[HECnet] Which is THE dec printer?

[Johnny Billquist]

On 2014-01-15 15:42, Cory Smelosky wrote:
On Wed, 15 Jan 2014, Dave McGuire wrote:

On 01/15/2014 06:35 PM, Cory Smelosky wrote:
A lot of people (myself included) insisted on direct-in-the-bus
printer controllers when we saw how badly serial printers tanked the
system when we connected them to DZ11s. ;)

Oh I can imagine that.   A dedicated controller would have MUCH higher
bandwidth than the <1.5mbitcapable on the DZ11. ;)

It's the interrupt load that's the problem.   It could TANK an 11/750.


Didn't the DZ11 depend on the CPU for interrupts?

Eh... Every controller depends on the CPU for interrupts. That's what interrupts mean.
However, the problem with the DZ11 is that it generates interrupts for each character sent as well as each character received. It do have some smart in it, so you can get a few characters per interrupt under some circumstances, but the interface basically just killed a machine when you did lots of I/O, because of the interrupt load.

Isn't that why say...the DHV11 had processors to offload serial
processing to?

DH11, DHV11 and DHU11 all use DMA for output, meaning you only get one interrupt when the output is done. Which is *way* better.

	Johnny