Specifications

Programming the VMEbus Interface
5
5
5-11
When using the EPC-8 this way to perform VMEbus accesses, you would typically set
up the E-page window for interrupt acknowledge accesses. Also note that the direct
access mappings do not cover the entire VMEbus A32 address range and do not pro-
vide all VMEbus-defined address modifier encodings, but you can use the
E-page mechanism if needed to provide these.
Generating IACKs in Protected Mode
As noted in the description of protected mode direct VMEbus accesses, the values of
address bits 24 and 25 determine the access mode. Setting bit 26 will cause an IACK
(if the high-order address nibble is 1, C, or D, i.e., only in A16 direct access mode).
Note that an IACK will override any of the other access modes.
With the EPC-8 programmers are not restricted to using the E-page in order to signal
an IACK; direct VME memory access is possible. In protected mode you cannot
access physical addresses -- only virtual addresses. Thus for addressing, map the flat
32-bit physical address to a virtual pointer.
To acknowledge a VME interrupt and acquire its 16-bit status/id:
Multiply the VME interrupt number by two and add the result to
0xC4000000.
Map the resulting physical address 0xC4000000 to a protected mode
address.
Read the 16-bit status/id value from the resulting virtual mode address.
Whether or not a protected mode environment uses virtual memory is an attribute of
the operating system, not of being in protected mode. There are protected mode
environments that do not use virtual memory (like most DOS extenders).
Programming the Watchdog Timer
The watchdog timer on the EPC-8 can be set to either halt the system or reboot when a
watchdog timer event occurs. The counter will cause a watchdog event after a
specified time.
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