Message Pack

For serialization, EmbMessenger uses a modified version of MessagePack. The following table is the list of currently implemented types.

Type	Byte	Example Value	Example Bytes
Positive FixInt	0x00 - 0x7F	42	2A
Null	0xC0	n/a	C0
End Of Message	0xC1	n/a	C1
Bool false	0xC2	false	C2
Bool true	0xC3	true	C3
Float 32	0xCA	3.14159	CA 40 49 0F D0
Error	0xCB	Param Read Error 0x10	CB 10
Unsigned Int 8	0xCC	241	CC F1
Unsigned Int 16	0xCD	‭61731‬	CD F1 23
Unsigned Int 32	0xCE	‭4045620583‬	CE F1 23 45 67
Unsigned Int 64	0xCF	17375808098319191535	CF F1 23 45 67 89 AB CD EF
Signed Int 8	0xD0	-33	D0 DF
Signed Int 16	0xD1	-3805	D1 F1 23
Signed Int 32	0xD2	-249346713	D2 F1 23 45 67
Signed Int 64	0xD3	-1070935975390360081	D3 F1 23 45 67 89 AB CD EF
Negative FixInt	0xE0 - 0xFF	-16	F0

EmbMessenger has placed a few restrictions on MessagePack. It will not cross signed and unsigned ints; meaning you can't write an unsigned int and read it as a signed int, and vice versa. This is to prevent possible misinterpretations of data, e.g. writing 0xBE as a uint8_t intending for it equal 190, but reading it as a int8_t, which would equal -66. EmbMessenger also does not support doubles, this is because not all microprocessors support 64-bit doubles.

EmbMessenger's implementation of MessagePack also supports minimization and expansion of ints. Writing a uint64_t that fits into a uint8_t will be sent as a uint8_t, and you can read a uint8_t into a uint64_t.

Examples

Write

uint64_t uint64_val = 0x89;
messenger.write(uint64_val); // Writes 0xCC 0x89

int64_t int64_val = -16;
messenger.write(int64_val); // Writes 0xF0

Read

uint64_t uint64_val;
messenger.read(uint64_val); // Reads 0xCC 0x89
// uint64_val contains 0x89

int64_t int64_val;
messenger.read(int64_val); // Reads 0xF0
// int64_val contains -16