ash_protocol.h

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#pragma once
 
#include <cstddef>
#include <cstdint>
 
namespace esphome::ezsp_proxy_tap {
 
// ASH Protocol Constants
static constexpr uint8_t ASH_FLAG_BYTE = 0x7E;        // Frame delimiter
static constexpr uint8_t ASH_ESCAPE_BYTE = 0x7D;      // Escape/substitution byte
static constexpr uint8_t ASH_XOR_BYTE = 0x20;         // XOR mask for escaped bytes
static constexpr uint8_t ASH_SUBSTITUTE_BYTE = 0x18;  // Substitution for invalid bytes
 
static constexpr uint8_t ASH_XON_BYTE = 0x11;     // Resume transmission
static constexpr uint8_t ASH_XOFF_BYTE = 0x13;    // Pause transmission
static constexpr uint8_t ASH_CANCEL_BYTE = 0x1A;  // Discards the partial frame before it
// Sent between frames by sleepy NCPs to signal pending callbacks. No control byte is 0xFF.
static constexpr uint8_t ASH_WAKE_BYTE = 0xFF;
 
static constexpr size_t ASH_MAX_DATA_FIELD_SIZE = 220;
static constexpr size_t MAX_ASH_FRAME_SIZE = 1 + ASH_MAX_DATA_FIELD_SIZE + 2;
 
// The control byte, then the first Data Field byte (an RSTACK's version)
static constexpr size_t ASH_HEADER_SIZE = 2;
 
// Protocol limits
static constexpr uint8_t ASH_MAX_SEQUENCE = 7;  // 3-bit sequence number (0-7)
 
// The frame CRC is CRC-CCITT: crc16be() with this initial value, transmitted big-endian
static constexpr uint16_t ASH_CRC_INIT = 0xFFFF;
 
// FLAG, control byte, two CRC bytes, FLAG. None of the eight ACKs has a byte that needs
// escaping, so the size is fixed.
static constexpr size_t ASH_ACK_FRAME_SIZE = 5;
 
// Writes the ACK frame for `ack_num` into `output`
void ash_build_ack_frame(uint8_t *output, uint8_t ack_num);
 
}  // namespace esphome::ezsp_proxy_tap