When studying the mavlink2 protocol of PX4, when calculating the checksum, a CRC_EXTRA needs to be added to participate in the calculation (but CRC_EXTRA does not participate in data transmission and is only used to calculate the checksum). However, the definition of CRC_EXTRA of mavlink2 has not been found online. array.
Later I found it in the files generated by the build. The last file called common.h, I used the Heli H7 board, and its path was PX4-Autopilot.7z\PX4-Autopilot\build\holybro_kakuteh7_default\mavlink\ common\common.h, the MAVLINK_MESSAGE_CRCS defined in it is extracted at the end of the article. The compiled firmware should be very similar.
The first element of each array inside is the mavlin_CDM serial number. You can find it in Choose a language · MAVLink Developer Guide on their official website. For example, the first element of the ninth array is 11. You can find this by searching for #11 on the official website. Which instruction the array represents. Another example is when monitoring the communication between the qgc ground station and the flight control, the data packet captured when inputting the commander arm through the ground station mavlink console. The command ID is 0x7E, which is 0d126. If you search for #126 on the official website, you will get:
SERIAL_CONTROL ( #126 )
[Message] Control a serial port. This can be used for raw access to an onboard serial peripheral such as a GPS or telemetry radio. It is designed to make it possible to update the devices firmware via MAVLink messages or change the devices settings. A message with zero bytes can be used to change just the baudrate.
#define MAVLINK_MESSAGE_CRCS {
{0, 50, 9, 9, 0, 0, 0},
{1, 124, 31, 43, 0, 0, 0},
{2, 137, 12, 12, 0, 0, 0},
{4, 237, 14, 14, 3, 12, 13},
{5, 217, 28, 28, 1, 0, 0},
{6, 104, 3, 3, 0, 0, 0},
{7, 119, 32, 32, 0, 0, 0},
{8, 117, 36, 36, 0, 0, 0},
{11, 89, 6, 6, 1, 4, 0},
{20, 214, 20, 20, 3, 2, 3},
{21, 159, 2, 2, 3, 0, 1},
{22, 220, 25, 25, 0, 0, 0},
{23, 168, 23, 23, 3, 4, 5},
{24, 24, 30, 52, 0, 0, 0},
{25, 23, 101, 101, 0, 0, 0},
{26, 170, 22, 24, 0, 0, 0},
{27, 144, 26, 29, 0, 0, 0},
{28, 67, 16, 16, 0, 0, 0},
{29, 115, 14, 16, 0, 0, 0},
{30, 39, 28, 28, 0, 0, 0},
{31, 246, 32, 48, 0, 0, 0},
{32, 185, 28, 28, 0, 0, 0},
{33, 104, 28, 28, 0, 0, 0},
{34, 237, 22, 22, 0, 0, 0},
{35, 244, 22, 22, 0, 0, 0},
{36, 222, 21, 37, 0, 0, 0},
{37, 212, 6, 7, 3, 4, 5},
{38, 9, 6, 7, 3, 4, 5},
{39, 254, 37, 38, 3, 32, 33},
{40, 230, 4, 5, 3, 2, 3},
{41, 28, 4, 4, 3, 2, 3},
{42, 28, 2, 6, 0, 0, 0},
{43, 132, 2, 3, 3, 0, 1},
{44, 221, 4, 5, 3, 2, 3},
{45, 232, 2, 3, 3, 0, 1},
{46, 11, 2, 2, 0, 0, 0},
{47, 153, 3, 4, 3, 0, 1},
