Drivers, Descriptors and the "OEM global area"

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Ralf Kiefer

Nov 7, 2018, 9:32:40 PM11/7/18

actually I want to understand the different areas of RAM which are used
by SCF drivers and devices. I cannot find the informations which I need
in my Technical I/O Manual (for 3.0) or Peter Dibble's Insights 3.0 :-(

My SCF driver is the sc68681: one driver, two devices in each chip,
several chips. I must exchange some data (2 bytes) between the devices
from each chip. There are two possible solutions: the driver creates a
data module the first time it's iniz'd. This is like an overkill ;-)
The second solution seems to be using the "OEM global area" (so called
by Peter Dibble).

Is there a description for these details?

My idea actually: the Devcon field from the descriptor stores the offset
from that area called "OEM global area". The description of that area is
collected in the "systype.d" file individually for each machine.

That's my problem:
MVME335, two M68681 and four descriptors: /t1 .. /t4. t1 and t2 use the
first chip and share their shadow registers in the first 2 bytes of the
devcon area. t3 and t4 share their shadow registers in the second 2
bytes. If there is another device driver which needs some bytes to store
it will use the following 252 bytes (or less). Correct?

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