ieee1284_get_deviceid — retrieve an IEEE 1284 Device ID
#include <ieee1284.h>
ssize_t
ieee1284_get_deviceid( | port, | |
| daisy, | ||
| flags, | ||
| buffer, | ||
len); |
struct parport * | port; |
int | daisy; |
int | flags; |
char * | buffer; |
size_t | len; |
This function is for retrieving the IEEE 1284 Device ID
of the specified device. The device is specified by the
port to which it is attached, and
optionally an address (daisy) on the
daisy chain of devices on that port.
daisy should be −1 to
indicate that the device is not participating in a IEEE
1284.3 daisy chain, meaning it is the last (or only) device
on the port, or should be a number from 0 to 3 inclusive to
indicate that it has the specified daisy chain address (0 is
next to the port).
The flags parameter should be a
bitwise union of any flags that the program wants to use.
Available flags are:
F1284_FRESHGuarantee a fresh Device ID. A cached or OS-provided ID will not be used.
The provided buffer must be at
least len bytes long, and will contain
the Device ID including the initial two-byte length field and
a terminating zero byte on successful return, or as much of
the above as will fit into the buffer.
A return value less than zero indicates an error as
below. Otherwise, the return value is the number of bytes of
buffer that have been filled. A
return value equal to the length of the buffer indicates that
the Device ID may be longer than the buffer will
allow.
The device did not provide an IEEE 1284 Device ID
when interrogated (perhaps by the operating system if
F1284_FRESH was not
specified).
One or more of the supplied flags is not supported in this implementation, or if no flags were supplied then this function is not implemented for this type of port or this type of system. This can also be returned if a daisy chain address is specified but daisy chain Device IDs are not yet supported.
F1284_FRESH was specified
and the library is unable to access the port to
interrogate the device.
There is not enough memory.
There was a problem initializing the port.
The port parameter is
invalid.
Unless the F1284_FRESH flag is
given, the library will try to find the device's ID as
unobtrusively as possible. First it will ask the operating
system if it knows it, and then it will try actually asking
the device for it. Because of this, the Device ID may be
partially computed (the length field, for example) or even
partially missing if the operating system has only remembered
some parts of the ID. To guarantee that you are getting the
bytes that the device sent, use
F1284_FRESH. Be aware that the
operating system may allow any user to inspect the Device IDs
that it provides, whereas device access is normally more
restricted.
The initial two-byte length field is a big-endian 16 bit unsigned integer provided by the device and may not be accurate. In particular, it is meant to indicate the length of the entire string including the length field itself; however, some manufacturers exclude the length field or just set the length field to some arbitrary number greater than the ID length.