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The Nios® V processor core supports one address or data match trigger. The trigger registers are accessible using RISC-V csr opcodes or abstract debug commands. The firing of trigger can either enter the Debug Mode or raise a breakpoint exception, which depends on the trigger registers.
|tselect||Trigger Select||Nios® V processor supports one trigger, therefore the processor selects Trigger 0 at default (value set at 0).|
|tdata1||Trigger Data 1||The value of type field is 2 to represent Trigger 0 as an address or data match trigger. Write behavior to tdata registers depends on the dmode field. The remaining bits acts as mcontrol.|
|mcontrol||Match Control||Controls address and data trigger implementation according to action, m, execute, store and load fields. The Nios® V processor does not implement other fields.|
|tdata2||Trigger Data 2||Holds trigger-specific data (virtual address, instruction opcode, data stored or loaded).|
|tinfo||Trigger Info||The value of info field is 4 at default to signify tdata1.type is 2. This implies selected trigger is an address or data match trigger.|
Based on the bit field setting in mcontrol register, Nios® V processor can implement different trigger types after the selected trigger matches the tdata2 register.
|Triggers||Condition||Firing Time||Exception Program Counter|
|Instruction Address Trigger||Program Counter matches tdata2||Before executing the instruction||The processor sets the Machine Exception Program Counter (mepc) to the instruction address (PC).|
|Instruction Opcode Trigger||Instruction opcode matches tdata2||Before executing the instruction|
|Store Address Trigger||Store address matches tdata2||After executing the store instruction||The processor sets the mepc to the next instruction address (PC + 4).|
|Store Data Trigger||Store data matches tdata2||After executing the store instruction|
|Load Address Trigger||Load address matches tdata2||After executing the load instruction|
|Load Data Trigger||Load data matches tdata2||After executing the load instruction|
|Trigger||mcontrol bit fields|
Note: The trigger is disabled in the following situations:
- The Nios® V processor is in debug mode.
- The Nios® V processor is in machine mode, while mcontrol.m or mcontrol.type is 0.
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