MPC574xB/C/G Device Header Files - structure packing

[heathsmith]

Can anyone tell me if structure packing should be used with these file? My target is an MPC5748G and I am using the GreenHills compiler/linker v7.1.4.

I thought that packing with a 1 byte alignment would be the safest option (GHS - #pragma pack(1)) but doing so there were problems detected at run-time. I then tried a 4-byte alignment (#pragma pack(4)) and this worked Ok.

Can anyone tell if there is an assumption about the structure packing?

See:

https://www.nxp.com/downloads/en/libraries/MPC574xB_C_G.zip

Thanks in advance.

[davidtosenovjan]

Screenshot from Power-Arch-32-bit-ABI-supp-1.0-Embedded.pdf:

[davidtosenovjan]

Hi, I know it only from CodeWarrior but never mind, it is the same situation as other compilers are based on same EABI standard. The global setting has an option “Struct Alignment” its description says following:

The Struct Alignment drop-down list has the default selection PowerPC. To conform with the PowerPC EABI and interoperate with third-party object code, this setting should remain PowerPC. Other settings may lead to reduced performance or alignment violation exceptions. If you choose another setting for Struct Alignment, your code may not work correctly. The options available are as follows:

- PowerPC

- 68K

- 68K 4-byte

If PowerPC alignment is chosen, struct content is aligned to content size and may contain padding bytes. Thus, access to such content should not lead in misaligned access.