HP-UX Reference (11i v1 00/12) - 3 Library Functions A-M (vol 6)

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blmode(3C) blmode(3C)

(TO BE OBSOLETED)

NAME

blopen(), blclose(), blread(), blget(), blset() - terminal block-mode library interface

SYNOPSIS

#include <sys/blmodeio.h>

int blopen(int fildes);

int blclose(int bfdes);

int blread(int bfdes, char *buf, size_t nbyte);

int blget(int bfdes, struct blmodeio *arg);

int blset(int bfdes, const struct blmodeio *arg);

DESCRIPTION

This terminal library interface allows support of block-mode transfers with HP terminals. Block mode only

affects input processing. Therefore, data is written with the standard write() interface (see write(2)).

In character mode, the terminal sends each character to the system as it is typed. However, in block mode,

data is buffered and possibly edited locally in the terminal memory as it is typed, then sent as a block of

data when the [Enter] key is pressed on the terminal. During block-mode data transmissions, the incom-

ing data is not echoed by the interface and no special character processing is performed, other than recog-

nizing a data block terminator character. For subsequent character mode transmissions, the existing ter-

mio state (see termio(7)) continues to determine echo and character processing.

Block-mode protocol has two component parts: block-mode handshake and block-mode transmission.

Block-Mode Handshake

At the beginning of a read, a trigger character is sent to the terminal to notify it that the system wants a

block of data (the trigger character, if deﬁned, is sent at the beginning of all reads, whether in character- or

block-mode. It is necessary for block-mode reads to work correctly).

After receiving the trigger character, and when the user has typed all the data into the terminal’s memory

and pressed the [Enter] key, the terminal sends an alert character to the system to notify it that the ter-

minal has a block of data to send.

The system might then send user-deﬁnable cursor-positioning or other data sequences to the terminal, such

as for cursor-home or lock-keyboard.

The system then sends a second trigger character to the terminal. In response, the terminal transmits the

data block as described in the Block-Mode Transmission section.

Block-Mode Transmission

The second part of the block-mode protocol is the block-mode transmission. After the block-mode

handshake has successfully completed, the terminal transmits the data block to the system. During this

transmission of data, the incoming data is not echoed by the system and no special character processing is

performed, other than recognizing the data block termination character. It is possible to bypass the block-

mode handshake and have the block-mode transmission occur after only the ﬁrst trigger character is sent,

see CB_BMTRANS below.

It is possible to intermix both character-mode and block-mode data transmissions. If

CB_BMTRANS (see

below) is set, all transfers are block-mode transfers. When

CB_BMTRANS is not set, character mode

transmissions are processed as described in termio(7). In this case, if an alert character is received any-

where in the input data, the transmission mode is automatically switched to block mode for a single

transmission. Any data received before the alert is discarded. The alert character can be escaped with a

backslash (

\) character.

XON/XOFF Flow Control

To prevent data loss, XON/XOFF ﬂow control should be used between the system and the terminal. The

IXOFF bit (see termio(7)) should be set and the terminal strapped appropriately. If ﬂow control is not used,

it is possible for incoming data to overﬂow and be lost. (Note: some older terminals do not support

XON/XOFF ﬂow control.)

Read Requests

Read requests that receive data from block-mode transmissions do not return until the transmission is com-

plete (the terminal has transmitted all characters). If the read is satisﬁed by byte count or if a data

Section 3−−42 − 1 − HP-UX Release 11i: December 2000

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