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---------------------------
Beaglebone Cape-Manager
---------------------------
The beaglebone cape manager driver allows the automatic use of external
peripheral capes to be automatically supported by Linux without any manual
setup required by the user.
Each beaglebone cape should contain an EEPROM that describes
it in a fixed I2C address on the i2c2 bus of the baseboard.
The format of the EEPROM is defined in the beaglebone reference
manual at:
http://beagleboard.org/static/beaglebone/latest/Docs/Hardware/BONE_SRM.pdf
Reading the part number and revision information the manager
requests a firmware file formatted as a device tree overlay blob.
Applying the overlay the devices are instantiated and the cape is
ready to be used.
For instance if the part-number is BB-BONE-SERL-03 and the version is 00A1
the firmware file requested will be BB-BONE-SERL-03-00A1-00A1.dtbo
It will be located by the in-kernel firmware
loader in the usual place, i.e. /lib/firmware/`uname -r`, /lib/firmware etc.
The driver supports the following parameters (either as part of the kernel
command line or supplied at module insertion time).
disable_partno: A comma delimited list of PART-NUMBER[:REV] of
disabled capes.
enable_partno: A comma delimited list of PART-NUMBER[:REV[:PRIO]] of
enabled capes.
boot_scan_period: The boot scan period in ms. When the cape manager is built-in
the kernel image, the firmware loader cannot find the files
before the rootfs is mounted. This parameter controls the
period with which the boot state is checked in that case.
There's a sysfs control interface which is defined at the ABI documentation
area.
Theory of operation:
--------------------
On driver probe the I2C EEPROM of the baseboard is read and information about
the current baseboard is retrieved. This information includes the mapping from
baseboard board name to DT friendly compatible string. I.e. the "A335BONE" board
name from EEPROM is mapped to the "ti,beaglebone" compatible string which should
be present in the dtbo to be loaded.
Afterwards the EEPROMs declared in each slot are probed, and the EEPROMs found
are decoded keeping track the cape part-number and version data.
Using the part-number and version a firmware file is requested (the firmware
file requested is <part-number>-<version>.dtbo).
The dtbo is unflattend and the resulting device tree is matched against a
compatible baseboard, and in case of multiple parallel loading capes the
priorities defined are honored. That means that when there are multiple capes
being loaded in parallel the ones with the lowest priority number are loaded
first.
Applying the device tree overlay makes the cape operational, as if it was part
of the kernel's booting device tree.
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