{48, 41, 13, 21, 1, 12, 0},
{49, 39, 12, 20, 0, 0, 0},
{50, 78, 37, 37, 3, 18, 19},
{51, 196, 4, 5, 3, 2, 3},
{54, 15, 27, 27, 3, 24, 25},
{55, 3, 25, 25, 0, 0, 0},
{61, 167, 72, 72, 0, 0, 0},
{62, 183, 26, 26, 0, 0, 0},
{63, 119, 181, 181, 0, 0, 0},
{64, 191, 225, 225, 0, 0, 0},
{65, 118, 42, 42, 0, 0, 0},
{66, 148, 6, 6, 3, 2, 3},
{67, 21, 4, 4, 0, 0, 0},
{69, 243, 11, 18, 1, 10, 0},
{70, 124, 18, 38, 3, 16, 17},
{73, 38, 37, 38, 3, 32, 33},
{74, 20, 20, 20, 0, 0, 0},
{75, 158, 35, 35, 3, 30, 31},
{76, 152, 33, 33, 3, 30, 31},
{77, 143, 3, 10, 3, 8, 9},
{80, 14, 4, 4, 3, 2, 3},
{81, 106, 22, 22, 0, 0, 0},
{82, 49, 39, 51, 3, 36, 37},
{83, 22, 37, 37, 0, 0, 0},
{84, 143, 53, 53, 3, 50, 51},
{85, 140, 51, 51, 0, 0, 0},
{86, 5, 53, 53, 3, 50, 51},
{87, 150, 51, 51, 0, 0, 0},
{89, 231, 28, 28, 0, 0, 0},
{90, 183, 56, 56, 0, 0, 0},
{91, 63, 42, 42, 0, 0, 0},
{92, 54, 33, 33, 0, 0, 0},
{93, 47, 81, 81, 0, 0, 0},
{100, 175, 26, 34, 0, 0, 0},
{101, 102, 32, 117, 0, 0, 0},
{102, 158, 32, 117, 0, 0, 0},
{103, 208, 20, 57, 0, 0, 0},
{104, 56, 32, 116, 0, 0, 0},
{105, 93, 62, 63, 0, 0, 0},
{106, 138, 44, 44, 0, 0, 0},
{107, 108, 64, 65, 0, 0, 0},
{108, 32, 84, 92, 0, 0, 0},
{109, 185, 9, 9, 0, 0, 0},
{110, 84, 254, 254, 3, 1, 2},
{111, 34, 16, 18, 3, 16, 17},
{112, 174, 12, 12, 0, 0, 0},
{113, 124, 36, 39, 0, 0, 0},
{114, 237, 44, 44, 0, 0, 0},
{115, 4, 64, 64, 0, 0, 0},
{116, 76, 22, 24, 0, 0, 0},
{117, 128, 6, 6, 3, 4, 5},
{118, 56, 14, 14, 0, 0, 0},
{119, 116, 12, 12, 3, 10, 11},
{120, 134, 97, 97, 0, 0, 0},
{121, 237, 2, 2, 3, 0, 1},
{122, 203, 2, 2, 3, 0, 1},
{123, 250, 113, 113, 3, 0, 1},
{124, 87, 35, 57, 0, 0, 0},
{125, 203, 6, 6, 0, 0, 0},
{126, 220, 79, 81, 3, 79, 80},
{127, 25, 35, 35, 0, 0, 0},
{128, 226, 35, 35, 0, 0, 0},
{129, 46, 22, 24, 0, 0, 0},
{130, 29, 13, 13, 0, 0, 0},
{131, 223, 255, 255, 0, 0, 0},
{132, 85, 14, 39, 0, 0, 0},
{133, 6, 18, 18, 0, 0, 0},
{134, 229, 43, 43, 0, 0, 0},
{135, 203, 8, 8, 0, 0, 0},
{136, 1, 22, 22, 0, 0, 0},
{137, 195, 14, 16, 0, 0, 0},
{138, 109, 36, 120, 0, 0, 0},
{139, 168, 43, 43, 3, 41, 42},
{140, 181, 41, 41, 0, 0, 0},
{141, 47, 32, 32, 0, 0, 0},
{142, 72, 243, 243, 0, 0, 0},
{143, 131, 14, 16, 0, 0, 0},
{144, 127, 93, 93, 0, 0, 0},
{146, 103, 100, 100, 0, 0, 0},
{147, 154, 36, 54, 0, 0, 0},
{148, 178, 60, 78, 0, 0, 0},
{149, 200, 30, 60, 0, 0, 0},
{162, 189, 8, 9, 0, 0, 0},
{192, 36, 44, 54, 0, 0, 0},
{225, 208, 65, 73, 0, 0, 0},
{230, 163, 42, 42, 0, 0, 0},
{231, 105, 40, 40, 0, 0, 0},
{232, 151, 63, 65, 0, 0, 0},
{233, 35, 182, 182, 0, 0, 0},
{234, 150, 40, 40, 0, 0, 0},
{235, 179, 42, 42, 0, 0, 0},
{241, 90, 32, 32, 0, 0, 0},
{242, 104, 52, 60, 0, 0, 0},
