chris@mimsy.UUCP (Chris Torek) (01/13/89)
In article <6936@june.cs.washington.edu> ka@june.cs.washington.edu (Kenneth Almquist) writes: >... on some machines, devices can only do I/O to contiguous regions >of physical memory. ... The Tahoe has some devices that act like this. The `solution' used in 4.3BSD is to have a few hundred kbytes of physically contiguous memory allocated to the vba (Versabus/VMEbus adapter) code, and to copy the data in and out. Gross, but it works; the vba allocation code is careful to figure out whether this sort of munging is really necessary. I had to do something similar in the BI KDB driver, which reads through hardware PTEs; it needs physically contiguous PTEs even in user space, and they are not available. (Fortunately, >80% of the transfers done in the system run through the buffer cache.) -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163) Domain: chris@mimsy.umd.edu Path: uunet!mimsy!chris