Cray CRAY-1 - Page 175

I
I/O interrupts can be caused by the following:
• On all output channels, if (CA) becomes equal to (CL), then
for each
of the module types on the transmission of the last
four parcels:
OK module - Resume for last parcel sets interrupt
DO module - Resume for last word sets interrupt
SI module - Interrupt sets when last Ready is sent.
I (CA) becomes equal to (CL) on DV input module.
I External device disconnect received on any input channel.
I Channel error condition (described later in this section).
The number of the channel causing an interrupt can be determined by the
use of a
033 instruction which reads to Ai the highest priority channel
number requesting an interrupt. The lowest numbered channel has the high-
est priority. The interrupt request continues until cleared by the monitor
program at which time an interrupt from the next highest priority channel,
if present, may be sensed.
INPUT CHANNEL PROGRAMMING
To start an input operation, the CRAY-l program must perform the following
steps:
1.
Set the channel limit address to the last word address+l (LWA+l).
See figure 6-1.
2.
Set the channel current address to the first word address (FWA).
Setting the current address causes the channel active flag to be set and
the channel is then ready to receive data. When a 4-parcel word is
assembled, the word is stored in memory at the address contained in the
channel
current address register. When the word is accepted by memory,
the current address is advanced by 1.
The external transmitting device sends a disconnect pulse to indicate
the end of the transfer. When the disconnect is received, the channel
interrupt flag sets and a test is performed to check for a partially
2240004
6-3
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