compata@cup.portal.com (08/02/88)
I wish to add an IO board to my Xenix system. The only way to address this board is via dual-ported memory. The precise addresses are switch-selectable on the board. The board does not generate any interrupts although it is possible to cause an interrupt to the board by writing to an output port. I understand that /dev/mem would allow access to all of physical memory. However, I don't know what physical memory is not already in use. More importantly, I can't be sure that the same physical memory will always be available. I would like to find a way to address this board in a portable way, so the same technique could be later used on SysV, and possibly on non-Intel processor machines. Any suggestions will be very welcome. Email gratefully accepted. Dave Close, Compata, Arlington, Texas - compata@cup.portal.com
jeffh@hpubvwa.HP.COM (Jeff Harrell) (08/06/88)
Memory-mapped I/O is best implemented on the Motorola chips. INTEL didn't even get that right! -- DISCLAMER: It's true!! I think... Jeff (Spectra Software) Harrell (206) 927-9268
jbayer@ispi.UUCP (id for use with uunet/usenet) (08/07/88)
In article <11650007@hpubvwa.HP.COM>, jeffh@hpubvwa.HP.COM (Jeff Harrell) writes: > Memory-mapped I/O is best implemented on the Motorola chips. INTEL > didn't even get that right! > Wrong, wrong, wrong. This statement shows that you do not know what memory- mapped I/O is. This reminds me of an old debate I read in some computer magazine back in the dark ages when people were still putting computer kits together. I saw the discussion when somebody boasted that their SWTP 6800 (South West Technical Products) had memory mapped I/O and the IMSI 8080 did not. The same ignorance applies. Memory mapped I/O is any I/O which accesses memory addresses instead of using special instructions to access the device. Taken to the extreme even access to normal memory can be considered to be memory mapped I/O. ANY COMPUTER WHICH ACCESSES MEMORY CAN HAVE MEMORY MAPPED I/O. Possibly Intel didn't get some- thing right, but it wasn't memory-mapped I/O. Jonathan Bayer Intelligent Software Products, Inc. 19 Virginia Ave. Rockville Centre, NY 11570 uunet!ispi!jbayer
jeffh@weycord.WEYCO.COM (08/12/88)
Johnathan Bayer writes: > Possibly Intell didn't get something right, but it wasn't memory- > mapped I/O. Touche'. All I/O is memory mapped in the in the MC680xx processors. (but, to say accessing memory is memory-mapped I/O is pure bunk!) Jeff (Spectra-Software) Harrell hpubvwa!weycord!jeffh