Linux provides a informal hardware abstraction layer, otherwise RTLinux would be
impossible -- and Linux itself would be painful to port.
That is, Linux makes use of calls to "cli" and "sti" etc. which RTLinux converts into
calls
to the emulator code.
To be honest, I've never understand what Paolo means by the concept of a hardware
abstraction
layer beyond some renaming and use of indirect pointers to implement the redirection.
In V2
RTLinux uses a technique in which Linux "cli" is redefined to be a static call to a
rtl
function, in V3 x86 uses a indirect jump. In later versions, we will get rid of this
jump
again -- it was easy to implement but it does have a cost that is more noticeable in
lower
end processors. So from my point of view: cli compiles to "jsr rtl_cli" or
cli compiles to "movl rtl_table,%eax; movl CLIOFFSET(%eax),%eax; jsr *%eax" is
conceptually
the same with only a performance/ease_of_programming tradeoff.
On Mon, Jun 19, 2000 at 08:40:27AM -0700, roux jean-denis wrote:
> Hi guys,
>
> I would like to know how RTLinux works. I know that
> both RTAI and RTL turn Linux to a task running when no
> real-time activity occurs and that RTAI use the
> concept of the Hardware Abstraction Layer (RT HAL) but
> not RTL. That's why I would like to know what concept
> use RTLinux.
>
> Jean-Denis ROUX
>
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