Cortex-M4 Devices Generic User Guide: 3.9.1. BFC and BFI

3.9.1. BFC and BFI

Bit Field Clear and Bit Field Insert.

Syntax

BFC{cond} Rd, #lsb, #width

BFI{cond} Rd, Rn, #lsb, #width

where:

cond: Is an optional condition code, see Conditional execution.
Rd: Specifies the destination register.
Rn: Specifies the source register.
lsb: Specifies the position of the least significant bit of the bitfield. lsb must be in the range 0 to 31.
width: Specifies the width of the bitfield and must be in the range 1 to 32−lsb.

Operation

BFC clears a bitfield in a register. It clears width bits in Rd, starting at the low bit position lsb. Other bits in Rd are unchanged.

BFI copies a bitfield into one register from another register. It replaces width bits in Rd starting at the low bit position lsb, with width bits from Rn starting at bit[0]. Other bits in Rd are unchanged.

Restrictions

Do not use SP and do not use PC.

Condition flags

These instructions do not affect the flags.

Examples

    BFC   R4, #8, #12       ; Clear bit 8 to bit 19 (12 bits) of R4 to 0
    BFI   R9, R2, #8, #12   ; Replace bit 8 to bit 19 (12 bits) of R9 with
                            ; bit 0 to bit 11 from R2.

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