Device control register
Encyclopedia
A device control register (DCR) is a register
that resides in an element of a System-on-a-chip
(e.g. a memory
unit, a DMA controller, other bus controller
, a timer
etc.) and allows to configure, control and probe this element.
Typically, a microprocessor
or a processor core is the entity that initiates these tasks, thus a master-slave configuration is created. Communications between the master (the processor) and the slaves (other on-chip elements or peripheral devices) are carried out using a specialized bus with its own address space
and means of access.
Because DCRs exist architecturally and physically outside the main processor core, their semantics
is independent of the processor functions. Thus they are not specified by the processor programming manuals, which typically define the DCR space, but make no claims regarding which facility or device corresponds to which part of the space.
DCRs are typically accessed through the use of privileged instructions.
Examples:
Processor register
In computer architecture, a processor register is a small amount of storage available as part of a CPU or other digital processor. Such registers are addressed by mechanisms other than main memory and can be accessed more quickly...
that resides in an element of a System-on-a-chip
System-on-a-chip
A system on a chip or system on chip is an integrated circuit that integrates all components of a computer or other electronic system into a single chip. It may contain digital, analog, mixed-signal, and often radio-frequency functions—all on a single chip substrate...
(e.g. a memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
unit, a DMA controller, other bus controller
Controller (computing)
In computing and especially in computer hardware, controller is a chip, an expansion card, or a stand-alone device that interfaces with a peripheral device...
, a timer
Timer
A timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. Whereas a stopwatch counts upwards from zero for measuring elapsed time, a timer counts down from a specified time interval, like an hourglass.Timers can be mechanical, electromechanical,...
etc.) and allows to configure, control and probe this element.
Typically, a microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
or a processor core is the entity that initiates these tasks, thus a master-slave configuration is created. Communications between the master (the processor) and the slaves (other on-chip elements or peripheral devices) are carried out using a specialized bus with its own address space
Address space
In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity.- Overview :...
and means of access.
Because DCRs exist architecturally and physically outside the main processor core, their semantics
Semantics
Semantics is the study of meaning. It focuses on the relation between signifiers, such as words, phrases, signs and symbols, and what they stand for, their denotata....
is independent of the processor functions. Thus they are not specified by the processor programming manuals, which typically define the DCR space, but make no claims regarding which facility or device corresponds to which part of the space.
DCRs are typically accessed through the use of privileged instructions.
Examples:
- The embedded PowerPCPowerPCPowerPC is a RISC architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM...
chips have a special DCR Bus which allows the processor to access other devices on the bus, bypassing standard memory and bus controllers. The data transfers to DCRs are initiated using the special mtdcr (move to DCR) and mfdcr (move from DCR) instructions. - The compute cores of Blue GeneBlue GeneBlue Gene is a computer architecture project to produce several supercomputers, designed to reach operating speeds in the PFLOPS range, and currently reaching sustained speeds of nearly 500 TFLOPS . It is a cooperative project among IBM Blue Gene is a computer architecture project to produce...
supercomputer expose DCRs for access to JTAGJTAGJoint Test Action Group is the common name for what was later standardized as the IEEE 1149.1 Standard Test Access Port and Boundary-Scan Architecture. It was initially devised for testing printed circuit boards using boundary scan and is still widely used for this application.Today JTAG is also...
functions .