S12 / MagniV MicrocontrollersのトピックS12Z 32bit struct with bitfields

S12Z 32bit struct with bitfields

ecorini — Thu, 07 Sep 2017 10:30:40 GMT

Hello,

I'm using S12Z microcontroller on CW 10.6 with these code generation options:

Memory Model: Small

Bit-field gap limit: 255

Bit-filed byte allocation from LSB to MSB: enabled

Bit-filed type size reduction: disabled

This struct:

typedef struct _TestStruct
{
unsigned long field1 : 1;
unsigned long filed2 : 31;
} tTestStruct;

has size of 5bytes in map file. What is the reason?

thanks for your response!

Re: S12Z 32bit struct with bitfields

lama — Mon, 11 Sep 2017 09:01:27 GMT

Hi,

the issue is being solved. There were some test done and it was reported to a CodeWarrior application team.

now it looks like "feature" but unacceptable. The CW Apps engineer has promised to get some info.

Best regards,

Ladislav

Re: S12Z 32bit struct with bitfields

stanish — Tue, 12 Sep 2017 13:47:50 GMT

Hello,

Thanks for the question.

I've discussed this behavior with our compiler expert.

It is caused by the S12Z compiler behavior when allocating structures. It allocates bitfields within 8 and 16-bit wide (with direct impact from the options described in the compiler manual). Everything that exceeds 16 bit is allocated as a different field.

The bitfield allocation unit is byte and if things don't fit in byte (or too large gaps), the allocation can be extended to word. For 3 or 4 bytes, the allocation is done differently and does not allow merging other fields in a bitfield larger than a word (2-bytes)

So no matter how you arrange the structure, or the bit-field options you use, a bitfield larger than 16-bits will always be allocated alone.

Hope it helps to clarify this issue.

Stan

Re: S12Z 32bit struct with bitfields

ecorini — Mon, 18 Sep 2017 06:28:20 GMT

Thank you for the reply