ir-nec-decode v0.1.0

Decode NEC IR falling-edge intervals into an address and command.

Application scenarios

• A TV or appliance remote sends NEC frames to an IR receiver.
• A product uses a cheap IR remote for setup or service.
• An IR keypad sends address/command pairs.

Contract

typedef enum { IR_NEC_INVALID = 0, IR_NEC_FRAME = 1, IR_NEC_REPEAT = 2 } ir_nec_result_t;
typedef struct { uint8_t address; uint8_t command; } ir_nec_frame_t;
ir_nec_result_t ir_nec_decode(const uint16_t *intervals_us, uint8_t count, ir_nec_frame_t *frame);

• Input is falling-edge intervals: one leader, then 32 bit intervals (MSB first).
• Leader 12..16 ms; bit 0 0.7..1.5 ms; bit 1 1.8..2.8 ms.
• Address and command complements must match.
• A single 10..12 ms interval is a repeat frame.
• No allocation; O(1) for 33 intervals.

Parameters

• The tolerance windows match common 38 kHz receivers; verify against the chosen part.
• The capture port must time falling edges with microsecond resolution.

Memory and timing

• No state; the caller provides 33 intervals (66 bytes at 16-bit).
• O(1); no division.

Integration

ir_nec_frame_t frame;
if (ir_nec_decode(intervals, 33, &frame) == IR_NEC_FRAME) {
    handle_key(frame.address, frame.command);
}

When not to use

• Raw GPIO levels; a capture port must produce edge intervals.
• RC5, Sony, or other protocols; use the matching decoder.

Verification

make test covers a valid frame, bad bit, bad complement, repeat, and wrong count.

Behavior reference: the NEC protocol and a vendor IR receiver example.

IR_NEC_INVALID = 0,
IR_NEC_FRAME = 1,
IR_NEC_REPEAT = 2

uint8_t address;
uint8_t command;