PC IO fig IO 0 Remember from PC

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PC IO fig IO. 0 Remember from PC IO==> The System Bus ( a logical construct) PCI bus. …Backbone. . most like System bus IDE Disk controller bus- 2 disks per IDE bus (master and Slave) SCSI Controller and bus Expansion Bus Parallel Port (e. g. parallel printer cable), Serial port (USB bus), Keyboard (make/break) contacts Graphics Controller and Monitor Video/Graphics card and Memory 1

IO_Variations - Control Unit and Buffer A Read = Dev -> Buffer -> Memory A Write = Memory -> Buffer -> Dev - 2 IO Interrupts per IO - Match device speed to Bus speed Minimize Buffer utilization - Direct Memory Access (DMA) – off-load data move from CPU 2

IO_Variations - Mainframe (fig IO. 1 360 IO) Many System Buses …now called “Channels” Multiple Control Units on each Channel Almost all Control Units (CU’s) are buffered… not originally- but speed mismatch became a problem Byte-Multiplexor, Selector, and then Block-Multiplexor Control Unit can connect to multiple Channels (fig IO. 2) Control unit can connect to different channels on different CPUs Channel to Channel connections possible if close Channel Programs allow many complex operations without an IO Interrupt (covered later) 3

Mainframe IO Basic Addressing Structure SIO instruction Specifies “device address” Device address defines path to device Today IO subsystem determines “path” to device Minimizes bottlenecks to device Supports higher availability in case of failures (Channels, CUs. ) Provides image of “floating” channels Cost- longer time to initiate an IO TPF doesn’t use it Some IO Instructions (e. g. SIOF) release processor “early” 4

Mainframe IO Notion of a sub-channel i. e. uuu a. k. a. UCW Contains information about an IO operation to a device e. g. CCW address, current state Contains current path to device from processor 5

Mainframe IO - CCW Format 0 (64 bits. . 8 bytes) – (fig IO. 4) Command Code, Data address(24 bits), Flags, spare, Byte Count Flags CD – data chain CC – command chain SLI – suppress length indication (e. g. read a terminal line) SKIP – skip data transfer PCI - program control interrupt IDA - data address points to first IDAW word (fig IO. 5) MIDA -data address points to first MIDAW 6

Mainframe IO -CCW Format 1 (64 bits. . 8 bytes) (fig IO 6 a) Command Code, Flags, Byte Count, Data address(31 bits) Flags CD – data chain CC – command chain SLI – suppress length indication (e. g. read a terminal line) SKIP – skip data transfer PCI - program control interrupt IDA - data address points to first IDAW word (fig IO. 5) SUSPEND – suspend program. . before this command MIDA -data address points to first MIDAW (fig IO. 6 a, b) 7

Mainframe IO IDAW and MIDAW formats IDAW 1 - 0|| 31 bit address IDAW 2 - 64 bit address MIDAW – first 5 byres reserved flags bytecount 64 bit address Flags Last MIDAW in program Skip Data Transfer interrupt 8

Mainframe IO -A 9

Mainframe IO -A 1

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