Input/Output Streams¶
lbuild module: modm:io
The modm::IOStream class contains efficient formatting that supports both
C++ std::basic_ostream-like formatting via operator << as well as
implementing printf via the modm:printf module.
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);
AVR supported features
All expensive features including printf are disabled by default to reduce
firmware size! Please check the options.
modm::endl does NOT implicitly flush!
Flushing is extremely expensive on embedded systems, therefore modm::endl
does not implicitly flush the stream. Please call modm::flush explicitly.
Redirecting IOStreams¶
The modm::IODeviceWrapper transforms any peripheral device that provides static
write() and read() functions into an IODevice:
// configure a UART
using Uart = Uart0;
// wrap it into an IODevice
modm::IODeviceWrapper<Uart, modm::IOBuffer::BlockIfFull> 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!";
IODevice Buffer Behavior¶
The modm::IODeviceWrapper can be configured to discard or block in case the
device is full. Discarding data is always non-blocking, however, blocking on
write involves waiting in a loop until the device has space. This can cause a
deadlock when called inside an interrupt!
If compiled with the modm:processing:fiber module, the blocking behavior
allows the fiber to yield while waiting for the device. To prevent interlaced
output from different fibers, the write(char) function is protected by a
mutex that releases when a newline character \n is written. The flush()
function is also mutex protected to allow one fiber to reliably flush the
stream without having other fibers push data into the device.
Options¶
with_float¶
Support for floating point formatting
On AVRs floating point values can be printed, however, the formatting cannot be specified and all values are printed as scientific-notation exponential floating point
Default: no avr
Default: yes hosted, rp, sam, stm32
Inputs: [yes, no]
with_long_long¶
Support for 64-bit integer formatting
Default: no avr
Default: yes hosted, rp, sam, stm32
Inputs: [yes, no]
Input Dependency: yes -> modm:printf
with_printf¶
Support for printf-style formatting
Default: no avr
Default: yes hosted, rp, sam, stm32
Inputs: [yes, no]
Input Dependency: yes -> modm:printf