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*******
Printer
*******
Role: device only. The Printer class provides bulk OUT data from a host print
spooler, optional bulk IN data for a bidirectional printer, and standard device
ID, port-status, and soft-reset requests.
Configuration
=============
Enable ``CFG_TUD_PRINTER`` and define the RX/TX FIFO and endpoint sizes. Add a
``TUD_PRINTER_DESCRIPTOR``; protocol 2 is the bidirectional interface used by
the TinyUSB example.
.. code-block:: c
#define CFG_TUD_PRINTER 1
#define CFG_TUD_PRINTER_RX_BUFSIZE 64
#define CFG_TUD_PRINTER_TX_BUFSIZE 64
#define CFG_TUD_PRINTER_RX_EPSIZE 64
#define CFG_TUD_PRINTER_TX_EPSIZE 64
.. list-table::
:header-rows: 1
:widths: 42 17 41
* - Option
- Default
- What it controls
* - ``CFG_TUD_PRINTER_RX_BUFSIZE`` /
``CFG_TUD_PRINTER_TX_BUFSIZE``
- Required when enabled
- Software FIFO capacity per printer interface. TX is still allocated
even if the application normally only receives print data.
* - ``CFG_TUD_PRINTER_RX_EPSIZE`` /
``CFG_TUD_PRINTER_TX_EPSIZE``
- Device bulk maximum
- Endpoint transfer buffer and descriptor packet size in each direction.
Data received from the host is available through
``tud_printer_read_available()`` and ``tud_printer_read()``. Send status or
bidirectional data with ``tud_printer_write()`` and flush when the response
should leave promptly. Use the ``tud_printer_n_*`` forms for multiple
interfaces.
.. list-table::
:header-rows: 1
:widths: 42 58
* - Data API or callback
- What it does
* - ``tud_printer_n_read_available()`` /
``tud_printer_n_read()``
- Reports and removes bytes sent by the print spooler.
* - ``tud_printer_n_write_available()`` /
``tud_printer_n_write()``
- Reports TX room and copies as much bidirectional response data as fits.
* - ``tud_printer_n_write_flush()``
- Starts a short TX transfer and returns the number of bytes submitted.
* - ``tud_printer_n_read_flush()`` /
``tud_printer_n_write_clear()``
- Discards pending receive or transmit FIFO data, for example on soft
reset.
* - ``tud_printer_rx_cb()`` /
``tud_printer_tx_complete_cb()``
- Announces new input or newly available TX capacity.
Control callbacks
=================
``tud_printer_get_device_id_cb()`` must return an IEEE 1284 device ID. Its
first two bytes are the big-endian total length, including those two bytes, and
the buffer must remain valid through transfer completion. A typical text body
is ``MFG:Vendor;MDL:Model;CMD:PCL;CLS:PRINTER;``.
Return current online, error, and paper state from
``tud_printer_get_port_status_cb()`` using
``tusb_printer_port_status_t``. In ``tud_printer_soft_reset_cb()``, cancel the
current print job and reset the class-facing parser without resetting unrelated
parts of a composite device.
``tud_printer_request_complete_cb()`` marks the end of the control transfer and
is the safe point to reuse request-specific application state, including a
dynamically selected device-ID buffer.
See :doc:`../../examples/device/printer_to_cdc` for bidirectional data and all
three class requests.
Specification used: *USB Device Class Definition for Printing Devices*,
Version 1.1.
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