Size Is 2K - IBM System/370 145 Manual

CCW1
CCW2
CAW at location 72
CCW1
CCW2
CCW List Provided by the F'rogram
0
I/O area
address
I/O area
address
8
j
31
Virtual storage
address
1
0
33
R
E
48 63
CCW List and IDAl's Constructed for the 1/0 Operation
o
8
New translated CCW list
used for Start I/O
IDAL1
address
IDAL2
address
,
o
31 33
Rea I storage
address
IDA
flag
37
3625
IDAW1
0
IDAW2
0
IDAW3
0
0
IDAW1
o
IDAW2 0
o
IDAL1
Rea I storage
address I/O area
Real storage
address I/O area
Real storage
address I/O area
8 31
IDAL2
Rea I storage
address I/O area
Real storage
address I/O area
8
31
CCW1 I/O area in real
storage - 3625 bytes
2048
bytes
Page frame Y
Page frame Z
CCW2 I/O area in real
storage - 3625 bytes
Page frame B
Figure 15.10.4. Example of IDAL's ]~equired for a CCW list when page
size is 2K
The channel detects a 2K boundary by monitoring I/O area address bits
21-31. When these bits change from all ones to all zeros. the first
byte of the next 2K real storage block is indicated. At this point. the
channel accesses the second IDAW in the list to obtain the next real
storage I/O area address to be used, and the data transfer operation
continues. (In the Model 1q:5. IDAW's are prefetched.) The channel
continues using the IDAL until the operation indicated by the CCW
completes (CCW count reaches zero, IRG on tape is reached. etc.) The
next CCW is accessed if command or dlata chaining is indicated. Bit 31
is inspected and the I/O operation continues as described until the CCW
list is exhausted.
When a program operates in paged mode. the CCW list for an I/O
operation must be inspected. the ne~r
ccw
list with translated addresses
must be built. and the appropriate IDAL's must be constructed prior to
issuing a START I/O instruction. At the completion of an I/O operation,
A Guide to the IBM System/310 Model 145
71