MicroBlaze Processor Reference Guide 275
UG984 (v2018.2) June 21, 2018 www.xilinx.com
Chapter 5: MicroBlaze Instruction Set Architecture
rsubi
Arithmetic Reverse Subtract Immediate
rsubi
rD, rA, IMM
Subtract Immediate
rsubic
rD, rA, IMM
Subtract Immediate with Carry
rsubik
rD, rA, IMM
Subtract Immediate and Keep Carry
rsubikc
rD, rA, IMM
Subtract Immediate with Carry and Keep Carry
0 0 1 K C 1 rD rA IMM
0 6 11 16
31
Description
The contents of register rA is subtracted from the value of IMM, sign-extended to 32 bits, and the
result is placed into register rD. Bit 3 of the instruction (labeled as K in the figure) is set to one for the
mnemonic rsubik. Bit 4 of the instruction (labeled as C in the figure) is set to one for the mnemonic
rsubic. Both bits are set to one for the mnemonic rsubikc.
When an rsubi instruction has bit 3 set (rsubik, rsubikc), the carry flag will Keep its previous value
regardless of the outcome of the execution of the instruction. If bit 3 is cleared (rsubi, rsubic), then the
carry flag will be affected by the execution of the instruction. When bit 4 of the instruction is set to
one (rsubic, rsubikc), the content of the carry flag (MSR[C]) affects the execution of the instruction.
When bit 4 is cleared (rsubi, rsubik), the content of the carry flag does not affect the execution of the
instruction (providing a normal subtraction).
Pseudocode
if C = 0 then
(rD) ← sext(IMM) + (rA) + 1
else
(rD)
← sext(IMM) + (rA) + MSR[C]
if K = 0 then
MSR[C] ← CarryOut
Registers Altered
•rD
•MSR[C]
Latency
• 1 cycle
Note
In subtractions, Carry = (Borrow). When the Carry is set by a subtraction, it means that there is no
Borrow, and when the Carry is cleared, it means that there is a Borrow. By default, Type B Instructions
will take the 16-bit IMM field value and sign extend it to 32 bits to use as the immediate operand. This
behavior can be overridden by preceding the Type B instruction with an imm instruction. See the
instruction
“imm” for details on using 32-bit immediate values.
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