rmt_item_types.hpp File Reference

RMT related definition and function for RF433. More...

#include <M5UnitComponent.hpp>

Go to the source code of this file.

Namespaces
namespace	m5
	Top level namespace of M5Stack.

Typedefs
using	m5::unit::rf433::container_type = std::vector<uint8_t>
	Container.
using	m5::unit::rf433::item_container_type = std::vector<gpio::m5_rmt_item_t>
	Item container.
using	m5::unit::rf433::communication_identifier_t = uint8_t
	Communication identifier (0-255)

Functions
constexpr uint32_t	m5::unit::rf433::calculateRingBufferSize (const uint32_t payload_size)
	Calculate the minimum ring buffer size required to receive the given payload size.
item_container_type	m5::unit::rf433::encodeManchester (const uint8_t *data, const uint32_t len, const bool MSB=true)
	Encode manchester.
uint16_t	m5::unit::rf433::decodeManchester (uint8_t *buf, const uint16_t buf_size, const m5::unit::gpio::m5_rmt_item_t *data, const uint32_t num, const bool MSB=true)
	Decode manchester.

Variables
constexpr uint8_t	m5::unit::rf433::ProtocolOverhead = 4
	Protocol overhead in bytes: CRC8(1) + ID(1) + Count(1) + Length(1) = 4.
constexpr uint16_t	m5::unit::rf433::RmtRxMaxItems = 6 * 64
	Maximum RMT items receivable in a single frame per platform.
constexpr uint8_t	m5::unit::rf433::MaxPayloadSize
	Theoretical maximum payload size in bytes for the current platform.

Detailed Description

RMT related definition and function for RF433.

Function Documentation

calculateRingBufferSize()

uint32_t m5::unit::rf433::calculateRingBufferSize ( const uint32_t payload_size )

constexpr

Calculate the minimum ring buffer size required to receive the given payload size.

Parameters

payload_size

Payload size in bytes

Returns

Required ring buffer size in bytes

decodeManchester()

uint16_t m5::unit::rf433::decodeManchester	(	uint8_t *	buf,
		const uint16_t	buf_size,
		const m5::unit::gpio::m5_rmt_item_t *	data,
		const uint32_t	num,
		const bool	MSB = true )

Decode manchester.

Parameters

buf	Output buffer
buf_size	Output buffer size
data	RMT data (exclude SOF)
num	Number of the RMT items
MSB	Process from MSB if true

Returns

Decoded count

encodeManchester()

item_container_type m5::unit::rf433::encodeManchester	(	const uint8_t *	data,
		const uint32_t	len,
		const bool	MSB = true )

Encode manchester.

Parameters

data	Input buffer
len	Length of input buffer
MSB	Process from MSB if true

Returns

Encoded container

Variable Documentation

MaxPayloadSize

uint8_t m5::unit::rf433::MaxPayloadSize

constexpr

Initial value:

=
 
 
 
 
 
 
 
    static_cast<uint8_t>((RmtRxMaxItems - 1 ) / 8 - ProtocolOverhead)

Theoretical maximum payload size in bytes for the current platform.

Calculated from RmtRxMaxItems with protocol overhead (4 bytes). This is the theoretical limit based on RMT hardware memory. In practice, AGC noise from the SYN531R receiver consumes RMT items, reducing the usable capacity. Theoretical values:

• ESP32: 43 bytes (practical safe limit ~23 bytes)
• ESP32-S3: 43 bytes (1 mem_block + threshold ISR wrapping; practical safe limit ~23 bytes)
• ESP-IDF 5.x (RMT v2): 255 bytes

  Warning

  When communicating between RMT v1 (ESP-IDF 4.x) and RMT v2 (ESP-IDF 5.x) devices, the payload size must not exceed the receiver's limit. A v2 transmitter can send up to 255 bytes, but a v1 receiver's capacity is much smaller and varies depending on AGC noise conditions. Always limit the payload to the receiver's max_payload_size.

  See also

  UnitSYN531R::config_t::max_payload_size for the configurable runtime limit

RmtRxMaxItems

uint16_t m5::unit::rf433::RmtRxMaxItems = 6 * 64

constexpr

Maximum RMT items receivable in a single frame per platform.

• ESP32 (RMT v1): 6 mem_blocks x 64 = 384 items
• ESP32-S3 (RMT v1): 1 mem_block x 48 = 48 items (threshold ISR wrapping)
• ESP-IDF 5.x (RMT v2): ping-pong/DMA, limited by user buffer only

  Note

  RF433 ASK receivers (SYN531R) generate AGC noise before the SOF, consuming part of the RMT memory. The maximum payload must fit within a single RMT hardware frame to avoid truncation.

  Warning

  ESP32-S3 + ESP-IDF 4.x has a known RMT RX ping-pong bug that may cause memory corruption and crash in noisy RF environments. See https://github.com/espressif/esp-idf/issues/13419 Recommended to use ESP-IDF 5.x (pioarduino) for ESP32-S3. ESP32: 8ch x 64 items, use 6 = 384