Instruction encoding for system register bit set and clear
View Patent ↗An instruction encoding architecture is provided for a microprocessor to allow atomic modification of privileged architecture registers. The instructions include an opcode that designates to the microprocessor that the instructions are to execute in privileged (kernel) state only, and that the instructions are to communicate with privileged control registers, a field for designating which of a plurality of privileged architecture registers is to be modified, a field for designating which bit fields within the designated privileged architecture register is to be modified, and a field to designate whether the whether the designated bit fields are to be set or cleared. The instruction encoding allows a single instruction to atomically set or clear bit fields within privileged architecture registers, without reading the privileged architecture registers into a general purpose register. In addition, the instruction encoding allows a programmer to specify whether the previous content of a privileged architecture register is to be saved to a general purpose register during the atomic modification.
1. A microprocessor having an architecture register that is modifiable by an instruction, the microprocessor comprising:
an execution core, for receiving the instruction and for modifying the architecture register upon execution of the instruction,
wherein the instruction comprises:
a first operand that is an immediate value to specify a particular bit field within the architecture register to be modified upon execution of the instruction;
a second operand to identify the architecture register to be modified; and
a third operand to specify whether the particular bit field is to be set or cleared; and
whereby the architecture register is modified atomically when the instruction executes.
2. The microprocessor recited in claim 1 , wherein the execution core is further configured to copy one or more bits of the architecture register to a general purpose register in response to executing the instruction.
3. The microprocessor recited in claim 1 , wherein the architecture register is directly modified by the instruction without requiring one or more bits of the architecture register to first be moved to a general purpose register.
4. The microprocessor recited in claim 1 , wherein the instruction is configured to set the particular bit field in the architecture register as specified by the second operand.
5. The microprocessor recited in claim 1 , wherein the instruction is configured to clear the particular bit field in the architecture register as specified by the second operand.
6. The microprocessor recited in claim 5 , wherein said instruction clears bit fields in the architecture register according to a value of said first operand.
7. The microprocessor recited in claim 1 , wherein the instruction comprises an opcode to specify that an atomic update to the architecture register is requested.
8. The microprocessor recited in claim 1 , wherein the architecture register comprises an interrupt enable bit field to indicate to the microprocessor whether interrupts are enabled or disabled.
9. The microprocessor recited in claim 8 , wherein said interrupt enable bit field indicates to the microprocessor that if the interrupts are disabled, the microprocessor will ignore further interrupts.
10. A method for modifying an architecture register in a microprocessor having an architecture register, comprising:
decoding an instruction comprising:
an immediate value to specify a particular bit field within the architecture register;
a second operand to identify the architecture register to be modified; and
a third operand to specify whether the particular bit field is to be set or cleared; and
executing an instruction to atomically modify the specified particular bit field within the architecture register.
11. The method recited in claim 10 , further comprising copying one or more bits of the architecture register to a general purpose register.
12. The method recited in claim 10 , wherein executing the instruction directly modified the architecture register without requiring one or more bits of the architecture register to first be moved to a general purpose register.
13. The method recited in claim 10 , wherein executing the instruction sets the particular bit field in the architecture register as specified by the second operand.
14. The method recited in claim 10 , wherein executing the instruction clears the particular bit field in the architecture register as specified by the second operand.
15. The method recited in claim 14 , wherein said instruction clears bit fields in the architecture register according to a value of said first operand.
16. The method recited in claim 10 , wherein the instruction comprises an opcode to specify that an atomic update to the architecture register is requested.
17. The method recited in claim 10 , wherein the architecture register comprises an interrupt enable bit field to indicate to the microprocessor whether interrupts are enabled or disabled, further comprising ignoring interrupts in accordance with the interrupt enable bit field.
18. A microprocessor having an architecture register that is modifiable by an instruction, the microprocessor comprising:
an execution core, for receiving the instruction and for modifying the architecture register upon execution of the instruction, wherein the instruction comprises:
a first operand that is an immediate value to specify a particular bit field within the architecture register to be modified upon execution of the instruction; and
a second operand to specify whether the particular bit field is to be set or cleared; and
whereby the architecture register is modified atomically when the instruction executes.