Xilinx MicroBlaze Reference Manual page 236

Chapter 5: MicroBlaze Instruction Set Architecture
rsubi
Arithmetic Reverse Subtract Immediate
rsubi
rsubic
rsubik
rsubikc
0 0 1 K C 1
0 6
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
Registers Altered
•
•
Latency
•
Notes
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
236
Send Feedback
rD, rA, IMM
rD, rA, IMM
rD, rA, IMM
rD, rA, IMM
rD rA
1
1
if C = 0 then
←
(rD) sext(IMM) +
else
←
(rA)
(rD) sext(IMM) +
if K = 0 then
←
MSR[C] CarryOut
rD
MSR[C]
1 cycle
"imm," page 204
www.xilinx.com
Subtract Immediate
Subtract Immediate with Carry
Subtract Immediate and Keep Carry
Subtract Immediate with Carry and Keep Carry
1
6
(rA) + 1
+ MSR[C]
for details on using 32-bit immediate values.
MicroBlaze Processor Reference Guide
IMM
UG081 (v14.7)
3
1