Gamma™ : Version 6.4
	QNX 4

`dev_read`

dev_read — is a modification of QNX 4 dev_read.

Syntax

dev_read (devno, nchars, min_chars, time, timeout)

Arguments

devno: A device id number returned from dev_open.
nchars: The number of characters to read.
min_chars: The minimum number of characters to read.
time: The inter-character time limit.
timeout: A timeout value for the entire read.

Returns

A buffer containing the characters which were successfully returned from this call, or nil if an error occurred.

Description

This function is a modification of the QNX 4 dev_read function. It is currently only available in QNX 4.

This function does not support the proxy and armed arguments to the C dev_read function. The characters read from the device are returned in a buffer rather than filled in to a buf argument as with the C function. Otherwise, the function of this call is identical to the QNX 4 dev_read function.

The min, time, and timeout values are used as follows:

Table 16. dev_read min, time, and timeout values

min	time	timeout	Description
0	0	0	Returns immediately with as many bytes as are currently available (up to nchars bytes).
M	0	0	Return with up to nchars bytes only when at least M bytes are available.
0	T	0	Return with up to nchars bytes when at least one byte is available, or T * 0.1 sec has expired.
M	T	0	Return with up to nchars bytes when either M bytes are available or at least one bytes has been received and the inter-byte time between any subsequently received characters exceeds T * 0.1 sec.
0	0	t	Reserved.
M	0	t	Return with up to nchars bytes when t * 0.1 sec has expired, or M bytes are available.
0	T	t	Reserved.
M	T	t	Return with up to nchars when M bytes are available, or t * 0.1 sec has expired and no characters are received, or at least one byte has been received and the inter-byte time between any subsequently received characters exceeds T * 0.1 sec.
0	T	t	Reserved.
M	T	t	Return with up to nchars when M bytes are available, or t * 0.1 sec has expired and no characters are received, or at least one byte has been received and the inter-byte time between any subsequently received characters exceeds T * 0.1 sec.

If an error occurs the errno is set. The following error constants are relevant:

EAGAIN The O_NONBLOCK flag is set on the devno.

EBADF The devno argument is invalid or not open for read

EINTR The function was interrupted by a signal

EIO The process cannot read data from the devno

ENOSYS This function is not supported for the given devno

Example

Gamma> id = dev_open("/dev/ser1",O_RDWR);	
4
Gamma> x = dev_read(id,5,1,0,100);
#[104 101 108 108 111]
Gamma> buffer_to_string(x);
"hello"


QNX 4		dev_setup

dev_read