597151d963
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 |
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arch/earm | ||
i2c.c | ||
Makefile | ||
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.