how to align a char table to 32bit boundry

[T J]

Posted on February 09, 2018 at 01:51

How can I force a char array to align 4 ?

//align 4;

char LoRaTxFrames[8][64];  

char LoRaRxFrames[8][64];

is this a correct method ?

char LoRaTxFrames[8][64];  __attribute__((packed, aligned(4)))

char LoRaRxFrames[8][64];  __attribute__((packed, aligned(4)))

#alignment

[Tesla DeLorean]

Posted on February 09, 2018 at 02:08

Most compilers on ARM align structures and elements on 32-bit boundaries unless you change the packing

#pragma pack(1) // tight packing, ie file structures, or third party data

#pragma pack(4) // normal

[S.Ma]

Posted on February 09, 2018 at 02:13

There should be USB examples for 32 bit aligned 8 bit arrays needs.

Usually, if I need 32 bit aligned, why not creating a type with union of u8[4] and u32 ?

This maybe enough for the linker to get a clue of the 32 bit alignment need.

A quick check with MAP file to find out.

[T J]

Posted on February 09, 2018 at 04:52

My purpose is to validate a packet by hash algorithm.

actually, the array was already aligned, but I wanted to force the alignment to be sure future compilations still work.

I am running a 32bit hash over the buffer, rather than doing the 8bit shuffle.

[AvaTar]

Posted on February 09, 2018 at 07:44

Things like memory alignment are core and toolchain specific, so there is no solution that fits for every environment.

Just to mention that.