Data processing circuits and interfaces

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.