Data processing circuits and interfaces

• US 20020161988A1
• Filed: 10/29/2001
• Published: 10/31/2002
• Est. Priority Date: 09/23/1994
• Status: Active Grant

• Current Assignee: Cambridge Solutions Limited (DXC Technology Company)
• Original Assignee: Cambridge Solutions Limited (DXC Technology Company)
• Inventors: Barlow, Stephen John, Collier, James Digby, Morfey, Alistair Guy
• Granted Patent: US 6,901,503 B2
• Time in Patent Office: Days
• US Class Current: 712/221
• CPC Class Codes: G06F 1/3203 Power management, i.e. event-based initiation of a power-saving mode
• CPC Class Codes: G06F 1/3237 by disabling clock generation or distribution
• CPC Class Codes: G06F 11/2236 to test CPU or processors
• CPC Class Codes: G06F 11/3648 using additional hardware
• CPC Class Codes: G06F 11/3656 using a specific debug interface
• CPC Class Codes: G06F 15/7832 on one IC chip (single chip microprocessors)
• CPC Class Codes: G06F 7/57 Arithmetic logic units [ALU], i.e. arrangements or devices for performing two or more of the operations covered by groups G06F7/483 – G06F7/556 or for performing logical operations G06F7/49, G06F7/491 take precedence
• CPC Class Codes: G06F 9/30 Arrangements for executing machine instructions, e.g. instruction decode for executing microinstructions G06F9/22
• CPC Class Codes: G06F 9/30014 with variable precision
• CPC Class Codes: G06F 9/30032 Movement instructions, e.g. MOVE, SHIFT, ROTATE, SHUFFLE
• CPC Class Codes: G06F 9/3005 to perform operations for flow control
• CPC Class Codes: G06F 9/30083 Power or thermal control instructions
• CPC Class Codes: G06F 9/30101 Special purpose registers
• CPC Class Codes: G06F 9/30145 Instruction analysis, e.g. decoding, instruction word fields
• CPC Class Codes: G06F 9/3016 Decoding the operand specifier, e.g. specifier format
• CPC Class Codes: G06F 9/30167 of immediate specifier, e.g. constants
• CPC Class Codes: G06F 9/322 for non-sequential address
• CPC Class Codes: G06F 9/323 for indirect branch instructions
• CPC Class Codes: G06F 9/324 using program counter relative addressing
• CPC Class Codes: G06F 9/3869 Implementation aspects, e.g. pipeline latches; pipeline synchronisation and clocking
• CPC Class Codes: Y02D 10/00 : Energy efficient computing, e.g. low power processors, power management or thermal management
• CPC Class Codes: Y02D 30/50 : in wire-line communication networks, e.g. low power modes or reduced link rate

Abstract

An integrated circuit contains a microprocessor core, program memory and separate data storage, together with analog and digital signal processing circuitry. The ALU is 16 bits wide, but a 32-bit shift unit is provided, using a pair of 16-bit registers. The processor has a fixed length instruction format, with an instruction set including multiply and divide operations which use the shift unit over several cycles. No interrupts are provided. external pins of the integrated circuit allow for single stepping and other debug operations, and a serial interface (SIF) which allows external communication of test dat or working data as necessary. The serial interface has four wires (SERIN, SEROUT, SERCLK, SERLOADB), allowing handshaking with a master apparatus, and allowing direct access to the memory space of the processor core, without specific program control. Within each processor cycle, the processor circuitry is divided into plural stages, and latches are interposed between the stages to minimize power consumption.

Claims

1. A processor embedded with other circuitry as part of an application specific integrated circuit, the processor comprising:

control means for controlling operations within the processor in accordance with a stored program, the program comprising stored instructions selected from a predetermined instruction set;

a plurality of registers for storing calculated values;

addressing means operable under control of the stored instructions to perform addressing operations addressing a data storage space of the processor, at least one said registers being operable as an address register as part of the addressing means for storing calculated address values for use in said addressing operations;

a common arithmetic unit having input and output data paths each of width n bits, and being operable under control of the stored instructions both to calculate general data values in co-operation with the registers, and to calculate address values in co-operation with said address register;

wherein

at least one of said registers is operable as a wide data register of width substantially greater than n bits for storing results of arithmetic operations wider than n bits; and

a shifting circuit of said greater width is interposed between the output path of the arithmetic unit and the wide data register, with a feedback path also of said greater width from data outputs of the wide data register, and is operable under control of the stored instructions to generate a shifted result of said greater width in the wide data register in response to at least a multiplication, division or normalisation instruction, by repeated operation of the arithmetic unit in cooperation with the shifting circuit and the wide data register.

2. A processor according to claim 1, wherein said wide data register comprises a pair of data registers (AH, AL) each of width n, independently connectable to an input or output path of said arithmetic unit.

