c58da9fbc3
IMPORTANT: this change has a docs/UPDATING entry! This rename is unfortunately necessary because NetBSD has decided to create its own service(8) utility, and we will want to import theirs as well. The two can obviously not coexist. Also move ours from /bin to /sbin, as it is a superuser-only utility. Change-Id: Ic6e46ffb3a84b4747d2fdcb0d74e62dbea065039
65 lines
2.2 KiB
Plaintext
65 lines
2.2 KiB
Plaintext
Minix i2c Driver
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================
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TODO: this probably belongs on the wiki
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Overview
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--------
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This is the driver for the i2c bus. It provides the same /dev interface as
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NetBSD and OpenBSD (see dev/i2c/i2c_io.h). It also provides an interface for
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other drivers to access the I2C bus using Minix IPC.
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Organization and Layout
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-----------------------
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i2c.c generic i2c bus driver
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arch/ arch specific code
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earm/ earm specific code
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omap_i2c.c AM335X/DM37XX i2c bus driver
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omap_i2c.h AM335X/DM37XX function prototypes
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omap_i2c_registers.h AM335X/DM37XX register offsets, etc.
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Testing the Code
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----------------
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Below are the steps needed to start up the i2c driver instances. Though,
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now they get started at boot in /usr/etc/rc, it's still useful to know if
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you take down the service and need to start it again.
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Creating the device files (this is already done automatically, but if not):
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cd /dev && MAKEDEV i2c-1 && MAKEDEV i2c-2 && MAKEDEV i2c-3
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Starting up the instances:
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/sbin/minix-service up /service/i2c -dev /dev/i2c-1 -label i2c.1 -args instance=1
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/sbin/minix-service up /service/i2c -dev /dev/i2c-2 -label i2c.2 -args instance=2
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/sbin/minix-service up /service/i2c -dev /dev/i2c-3 -label i2c.3 -args instance=3
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There is an i2cscan program from NetBSD which can detect devices on the bus:
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i2cscan -r /dev/i2c-1
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i2cscan -r /dev/i2c-2
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i2cscan -r /dev/i2c-3
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Limitations
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-----------
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The i2c controllers used in the am335x and the dm37xx do not support zero
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byte transfers. Writing 0 bytes is a common method used to probe the bus
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for devices. Most of the address ranges i2cscan scans are done by this
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method. Therefore, only a subset of devices on the bus will be detected by
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i2cscan (i.e. the devices it detects using the 1 byte read method). See
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the register description for I2C_CNT in the technical reference manuals
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for details about why 0 byte transfers are not allowed.
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Developing I2C Device Drivers
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-----------------------------
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The driver for the EEPROM (a.k.a. drivers/cat24c256) is the hello world of
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Minix i2c device drivers. It shows how to use the i2cdriver library and
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how to use the bus for reads and writes. commands/eepromread is another
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place to look if you're interested in accessing devices through the /dev
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interface.
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