Instruction Syntax

Mnemonic	Format	Flags
mfsprg	rD,SPRGn	None

Instruction Encoding

Field	Bits	Description
Primary Opcode	0-5	011111 (0x1F)
rD	6-10	Destination register
rA	11-15	00000 (unused)
rB	16-20	00000 (unused)
XO	22-29	01010110 (0x56)

Operation

rD ← SPRGn

MFSPRG copies the contents of the specified Special Purpose Register General (SPRGn) into the destination register rD.

1. Reads the value from the specified SPRG register
2. Copies it to the destination register rD

Note: SPRG registers are used for temporary storage during exception handling.

Affected Registers

General Purpose Registers (GPRs)

• rD (Destination register) - Loaded with SPRG value

Examples

Basic SPRG Read

# Read SPRG0
mfsprg r3, 0       # r3 = SPRG0

# Read SPRG1
mfsprg r4, 1       # r4 = SPRG1

Exception Handler

# In an exception handler
exception_handler:
mfsprg r3, 0       # Get saved register value
# Process the exception using the saved value

Context Switch

# Save context in SPRG registers
mtsprg 0, r3       # Save r3 in SPRG0
mtsprg 1, r4       # Save r4 in SPRG1
# ... context switch ...
mfsprg r3, 0       # Restore r3 from SPRG0
mfsprg r4, 1       # Restore r4 from SPRG1

Related Instructions

mtsprg (Move to SPRG), mfsrr0 (Move from SRR0), mfsrr1 (Move from SRR1), mfdar (Move from DAR)