) << " or as signed -100: " << int8_t(-100); stream << modm::endl; stream.printf("format number 8: %u or as signed -100: %d", 8, -100);
The format string is composed of zero or more directives: ordinary characters (not %), which are copied unchanged to the output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments. Each conversion specification is introduced by the % character. The arguments must properly correspond (after type promotion) with the conversion specifier. After the %, the following appear in sequence:
Zero or more of the following flags:
-A negative field width flag; the converted value is to be left adjusted on the field boundary. The converted value is padded on the right with blanks, rather than on the left with blanks.
' '(space) A blank should be left before a positive number produced by a signed conversion (d).
+A sign must always be placed before a number produced by a signed conversion. A
+overrides a space if both are used.
- An optional decimal digit string specifying a minimum field width. If the converted value has fewer characters than the field width, it will be padded with spaces on the left (or right, if the left-adjustment flag has been given) to fill out the field width.
- An optional
lllength modifier, that specifies that the argument for the
xconversion is a 8-bit ("h"), 32-bit ("l") or 64-bit ("ll") rather than 16-bit.
The conversion specifiers and their meanings are:
c: char (8-bit)
s: string (
p: pointer (
d: signed decimal
u: unsigned decimal
Combined with the length modifiers you get:
d: signed 16-bit
ld: signed 32-bit
lld: signed 64-bit (not yet)
u: unsigned 16-bit
lu: unsigned 32-bit
llu: unsigned 64-bit (not yet)
hx: 8-bit hex
x: 16-bit hex
lx: 32-bit hex
llx: 64-bit hex (not yet)
-100 as argument in the right type:
%c: %s: %p: 0x0100 %d: -100 %ld: -100 %u: 65436 %lu: %hx: 0x9c %x: 0xff9c %lx: 0xffffff9c
s: The "char *" argument is expected to be a pointer to an array of character type (pointer to a string). Characters from the array are written up to (but not including) a terminating NULL character; if a precision is specified, no more than the number specified are written. If a precision is given, no null character need be present; if the precision is not specified, or is greater than the size of the array, the array must contain a terminating NULL character.
%is written. No argument is converted. The complete conversion specification is
In no case does a non-existent or small field width cause truncation of a numeric field; if the result of a conversion is wider than the field width, the field is expanded to contain the conversion result.
modm::IODeviceWrapper transforms any peripheral device that provides static
read() functions into an
You have to decide what happens when the device buffer is full and you cannot write to it at the moment. There are two options:
- busy wait until the buffer is free, or
- discard the bytes that cannot be written.
Option 1 has the advantage, that none of your data will be lost, however, busy-waiting can take a long time and can mess up your program timings. There is also a high risk of deadlock, when writing to a IODevice inside of an interrupt and then busy-waiting forever because the IODevice requires interrupts itself to send out the data.
It is therefore highly recommended to use option 2, where surplus data will be discarded. You should increase the IODevice buffer size, if you experience missing data from your connection. This behavior is also deadlock safe when called from inside another interrupt, and your program timing is minimally affected (essentially only coping data into the buffer).
There is no default template argument, so that you hopefully make a conscious decision and be aware of this behavior.
// configure a UART using Uart = Uart0; // wrap it into an IODevice modm::IODeviceWrapper<Uart, modm::IOBuffer::DiscardIfFull> device; // use this device to print a message device.write("Hello"); // or create a IOStream and use the stream to print something modm::IOStream stream(device); stream << " World!";
// Class class modm::IODevice; class modm::IODeviceWrapper< class Device, IOBuffer behavior >; class modm::IOStream; // Function IOStream& modm::ascii(IOStream &ios); IOStream& modm::bin(IOStream &ios); IOStream& modm::black(IOStream &ios); IOStream& modm::blue(IOStream &ios); IOStream& modm::cyan(IOStream &ios); IOStream& modm::endl(IOStream &ios); IOStream& modm::flush(IOStream &ios); IOStream& modm::green(IOStream &ios); IOStream& modm::hex(IOStream &ios); IOStream& modm::magenta(IOStream &ios); IOStream& modm::red(IOStream &ios); IOStream& modm::white(IOStream &ios); IOStream& modm::yellow(IOStream &ios); // Enum enum IOBuffer;