Processing system and method for executing instructions
A processing system for executing instructions comprises a first part ( 11 ) having address information and a plurality of data bits, E 0 to E N . According to one embodiment, each data bit E 0 to E N directly selects a corresponding element 13 0 to 13 N forming a second part of the instruction set (for example a VLIW). In this manner, the first part ( 11 ) is used to only select elements that do not comprise NOP instructions, thereby avoiding power being consumed unnecessarily. According to an alternative embodiment, different groups of elements in the second part ( 13 ) may be selected by a number encoded in the first part ( 11 ), using data bits E o to E N . Preferably, these different groups reflect the most likely used combinations in a program.
1. A method of executing instructions in a processor in which a first part of an instruction causes execution of a second part of an instruction, and wherein the second part comprises a plurality of elements, the method comprising the steps of:
fetching a first part of the instruction;
identifying from first information encoded in the first part of the instruction which elements constitute the second part of the instruction;
identifying from second information encoded in the first part of the instruction which of the identified elements correspond to no-operation, NOP instructions; and
fetching the elements that form the second part of the instruction, excluding the elements which are identified by the second information as corresponding to no-operation, NOP, instructions.
2. A method as claimed in claim 1 , wherein the second information encoded in the first part comprises a plurality of data bits, each data bit providing information for selecting an associated element of the second part of the instruction.
3. A method as claimed in claim 1 , wherein the second information encoded in the first part comprises a plurality of data bits, the data bits in combination representing an associated group of elements forming the second part of the instruction.
4. A method as claimed in claim 3 , wherein each group of elements in the second part relates to a group of elements that is frequently used during program execution.
5. A method as claimed in claim 1 , wherein the second part is a very long instruction word, VLIW, each element in the VLIW forming an instruction for a functional element of a processor.
6. A method as claimed in claim 1 , wherein the first part is stored in a first memory, and wherein the second part is stored in a second memory.
7. A processing system for executing instructions, wherein a first part of an instruction causes execution of a second part of an instruction, the system comprising:
means for fetching a first part of the instruction;
means for identifying from first information contained in the first part of the instruction which elements constitute the second part of the instruction;
means for identifying from second information encoded in the first part of the instruction which of the identified elements correspond to no-operation, NOP instructions; and
means for fetching the elements that form the second part of the instruction, the means for fetching being adapted to exclude the elements which are identified by the second information as corresponding to no-operation, NOP, instructions.
8. A system as claimed in claim 7 , wherein the second information encoded in the first part comprises a plurality of data bits, and the means fetching is adapted to select an associated element of the second part of the instruction based on a corresponding data bit.
9. A system as claimed in claim 7 , wherein the second information encoded in the first part comprises a plurality of data bits, and the means for fetching is adapted to select a group of elements forming the second part of the instruction, based on the plurality of data bits in the first part.
10. A system as claimed in claim 7 , further comprising decode logic for selecting a group of elements forming the second part of the instruction.
11. A system as claimed in claim 7 , wherein the second part is a very long instruction word, VLIW, each element of the VLIW forming an instruction for a functional element of a processor.
12. A system as claimed in claim 7 , further comprising a first memory for storing the first part of the instruction, and a second memory for storing the second part of the instruction.