Integrated circuit with error repair and fault tolerance

Abstract

An integrated circuit is provided with error detection circuitry and error repair circuitry. Error tolerance circuitry is responsive to a control parameter to selectively disable the error repair circuitry. The control parameter is dependent on the processing performed within the circuit. For example, the control parameter may be generated in dependence upon the program instruction being executed, the output signal value which is in error, the previous behavior of the circuit or in other ways.

1 . An integrated circuit comprising:
 first processing circuitry responsive to an input signal to perform processing to generate an output signal;   second processing circuitry coupled to said first processing circuitry and responsive to said output signal to perform further processing;   error detecting circuitry responsive to said output signal to detect errors in said output signal at a time after said second processing circuitry has started to perform said further processing using said output signal;   error repair circuitry responsive to an error in said output signal detected by said error detecting circuitry to perform an error operation; and   error tolerance circuitry coupled to said error detecting circuitry and responsive to a control parameter selectively to disable said error detecting circuitry such that an error detection operation is not performed; wherein   said control parameter is dependent on at least one of said processing performed by said first processing circuitry and said further processing performed by said second processing circuitry.   
     
     
         2 . An integrated circuit as claimed in  claim 1 , comprising a mode register storing a fault-tolerance mode flag set under program control and wherein said control parameter is said fault-tolerance mode flag. 
     
     
         3 . An integrated circuit as claimed in  claim 2 , comprising a plurality of instances of processing circuitry with associated error detecting circuitry selectively disabled by a corresponding one of a plurality of fault-tolerance mode flags. 
     
     
         4 . An integrated circuit as claimed in  claim 1 , wherein said integrated circuit has a speculative mode of operation in which architectural state is not updated and said control parameter is set to disable said error detecting circuit when said integrated circuit is in said speculative mode. 
     
     
         5 . An integrated circuit as claimed in  claim 1 , comprising a state machine operating to generate said control parameter to match an operating mode of said first processing circuitry and said second processing circuitry. 
     
     
         6 . An integrated circuit as claimed in  claim 1 , wherein said first processing circuitry and said second processing circuitry execute processing operations specified by a program instruction and wherein said control parameter is dependent upon said processing operations specified by said program instruction. 
     
     
         7 . An integrated circuit as claimed in  claim 6 , wherein said control parameter is a fault-tolerance field within said program instruction. 
     
     
         8 . An integrated circuit as claimed in  claim 6 , wherein said program instruction is part of an instruction set comprising a plurality of program instructions, a first group of program instructions of said instruction set being fault-tolerance program instructions for which said control parameter indicates error detection is disabled and a second group of program instructions of said instruction set being precise program instructions for which said control parameter indicates error detection is not disabled. 
     
     
         9 . An integrated circuit as claimed in  claim 1 , comprising a processing pipeline including said first processing circuitry and said second processing circuitry and said error repair operation includes flushing at least part of said processing pipeline. 
     
     
         10 . An integrated circuit as claimed in  claim 1 , wherein said error repair operation includes correcting said further processing performed by said second processing circuitry using said output signal. 
     
     
         11 . An integrated circuit as claimed in  claim 1 , wherein said error detecting circuitry detects a change in a value of said output signal during a predetermined period as indicative of said error. 
     
     
         12 . An integrated circuit as claimed in  claim 11 , wherein said predetermined period extends to after said second processing circuitry has started to perform said further processing using said output signal. 
     
     
         13 . An integrated circuit as claimed in  claim 1 , wherein said control parameter disables said error detecting circuitry when said output signal generated by said processing of said first processing apparatus is part of a data signal. 
     
     
         14 . An integrated circuit as claimed in  claim 1 , wherein said control parameter does not disable said error detecting circuitry when said output signal generated by said processing of said first processing apparatus is part of one of:
 a control signal; and   an address signal.   
     
     
         15 . An integrated circuit comprising:
 first processing means for performing processing to generate an output signal in response to an input signal;   second processing means for performing further processing in response to said output signal, said second processing means being coupled to said first processing means;   error detecting means for detecting errors in said output signal at a time after said second processing means has started to perform said further processing using said output signal;   error repair means for performing an error repair operation in response to an error in said output signal detected by said error detecting means; and   error tolerance means for selectively disabling said error detecting means in response to a control parameter such that said error detection operation is not performed; wherein   said control parameter is dependent on at least one of said processing performed by said first processing means and said further processing performed by said second processing means.   
     
     
         16 . A method of operating an integrated circuit comprising the steps of:
 performing processing to generate an output signal in response to an input signal using first processing circuitry;   performing further processing in response to said output signal using second processing circuitry coupled to said first processing circuitry;   detecting errors in said output signal, using error detecting circuitry, at a time after said second processing circuitry has started to perform said further processing using said output signal;   performing an error repair operation in response to an error in said output signal; and   in response to a control parameter, selectively disabling said error detecting circuitry such that an error detection operation is not performed; wherein   said control parameter is dependent on at least one of said processing performed by said first processing circuitry and said further processing performed by said second processing circuitry.   
     
     
         17 . A method as claimed in  claim 16 , wherein said control parameter is a fault-tolerance mode flag set under program control. 
     
     
         18 . A method as claimed in  claim 17 , comprising a plurality of instances of processing circuitry with associated error detecting circuitry selectively disabled by a corresponding one of a plurality of fault-tolerance mode flags. 
     
     
         19 . A method as claimed in  claim 16 , wherein said integrated circuit has a speculative mode of operation in which architectural state is not updated and said control parameter is set to disable said error detecting circuit when said integrated circuit is in said speculative mode. 
     
     
         20 . A method as claimed in  claim 16 , comprising generating said control parameter with a state machine to match an operating state of said first processing circuitry and said second processing circuitry. 
     
     
         21 . A method as claimed in  claim 16 , wherein said first processing circuitry and said second processing circuitry execute processing operations specified by a program instruction and wherein said control parameter is dependent upon said processing operations specified by said program instruction. 
     
     
         22 . A method as claimed in  claim 21 , wherein said control parameter is a fault-tolerance field within said program instruction. 
     
     
         23 . A method as claimed in  claim 21 , wherein said program instruction is part of an instruction set comprising a plurality of program instructions, a first group of program instructions of said instruction set being fault-tolerance program instructions for which said control parameter indicates error detection is disabled and a second group of program instructions of said instruction set being precise program instructions for which said control parameter indicates error detection is not disabled. 
     
     
         24 . A method as claimed in  claim 16 , wherein said integrated circuit comprises a processing pipeline including said first processing circuitry and said second processing circuitry and said error repair operation includes flushing at least part of said processing pipeline. 
     
     
         25 . A method as claimed in  claim 16 , wherein said error repair operation includes correcting said further processing performed by said second processing circuitry using said output signal. 
     
     
         26 . A method as claimed in  claim 16 , wherein a change in a value of said output signal during a predetermined period is detected as indicative of said error. 
     
     
         27 . A method as claimed in  claim 26 , wherein said predetermined period extends to after said second processing circuitry has started to perform said further processing using said output signal. 
     
     
         28 . A method as claimed in  claim 16 , wherein said control parameter disables said error detecting circuitry when said output signal generated by said processing is part of a data signal. 
     
     
         29 . A method as claimed in  claim 16 , wherein said control parameter does not disable said error detecting circuitry when said output signal generated by said processing is part of one of:
 a control signal; and   an address signal.