1. xerox 560 computer system - The UK Mirror Service

4. Each unit-record controller (internal or external)requires one I/O subchannel per each unit record deviceattached, up to a maximum of eight.5. The maximum number of internal device controllerswithin an MIOP is eight (where a unit-record devicecontroller is equivalent to one, regardless of thenumber of assigned subchannels).6. Any I/O subchannel not assigned to an internal devicecontroller may be assigned to an external device controller.Thus, if an MIOP has no internal device controller,all 16 I/O subchannels may be assigned toexternal device controllers.ROTATING MEMORY PROCESSOR (RMP)Each RMP is a speci_al purpose, single-channel lOP designedto enhance high-speed data transfers between main memoryand anyone of up to eight disk units. Functionally, anRMP is comparable to an MIOP, except: (1) at any giventime, only one disk unit may be selected for a data transferoperation, . (2) data transfer rate of disk units are generallyhigher than data transfer rates of I/O devices attached toan MIOP, and (3) the device controller function is performedby the RMP, hence disk units are connected directlyto the RMP rather than via a device controller. (Note:Although only one disk unit may be actively transferdngdata at any given time, the other units may be active inperforming control functions, e. g., seeking).2. Depending upon various programming considerations,the command list may be contained within one or moreareas of memory and each area may be comprised ofone or more I/O command doublewords (IOCDs).3. Command list continuity between 10CDs relating to thesame logical record or to the same logical file may bespecified (see "Data Chain Flag" and "Command ChainFlag ll under II Operationa I 10CDs"). Command listcontinuity between portions of a command list locatedin different areas of main memory may be accomplishedby including a control 10CD within the command list(see "Transfer in Channel II under "Control 10CDs").4. Each 10CD is comprised of two words in contiguousmemory word locations. The first word must be storedin an even memory word location and the second wordmust be stored in the next consecutive (odd) memoryword location. Each IOCD is either an operationalIOCD or a control IOCD and contains coded parametersto define either a complete I/Ooperation or an integralportion of an I/Ooperation. (See "Operational IOCD"and IIControl IOCD" for further detai Is. )OPERATIONAL lOCOAn operational IOCD may contain up to five fields ofparameters, as required, to define either an entire I/o operationor an integral portion of an I/o operation._ Thegeneral format and description of parameters containedwithin an operational 10CD are as follows:iNPUT jOUTPUT PKOCESSOR liOfij FUNUAMENTAlSThis section contains general information, programming concepts,and definition of terms pertaining to I/O operationsperformed by Input/Output Processors (i. e., MIOP andRMP systems). The large variety of I/O devices which maybe used with these lOPs precludes a detailed or exhaustivedescription of features which are unique to each device.Likewise, a general reference "Refer to an appropriateXerox peripheral reference manual" is made rather thanciting specific manuals.Within this manual, the following terminology is used todifferentiate the hierarchy of control during an I/o operation:The BP executes instructions, the lOPs execute commands,and the device controller/device execute orders.COMMAND LISTEach I/O operation performed by an lOP must be definedby a command list. The characteristics and requirements ofa command list are as follows:1. It is normally created by a BP-executed programprior to the time that the defined I/o operation isinitiated. It must reside in main memory when the I/ooperation is initiated and subsequently executed.ORDERThis 8-bit field (bit positions 0-7), if required, may becoded to specify either an input or an output order that isexecuted by the device controller/device. General codingformats and functions of typical I/o orders are listed below:Bit Positiono 1 2 3 4 5 6 7 Order FunctionMMMMMM01MMMMMM10MMMMMM11MMMMOMMMM10000WriteReadControlSenseReadBackwardOutput operationInput operationOutput controlinformationInput control informationInput data, in reversesequenceRotating Memory Processor (RMP)/Input/Output Processor (lOP) Fundamentals 143