{243, 85, 53, 61, 1, 52, 0},
{244, 95, 6, 6, 0, 0, 0},
{245, 130, 2, 2, 0, 0, 0},
{246, 184, 38, 38, 0, 0, 0},
{247, 81, 19, 19, 0, 0, 0},
{248, 8, 254, 254, 3, 3, 4},
{249, 204, 36, 36, 0, 0, 0},
{250, 49, 30, 30, 0, 0, 0},
{251, 170, 18, 18, 0, 0, 0},
{252, 44, 18, 18, 0, 0, 0},
{253, 83, 51, 54, 0, 0, 0},
{254, 46, 9, 9, 0, 0, 0},
{256, 71, 42, 42, 3, 8, 9},
{257, 131, 9, 9, 0, 0, 0},
{258, 187, 32, 232, 3, 0, 1},
{259, 92, 235, 235, 0, 0, 0},
{260, 146, 5, 13, 0, 0, 0},
{261, 179, 27, 61, 0, 0, 0},
{262, 12, 18, 22, 0, 0, 0},
{263, 133, 255, 255, 0, 0, 0},
{264, 49, 28, 28, 0, 0, 0},
{265, 26, 16, 20, 0, 0, 0},
{266, 193, 255, 255, 3, 2, 3},
{267, 35, 255, 255, 3, 2, 3},
{268, 14, 4, 4, 3, 2, 3},
{269, 109, 213, 213, 0, 0, 0},
{270, 59, 19, 19, 0, 0, 0},
{271, 22, 52, 52, 0, 0, 0},
{275, 126, 31, 31, 0, 0, 0},
{276, 18, 49, 49, 0, 0, 0},
{280, 70, 33, 33, 0, 0, 0},
{281, 48, 13, 13, 0, 0, 0},
{282, 123, 35, 35, 3, 32, 33},
{283, 74, 144, 144, 0, 0, 0},
{284, 99, 32, 32, 3, 30, 31},
{285, 137, 40, 48, 3, 38, 39},
{286, 210, 53, 57, 3, 50, 51},
{287, 1, 23, 23, 3, 20, 21},
{288, 20, 23, 23, 3, 20, 21},
{290, 251, 46, 46, 0, 0, 0},
{291, 10, 57, 57, 0, 0, 0},
{299, 19, 96, 98, 0, 0, 0},
{300, 217, 22, 22, 0, 0, 0},
{301, 243, 58, 58, 0, 0, 0},
{310, 28, 17, 17, 0, 0, 0},
{311, 95, 116, 116, 0, 0, 0},
{320, 243, 20, 20, 3, 2, 3},
{321, 88, 2, 2, 3, 0, 1},
{322, 243, 149, 149, 0, 0, 0},
{323, 78, 147, 147, 3, 0, 1},
{324, 132, 146, 146, 0, 0, 0},
{330, 23, 158, 167, 0, 0, 0},
{331, 91, 230, 233, 0, 0, 0},
{332, 236, 239, 239, 0, 0, 0},
{333, 231, 109, 109, 0, 0, 0},
{334, 72, 10, 10, 0, 0, 0},
{335, 225, 24, 24, 0, 0, 0},
{336, 245, 84, 84, 0, 0, 0},
{339, 199, 5, 5, 0, 0, 0},
{340, 99, 70, 70, 0, 0, 0},
{350, 232, 20, 252, 0, 0, 0},
{360, 11, 25, 25, 0, 0, 0},
{370, 75, 87, 109, 0, 0, 0},
{373, 117, 42, 42, 0, 0, 0},
{375, 251, 140, 140, 0, 0, 0},
{380, 232, 20, 20, 0, 0, 0},
{385, 147, 133, 133, 3, 2, 3},
{386, 132, 16, 16, 3, 4, 5},
{387, 4, 72, 72, 3, 4, 5},
{388, 8, 37, 37, 3, 32, 33},
{390, 156, 238, 238, 0, 0, 0},
{395, 0, 212, 212, 0, 0, 0},
{397, 182, 108, 108, 0, 0, 0},
{400, 110, 254, 254, 3, 4, 5},
{401, 183, 6, 6, 3, 4, 5},
{410, 160, 53, 53, 0, 0, 0},
{411, 106, 3, 3, 0, 0, 0},
{412, 33, 6, 6, 3, 4, 5},
{413, 77, 7, 7, 3, 4, 5},
{9000, 113, 137, 137, 0, 0, 0},
{9005, 117, 34, 34, 0, 0, 0},
{12900, 114, 44, 44, 3, 0, 1},
{12901, 254, 59, 59, 3, 30, 31},
{12902, 140, 53, 53, 3, 4, 5},
{12903, 249, 46, 46, 3, 0, 1},
{12904, 77, 54, 54, 3, 28, 29},
{12905, 49, 43, 43, 3, 0, 1},
{12915, 94, 249, 249, 3, 0, 1},
{12918, 139, 51, 51, 0, 0, 0},
{12919, 7, 18, 18, 3, 16, 17},
{12920, 20, 5, 5, 0, 0, 0}}
#endif