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, which always emits a bidirectional (protocol 2) interface with both bulk endpoints.

#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

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 size in each direction. Each must be at least the _epsize packet size passed to TUD_PRINTER_DESCRIPTOR.

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.

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 Printer to CDC for bidirectional data and all three class requests.

Specification used: USB Device Class Definition for Printing Devices, Version 1.1.