
IBM2520L8767
IBM Processor for ATM Resources
atmrm.chapt04.01
08/27/99
ATM Virtual Memory Logic (VIMEM)
Page 161 of 553
09
When set, this bit indicates that the virtual memory logic has detected a read operation that caused a page fault. This is an
invalid condition because the data required for a read operation should have been previously initialized by a write operation,
so no page fault should ever occur on a read operation. If the corresponding bit in the lock register is reset, a page will be
mapped into the current virtual buffer segment and the data that previously was written in that page will be returned. This bit
can come on in several situations that are not really errors. In these cases, the associated interrupt and lock bits can be reset
so that this error does not cause the adapter to halt normal operation. Several of these conditions are: When predictive fill is
enabled, a read from the end of a buffer may cause a predictive read that crosses a virtual segment boundary and causes
this bit to be set. If a small buffer (fits entirely in the cache) is copied from one IBM2520L8767 buffer to another
IBM2520L8767 buffer, a subsequent read of the last bytes written will cause this bit to be set if the cache hasn’t been flushed
between the write and the read, and the last write cycle did not write all 4 bytes, and the address that is being written/read is
within the first 0x20 bytes of a virtual segment.
08
When set, this bit indicates that the virtual memory logic has detected an access of a virtual buffer that falls above the limit
set by the buffer maximum size register.
07
When set, this bit indicates that the virtual memory logic has detected an access that does not fall in one of the currently
mapped buffer segments based upon the currently-configured virtual buffer map size.
06
When set, this bit indicates that a virtual access has been detected that used a base register that had an invalid associated
buffer size configured in the low order bits.
05
When set, this bit indicates that a virtual access has been detected that used a base register that was not on the correct
memory boundary. For example, if a base register is set up to use 2-KB buffers, then the base register must be set up on a
2-KB boundary.
04
When set, this bit indicates that a virtual access has been detected that used a base register that contained a value of 0.
03
Reserved.
02
When set, this bit indicates that the virtual memory logic has detected a memory access that resulted in the generation of a
buffer index that was greater than the currently configured maximum derived from the VIMEM virtual memory total bytes reg-
ister.
01
When set, this bit indicates that the currently configured size of buffers is invalid.
00
When set, this bit indicates that the map base register contains an invalid value. Two possible causes are that bits 5-2 are
not zero or bits 31-6 are zero.
Bit(s)
Description