trying to understand rationale of unix stream i/o concept Post: 302334764

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Top Forums UNIX for Dummies Questions & Answers trying to understand rationale of unix stream i/o concept Post 302334764 by Perderabo on Thursday 16th of July 2009 11:23:54 AM

07-16-2009

Administrator Emeritus

A method is like a subroutine. An example might be a file of dictionary words. Instead of writing. you "insert" the word. Somehow the system keeps the words in alphabetical order. You can retrieve a list of all word in alphabetical order or you can search for a word. But the data file itself is a black box and you can't access it. If you put 1,234 bytes worth of words into the data file it will be bigger than 1,234 bytes. The system needs some extra stuff to find it's way around the file. This extra stuff is the control blocks.

And believe it or not, there used to be a sequential file which behaved like a really stupid tape drive. You could read it. You could even read it byte-by-byte. But after you read, say, byte number 123, you had two choices: read byte 124 or close the file. However, the OS could predict a program's behavior rather easily and this was fast (for it's day).

There might be a "random" file where you could seek and then read, but it was slow. After seeking to byte 123 and reading one byte, you could next seek to byte 124 and read that. But if you wanted a sequential file, you were supposed use a sequential file, not a random file.

Mind you, a single data file might be opened as "sequential" by one program and "random" by another. But then each program had a different interface (or subroutine or method) to read the file. However there was no way to execute a data file or to read a program file.

There were many file types and OS's competed by offering more file types. The Unix model of just one file type displaced all of this.

Perderabo

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i2cget

I2CGET(8)						      System Manager's Manual							 I2CGET(8)

NAME

       i2cget - read from I2C/SMBus chip registers

SYNOPSIS

       i2cget [-f] [-y] i2cbus chip-address [data-address [mode]]
       i2cget -V

DESCRIPTION

       i2cget is a small helper program to read registers visible through the I2C bus (or SMBus).

OPTIONS

       -V     Display the version and exit.

       -f     Force  access to the device even if it is already busy. By default, i2cget will refuse to access a device which is already under the
	      control of a kernel driver. Using this flag is dangerous, it can seriously confuse the kernel driver in question. It can also  cause
	      i2cget to return an invalid value. So use at your own risk and only if you know what you're doing.

       -y     Disable  interactive  mode. By default, i2cget will wait for a confirmation from the user before messing with the I2C bus. When this
	      flag is used, it will perform the operation directly. This is mainly meant to be used in scripts. Use with caution.

       There are two required options to i2cget. i2cbus indicates the number or name of the I2C bus to be scanned.  This number should	correspond
       to one of the busses listed by i2cdetect -l. chip-address specifies the address of the chip on that bus, and is an integer between 0x03 and
       0x77.

       data-address specifies the address on that chip to read from, and is an integer between 0x00 and 0xFF. If  omitted,  the  currently  active
       register will be read (if that makes sense for the considered chip).

       The mode parameter, if specified, is one of the letters b, w or c, corresponding to a read byte data, a read word data or a write byte/read
       byte transaction, respectively. A p can also be appended to the mode parameter to enable PEC. If the  mode  parameter  is  omitted,  i2cget
       defaults  to a read byte data transaction, unless data-address is also omitted, in which case the default (and only valid) transaction is a
       single read byte.

WARNING

       i2cget can be extremely dangerous if used improperly. I2C and SMBus are designed in such a way that an SMBus read transaction can  be  seen
       as  a  write  transaction  by  certain chips. This is particularly true if setting mode to cp (write byte/read byte with PEC). Be extremely
       careful using this program.

SEE ALSO

       i2cdump(8), i2cset(8)

AUTHOR

       Jean Delvare

       This manual page was strongly inspired from those written by David Z Maze for i2cset.

								     May 2008								 I2CGET(8)