T-Kernel Specification (1.B0.02)

5.3. DEVICE MANAGEMENT FUNCTIONS 231
The time required for read start processing differs with the device; return of control is not necessarily
immediate.
In the case of device-specific data, the start and size units are decided for each device. With
attribute data, start is an attribute data number and size is in bytes. The attribute data of the
data number designated in start is read. Normally size must be at least as large as the size of
the attribute data to be read. Reading of multiple attribute data in one operation is not possible.
When size = 0 is designated, actual reading does not take place but the current size of data that
can be read is checked.
Whether or not a new request can be accepted while a read or write operation is in progress
depends on the device driver. If a new request cannot be accepted, the request is queued. The
timeout for request waiting is set in tmout. The TMO POL or TMO FEVR attribute can be designated
for tmout. Note that what times out is request acceptance. Once a request has been accepted,
this function does not time out.
E ID
E OACV
E LIMIT
E TMOUT
E ABORT
Other
dd is invalid or not open
Open mode is invalid (read not permitted)
Number of requests exceeds the limit
Busy processing other requests
Processing aborted
Errors returned by device driver
• ER tk_srea_dev( ID dd, INT start, VP buf, INT size, INT *asize )
Synchronous read. This is equivalent to the following.
ER tk_srea_dev( ID dd, INT start, VP buf, INT size, INT *asize )
{
ER er, ioer;
er = tk_rea_dev(dd, start, buf, size, TMO_FEVR);
if ( er > 0 ) {
er = tk_wai_dev(dd, er, asize, &ioer, TMO_FEVR);
if ( er > 0 ) er = ioerr;
}
return er;
}
• ID tk_wri_dev( ID dd, INT start, VP buf, INT size, TMO tmout )
dd
start
buf
size
tmout
return code
Device descriptor
write start location (≥ 0: Device-specific data, < 0: Attribute data)
Buffer holding data to be written
Size of data to be written
Request acceptance timeout (ms)
Request ID or error
Starts writing device-specific data or attribute data to a device. This function starts writing only,
returning to its caller without waiting for the write operation to finish. The space designated
in buf must be retained until the write operation completes. Write completion is waited for by
tk wai dev.
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T-Kernel 1.B0.02