18 Aug
2015
18 Aug
'15
9:30 a.m.
On 2015-08-18 14:46, Paul Koning wrote:
To put things another way. Think of BR level as "interrupt priority". A
bit coarse, since position on the bus further refined interrupt priority
within a BR level. (Closer to the CPU -> higher priority than farther
On Aug 17, 2015, at 10:48 PM, Jay Jaeger
<cube1 at charter.net> wrote:
BR level is the bus request level for an Interrupt. BR 4 is typical.
On Unibus machines, more of the BR levels were used. The rule of thumb was BR4 for slow
devices (like terminals and printers), BR5 for fast devices (disks and tapes), BR6 for
real time critical devices (clock, also DECtape because you had to respond to a ?read
block number? interrupt fast enough to start reading the block before it passed over the
heads). BR7 could in theory be used by devices but I don?t believe it ever was in
practice. from the CPU, for devices on the same BR level.)
And then the CPU could choose to block all interrupts at a specific BR
level and lower.
Johnny