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White Rabbit Switch - Software
Commit 0f64a06f authored by Alessandro Rubini's avatar Alessandro Rubini
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doc: added an overview of the hal 

Signed-off-by: Alessandro Rubini's avatarAlessandro Rubini <rubini@gnudd.com>
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doc/wrs-developer-manual.in
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......@@ -1819,6 +1819,35 @@ for details about how they are used:
@end table
@c ##########################################################################
@node The HAL Process
@chapter The HAL Process
In the initial days of White Rabbit Switch, developers tried to have
everything managed by a single ``Hardware Abstraction Layer'' process,
the HAL. The process still exists but its role is smaller than it
used to, so some of the code is likely unused. After release 4.1
we started a serious audit of the @sc{hal}.
The implementation is currently split between @i{userspace/wrsw_hal}
and @i{userspace/libwr}. Some of the @i{libwr} functions are
used by other processes, but some are just librarized parts of
the @sc{hal} process (again, we are not very clean and tidy).
If you run @t{ps} in the switch, you'll see there are two @sc{hal}
process, one being a child of the other. The child is forked by the
@i{mini-rpc} library, to poll shared memory (the communication channel
with the @i{rt} subsystem). @i{mini-rpc} has one file descriptor per
channel, so users can run @i{select()} or @i{poll()}, thus this trick
to be able to turn a shared-memory channel into a file descriptor.
This is documented in @i{mini-rpc} documentation. The polling time is
currently 25ms.
The @sc{hal} process is in charge of replying to IPC requests
(@i{hal_exports.c}), driving the fan speed according to temperature
(@i{libwr/fan.c}) and monitoring ports (this is spread in several
files related to @i{i2c} communication).
@c ##########################################################################
@node Reboot/Reset Diagnostics
@chapter Reboot/Reset Diagnostics
......
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