UCOM(9)

UCOM(9) | Kernel Developer's Manual | UCOM(9)

# NAME

ucom — interface for USB tty like devices

# DESCRIPTION

The ucom driver is a (relatively) easy way to make a USB device look like a tty(4). It basically takes two bulk pipes, input and output, and makes a tty out of them. This is useful for a number of device types, e.g., serial ports (see uftdi(4)), modems (see umodem(4)), and devices that traditionally look like a tty (see uvisor(4)).

Communication between the real driver and the ucom driver is via the attachment arguments (when attached) and via the ucom_methods struct

# ATTACHMENT

    struct ucom_attach_args {
    	int portno;
    	int bulkin;
    	int bulkout;
    	u_int ibufsize;
    	u_int ibufsizepad;
    	u_int obufsize;
    	u_int obufsizepad;
    	usbd_device_handle device;
    	usbd_interface_handle iface;
    	struct ucom_methods *methods;
    	void *arg;
    };

int portno
  identifies the port if the devices should have more than one ucom attached. Use the value UCOM_UNK_PORTNO if there is only one port.
int bulkin
  the number of the bulk input pipe.
int bulkout
  the number of the bulk output pipe.
u_int ibufsize
  the size of the read requests on the bulk in pipe.
u_int ibufsizepad
  the size of the input buffer. This is usually the same as ibufsize.
u_int obufsize
  the size of the write requests on the bulk out pipe.
u_int ibufsizepad
  the size of the output buffer. This is usually the same as obufsize.
usbd_device_handle device
  a handle to the device.
usbd_interface_handle iface
  a handle to the interface that should be used.
struct ucom_methods *methods
  a pointer to the methods that the ucom driver should use for further communication with the driver.
void *arg
  the value that should be passed as first argument to each method.

# METHODS

The ucom_methods struct contains a number of function pointers used by the ucom driver at various stages. If the device is not interested in being called at a particular point it should just use a NULL pointer and the ucom driver will use a sensible default.

    struct ucom_methods {
    	void (*ucom_get_status)(void *sc, int portno,
    				u_char *lsr, u_char *msr);
    	void (*ucom_set)(void *sc, int portno, int reg, int onoff);
    #define UCOM_SET_DTR 1
    #define UCOM_SET_RTS 2
    #define UCOM_SET_BREAK 3
    	int (*ucom_param)(void *sc, int portno, struct termios *);
    	int (*ucom_ioctl)(void *sc, int portno, u_long cmd,
    			  void *data, int flag, struct lwp *l);
    	int (*ucom_open)(void *sc, int portno);
    	void (*ucom_close)(void *sc, int portno);
    	void (*ucom_read)(void *sc, int portno, u_char **ptr,
    			  uint32_t *count);
    	void (*ucom_write)(void *sc, int portno, u_char *to,
    			   u_char *from, uint32_t *count);
    };

void (*ucom_get_status)(void *sc, int portno, u_char *lsr, u_char *msr)
  get the status of port portno. The status consists of the line status, lsr, and the modem status msr. The contents of these two bytes is exactly as for a 16550 UART.
void (*ucom_set)(void *sc, int portno, int reg, int onoff)
  Set (or unset) a particular feature of a port.
int (*ucom_param)(void *sc, int portno, struct termios *t)
  Set the speed, number of data bit, stop bits, and parity of a port according to the termios(4) struct.
int (*ucom_ioctl)(void *sc, int portno, u_long cmd, void *data, int flag, struct lwp *l)
  implements any non-standard ioctl(2) that a device needs.
int (*ucom_open)(void *sc, int portno)
  called just before the ucom driver opens the bulk pipes for the port.
void (*ucom_close)(void *sc, int portno)
  called just after the ucom driver closes the bulk pipes for the port.
void (*ucom_read)(void *sc, int portno, u_char **ptr, uint32_t *count)
  if the data delivered on the bulk pipe is not just the raw input characters this routine needs to increment ptr by as many characters to skip from the start of the raw input and decrement count by as many characters to truncate from the end of the raw input.
void (*ucom_write)(void *sc, int portno, u_char *dst, u_char *src, uint32_t *count)
  if the data written to the bulk pipe is not just the raw characters then this routine needs to copy count raw characters from src into the buffer at dst and do the appropriate padding. The count should be updated to the new size. The buffer at src is at most ibufsize bytes and the buffer at dst is ibufsizepad bytes.

Apart from these methods there is a function

void ucom_status_change(struct ucom_softc *)

which should be called by the driver whenever it notices a status change.

# SEE ALSO

tty(4), uftdi(4), umodem(4), usb(4), uvisor(4)

# HISTORY

This ucom interface first appeared in NetBSD 1.5.

July 9, 2012 | NetBSD 7.1