一、数据帧格式

1.1 起始帧

格式1（128byte）：SOH 00 FF filename[ ] filezise[ ] NUL[ ] CRCH CRCL

格式2（1k byte）：STX 00 FF filename[ ] filezise[ ] NUL[ ] CRCH CRCL

SOH/STX:数据包类型：128/1k
00 FF:帧序以及其反码
filename[ ]：文件名，ascii码，末尾跟00表述结束
filezise[ ]：文件大小，ascii码，末尾跟00表述结束
NUL[ ]：数据填充
CRCH CRCL：crc校验，高位在前，低位在后，只校验数据部分

1.2 数据帧

格式1（128byte）：SOH 01 FE data[128] CRCH CRCL

格式2（1k byte）：STX 01 FE data[1024] CRCH CRCL

文件小于128字节：SOH 01 FE data[ ] 1A...1A CRCH CRCL
文件剩余小于128字节：SOH [num] [~~num] data[ ] 1A...1A CRCH CRCL

1.3 结束帧

格式：SOH 00 FF NUL[128] CRCH CRCL

00 FF:帧序以及其反码（固定）
NULL[]：数据空填充

二、文件传输流程

发送端-------------------------------------------------------------------接收端

SOH 00 FF "foo.c" "1064'' NUL[118] CRC CRC >>>>>>>>>>>>>

STX 01 FE data[1024] CRC CRC>>>>>>>>>>>>>>>>>>>>>>>>

STX 02 FD data[1024] CRC CRC>>>>>>>>>>>>>>>>>>>>>>>

STX 03 FC data[1024] CRC CRC>>>>>>>>>>>>>>>>>>>>>>>

STX 04 FB data[1024] CRC CRC>>>>>>>>>>>>>>>>>>>>>>>

SOH 05 FA data[100] 1A[28] CRC CRC>>>>>>>>>>>>>>>>>>

EOT >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

EOT>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

SOH 00 FF NUL[128] CRC CRC >>>>>>>>>>>>>>>>>>>>>>>

注意：

EOT信号由发送端发送
CA中止传输信号也有发送端发送

2.1 传输符号表

符号	数值	含义
SOH	0x01	128字节数据包
STX	0x02	1024字节数据包
EOT	0x04	结束传输
ACK	0x06	回应
NAK	0x15	不回应
CA	0x18	传输中止
C	0x43	请求数据包

三、CRC校验源码

static const rt_uint16_t ccitt_table[256] = {0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7,0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF,0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6,0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE,0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485,0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D,0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4,0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC,0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823,0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B,0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12,0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A,0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41,0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49,0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70,0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78,0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F,0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067,0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E,0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256,0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D,0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C,0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634,0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB,0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3,0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A,0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92,0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9,0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1,0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8,0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0
};
rt_uint16_t CRC16(unsigned char *q, int len)
{rt_uint16_t crc = 0;while (len-- > 0)crc = (crc << 8) ^ ccitt_table[((crc >> 8) ^ *q++) & 0xff];return crc;
}