[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
In message <370A0DC4.C42B4BFA@paradigm-inc.com>, email@example.com write
>This seems like a dumb question, but has anyone had experience with any
>PCI cards which try to master to themselves?
I've heard rumours that some of the NCR/Symbios SCSI chips do this.
>I appear to have a SCSI
>host adapter which trys to do this. I haven't found anything in the
>specs which would preclude such operation (perhaps as a self-test?).
The NCR chips have a MOVE MEMORY instruction, which moves some number
of bytes from source to destination.
Due to hardware limitations (no indirect addressing mode (this which means
copying a register to the address field of a direct-addressing instruction,
which could reside in the on-chip RAM of later parts (early parts executed
code from main memory) and byte at a time access to internal registers (the
original parts could take a few hundred microseconds for each instruction,
so a single move-memory instruction was substantially faster than the eight
(SFBR must be either source or destination for a register operation) register
operations)), MOVE MEMORY instructions see some use during normal operation
of the chip.
Not special-casing addresses in the chip's address spaces would
simplify implementation of MOVE MEMORY instruction, and such bus
accesses could be par for the course.
<a href="http://www.poohsticks.org/drew/">Home Page</a>
For those who do, no explanation is necessary.
For those who don't, no explanation is possible.