Python struct.pack to arduino C

Projects Programming
1

Hi experts,

I am trying to port a python program to an arduino and I strugle to create a network packet. This packet is constructed by struct.pack python routine.
The packet is constructed with this struct.pack argument : !BBHIII16s
Do you know how to build such binary format ?

Regards,

2 
!BBHIII16s

reads as

!

= network (big endian)

BB

= 2 x unsigned char (2 x 1 byte)

H

= unsigned short (1 x 2 bytes)

III

= 3 x unsigned int (3 x 4 bytes)

16s

= char[] --> char array of 16 bytes

struct __attribute__ ((packed)) {
  uint8_t c1;  // 1 byte   - @0
  uint8_t c2;  // 1 byte   - @1
  uint16_t s1; // 2 bytes  - @2 and 3
  uint32_t i1; // 4 bytes  - @4 ,5, 6 and 7
  uint32_t i2; // 4 bytes  - @8, 9, 10, 11
  uint32_t i3; // 4 bytes  - @12 ,13, 14 and 15
  char t[16];  // 16 bytes - @16 to 31
} data;

remember your arduino is little endian so the unsigned short (uint16_t) and unsigned int (uint32_t) will likely need tweaking (permuting bytes) -> read the incoming 32 bytes in a byte buffer, then (counting from 0) flip bytes 2 and 3, and reverse 4 to 7, 8 to 11 and 12 to 15 so that they are in the right little endian mode. Then you can memcpy() the buffer into your struct and all should be aligned (with gcc)

3

Thank you very much ! It worked flawlessly !
I used the bswap builtin to flip the endianess __builtin_bswap16(number);

Regards,

Bertrand

4

Great !