Multi-tasking register set mapping system which changes a register set

Abstract

An I/O processor includes an execution unit (EU), a register file, an I/O bus sequencer and a local bus sequencer. The EU decodes an ACCESS instruction having a pointer to a parameter register comprised of: a number of fields for storing a sequencer code identifying one of the sequencers; a logical byte specifying a location in memory to be addressed and valid and block bits; a reply register set pointer to a register set in the register file designated to receive a reply to the ACCESS instruction; and, a length field specifying the location and length of a data block in the register file from which data is to be obtained. A data pointer is generated by taking the logical byte in the parameter register and passing it through a register set mapper to produce a register file physical address. The valid bit of the logical byte is turned off as it is translated by the register the mapper so that the bus sequencer can take control over the corresponding register set. The block bit is set upon the condition that the ACCESS instruction attempts to access a register set whose valid bit is not set, and the block bit is reset upon the condition that the task which is executing the ACCESS instruction attempts to access a register set whose block and valid bits are set.