Sub Extern Function

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Sub Extern

Description - Two different RAW atoms. One is performed if the provided predicate is true, the other is performed if the predicate is false.

Instantiation:

#define REG_READ 8w0
#define REG_WRITE 8w1
#define REG_ADD  8w2
#define REG_SUB  8w3

#define EQ_RELOP    8w0
#define NEQ_RELOP   8w1
#define GT_RELOP    8w2
#define LT_RELOP    8w3
@Xilinx_MaxLatency(1)
@Xilinx_ControlWidth(width(T))
extern void <reg_name>_reg_sub<T, D>(in T index_2,
                                     in D newVal_2,
                                     in D incVal_2,
                                     in bit<8> opCode_2,
				     in T index_1,
				     in D newVal_1,
				     in D incVal_1,
				     in bit<8> opCode_1,
                                     in T index_comp,
				     in D compVal,
                                     in bit<8> relOp,
                                     out D result,
                                     out bit<1> boolean);

• index_2 - the index to access for the 2nd RAW atom.

• newVal_2 - the new value to write into the register at index_2 for the second RAW atom. This field is only used if opCode_2 == REG_WRITE.

• incVal_2 - the amount to add to the register at the index_2 for the second RAW atom. This field is only used if opCode_2 == REG_ADD.

• opCode_2 - defines the operation to perform for the 2nd RAW atom: REG_READ, REG_WRITE, REG_ADD, or REG_SUB.

• index_1 - the index to access for the 1st RAW atom.

• newVal_1 - the new value to write into the register at index_1 for the 1st RAW atom. This field is only used if opCode_1 == REG_WRITE.

• incVal_1 - the amount to add to the register at the index_1 for the 1st RAW atom. This field is only used if opCode_1 == REG_ADD.

• opCode_1 - defines the operation to perform for the 1st RAW atom: REG_READ, REG_WRITE, REG_ADD, or REG_SUB.

• index_comp - the index to use to perform the comparison for the predicate.

• compVal - the value to compare to the current value of the register at index_comp

• relOp - the operation to use to compare compVal to the current value of the register at index_comp. compVal and relOp together define the predicate that decides whether or not the register value will be modified. If the predicate is true then perform RAW 1 otherwise perform RAW 2.

• result - the latest value of the register at either index_1 or index_2 depending on whether or not the predicate is true or false respectively.

• boolean - bit that indicates whether or not the predicate was true (1) or false (0)

• @Xilinx_MaxLatency - allows P4 programmer to specify the number of clock cycles to complete the extern operation.

• @Xilinx_ControlWidth - allows P4 programmer to specify the width of the address space allocated to this register. This usually be equal to the width of the index field so that the control-plane can access all register entries.