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David van Moolenbroek 597151d963 libchardriver: full API rewrite 
The new API now covers the entire character driver protocol, while
hiding all the message details. It should therefore be used by all
new character drivers. All existing drivers that already made use of
libchardriver have been changed to use the new API.

As one of the most important API changes, support for scatter and
gather transfers has been removed, as several key drivers already
did not support this, and it could be supported at the safecopy
level instead (for a future readv/writev).

Additional changes include:

- respond to block device open requests to avoid hanging VFS threads;
- add support for sef_cancel.

Change-Id: I1bab6c1cb66916c71b87aeb1db54a9bdf171fe6b
2014-03-01 09:04:50 +01:00
..
arch/earm arm:replace ifdef's by runtime checks in the i2c driver. 2013-12-17 11:32:38 +01:00
i2c.c libchardriver: full API rewrite 2014-03-01 09:04:50 +01:00
Makefile kernel: add padconf kernel call 2013-08-28 12:53:05 -04:00
README.txt i2c: initial bus drivers for am335x and dm37xx 2013-07-15 11:11:13 -04:00

README.txt 

Minix i2c Driver
================

TODO: this probably belongs on the wiki

Overview
--------

This is the driver for the i2c bus. It provides the same /dev interface as
NetBSD and OpenBSD (see dev/i2c/i2c_io.h). It also provides an interface for
other drivers to access the I2C bus using Minix IPC.

Organization and Layout
-----------------------

i2c.c					generic i2c bus driver
arch/					arch specific code
	earm/				earm specific code
		omap_i2c.c		AM335X/DM37XX i2c bus driver	
		omap_i2c.h		AM335X/DM37XX function prototypes
		omap_i2c_registers.h 	AM335X/DM37XX register offsets, etc.

Testing the Code
----------------

Below are the steps needed to start up the i2c driver instances. Though,
now they get started at boot in /usr/etc/rc, it's still useful to know if
you take down the service and need to start it again.

Creating the device files (this is already done automatically, but if not):

cd /dev && MAKEDEV i2c-1 && MAKEDEV i2c-2 && MAKEDEV i2c-3

Starting up the instances:

/bin/service up /usr/sbin/i2c -dev /dev/i2c-1 -label i2c.1 -args instance=1
/bin/service up /usr/sbin/i2c -dev /dev/i2c-2 -label i2c.2 -args instance=2
/bin/service up /usr/sbin/i2c -dev /dev/i2c-3 -label i2c.3 -args instance=3

There is an i2cscan program from NetBSD which can detect devices on the bus:

i2cscan -r /dev/i2c-1
i2cscan -r /dev/i2c-2
i2cscan -r /dev/i2c-3

Limitations
-----------

The i2c controllers used in the am335x and the dm37xx do not support zero
byte transfers. Writing 0 bytes is a common method used to probe the bus
for devices. Most of the address ranges i2cscan scans are done by this
method. Therefore, only a subset of devices on the bus will be detected by
i2cscan (i.e. the devices it detects using the 1 byte read method). See
the register description for I2C_CNT in the technical reference manuals
for details about why 0 byte transfers are not allowed.

Developing I2C Device Drivers
-----------------------------

The driver for the EEPROM (a.k.a. drivers/cat24c256) is the hello world of
Minix i2c device drivers. It shows how to use the i2cdriver library and
how to use the bus for reads and writes. commands/eepromread is another
place to look if you're interested in accessing devices through the /dev
interface.