RadiSys EPC-26A/27, Manual

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Theory of Operation
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Video Controllers
The EPC can operate with or without a video controller such as the EXM-13A.
At power-up, the BIOS searches the EXM configuration information by slot number
(starting at 0) for the first video EXM where the card enable bit is set. If one is
found, it will be initialized and used at power-up and the search exits.
If no video card is enabled in the EXM configuration information, a second search is
done across the EXM expansion interface (beginning at slot 0) looking for an EXM
video adapter. When a video adapter is found, the system will enable it and quit the
search.
If no video controller is present, the BIOS operates without one. Programs that use
the standard operating system and BIOS character output functions run successfully
because the output is ignored. However, programs that rely on specific video modes,
that write directly into the video RAM, or that directly call video BIOS functions,
will fail.
Front Panel LED
The EPC-26A/27 has one green LED on the front panel. This RUN LED is lit
whenever the EPC's DRAM memory is being accessed. It first comes on at power-up
and should remain lit as long as the system is running. It is normal for the RUN LED
to flicker during power-up. If the processor halts (or hangs) or runs entirely out of
cache, the LED will go out.
Optional Flash/SRAM Memory
An option exists to purchase the EPC-26A/27 with a combination of 128 KBytes of
SRAM and 2 or 4 MBytes of flash memory included on the EPC. RadiSys also
markets an EXM-2A expansion module with even more flexibility in combining flash
and SRAM. Note that the Flash/SRAM included with the EPC is compatible with the
EXM-2A architecture. If this option is included, the EPC appears to software as
though there were an integrated EXM-2A in the system.