3. A processor according to claim 1, wherein said control means is responsive to a predetermined multiplication instruction to control the arithmetic unit, the shifting circuit and the wide data register so as to multiply two values of width n bits, the result being obtained in the register after plural operating cycles of the arithmetic unit and the shifting circuit, the number of cycles being independent of the actual values being multiplied.

4. A processor according to claim 1, wherein said control means is responsive to a predetermined division instruction to control the arithmetic unit, the shifting circuit and the register so as to divide two values of width n bits, the quotient and remainder being obtained in the wide data register after plural operating cycles of the arithmetic unit and the shifting circuit, the number of cycles being independent of the actual values being divided.

5. A processor according to claim 1, wherein the shifting circuit can perform only single bit position shifting per operating cycle.

6. A processor according to claim 1, formed in an integrated circuit together with program storage and data storage space addressable independently via respective address buses of the processor, wherein the processor is arranged to execute instructions that have been selected from the instruction set and stored in the program storage space of the integrated circuit.

7. A processor according to claim 1, wherein the instruction of the instruction set are of fixed length.

8. A processor according to claim 1, wherein the execution of each instruction takes a number of processor execution cycles, dependent on the type of instruction, and wherein a further instruction is not executable until such instructions are completely executed.

9. A processor according to claim 1, wherein, to the extent that it can be provided under program control, data communication externally of the processor is possible only via the data storage address space.

10. A processor according to claim 1, wherein an instruction to store data from one of said data registers to said data storage space is executed using a data path not including the arithmetic unit.

11. A processor according to claim 1, wherein dedicated unidirectional data paths are provided (i) between the register outputs and an input path of the arithmetic unit and (ii) between the arithmetic unit output data path and the register input.

12. A processor according to claim 11, wherein a further dedicated path is provided to one address register (X) of the processor from a program counter register (PC), said data path including an incrementer, so as to store a subroutine return address.

13. A processor according to claim 1, without an interrupt routine execution handling facility.

14. A processor according to claim 1, further comprising an interface for receiving a communication request from external circuitry, the processor being responsive to such a communication request only during predetermined time periods during normal program controlled operation.

15. A processor according to claim 14, wherein said predetermined periods are defined by inclusion of a predetermined communication instruction in the stored program.

16. A processor according to claim 1, wherein the processor has at least one external control line, and wherein at least one instruction of the instruction set is decoded differently depending on a signal present on the external control line.

17. A processor according to claim 1, wherein the processor has a basic instruction cycle sub-divided into plural internal clock states, and wherein, for at least one combinational logic circuit having plural input lines and functioning under control of each stored program, means are provided to sample and latch input values for the combinational logic circuit only at a defined state or states within the instruction cycle.

18. A processor according to claim 17, wherein said combinational logic circuit comprises the arithmetic unit of the processor.

19. A processor according to claim 18, wherein said combinational logic circuit further comprises an instruction decoding circuit of the control means.

20. A processor according to claim 1, wherein n is sixteen.

21. A processor according to claim 1, adapted to operate under control of a program including a pre-stored linear sequence of instructions and a high frequency clock signal, the processor further comprising means for implementing a state of low power consumption in which execution of said program is suspended, and means for ending said suspended state so that execution of said program continues from the next instruction in the stored sequence without execution of instructions stored outside said sequence.

22. A processor according to claim 21, wherein said suspended state is entered in accordance with a signal (WAKE_UP) applied to the processor, but only at a point in the instruction sequence defined by inclusion of a specific instruction.

23. A processor according to claim 1, adapted to operate synchronously under control of a high frequency clock signal, the processor further comprising:

means for imposing a state of low power consumption in which execution of said program is suspended and said clock signal is isolated from the processor circuitry, while the clock signal continues running; and

monitoring means responsive to any of a plurality of external signals for ending said suspended state by re-applying said clock signal to the processor,

wherein said monitoring means comprises;

plural individual monitoring circuits for detecting predetermined changes in respective ones of the external signals; and

a common trigger circuit responsive to outputs of the individual monitoring circuits for re-applying said clock signal to the processor,

and wherein the individual monitoring circuits, but not the common trigger circuit, are isolated from the running clock signal during said suspended state.

24. A processor according to claim 23, wherein at least one of said individual monitoring circuits comprises:

means responsive to said clock signal prior to the suspended state for storing a value of the corresponding external signal; and

asynchronous circuit means for, during the suspended state, comparing the external signal with the stored value.

25. A processor according to claim 1, wherein the integrated circuit has at least one external control line (RUN_STEP), and wherein at least one instruction (BRK) of the instruction set is an instruction which will either halt the program-controlled processing operations or will effect no meaningful operation, depending on said signal.

26. A processor according to claim 25, comprising means (RUN_STEP) for signalling externally that execution has been halted.