topic Re: 8bit variabile in LPCXpresso IDE

8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:41 GMT

Content originally posted in LPCWare by blasiis on Fri May 25 01:11:23 MST 2012
I use LPC1758
I have change the lpcxpresso from version .3.6.2 to 4.2.2
The problem is with scructure like this:

typedef struct
{
    uint8_t  var1;
    uint8_t  var2;
    uint8_t  var3;
    uint8_t  var4;         
    uint8_t  var5;         
} MY_STRUCT_T;

This structure with LPCXPRESSO 3.6.2 is large 5 byte, with LPCXpresso 4.2.2 is large 8 byte !!!
I cannot find the linker option for packet this struct.
Where is ?

Thanks

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:42 GMT

Content originally posted in LPCWare by Ex-Zero on Fri May 25 01:30:36 MST 2012
http://support.code-red-tech.com/CodeRedWiki/PackedStructs

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:43 GMT

Content originally posted in LPCWare by blasiis on Fri May 25 02:55:26 MST 2012
I have try many syntax, but i have error "useless storage class specifier in empty declaration"

struct MY_STRUCT_T 
{ 
uint8_t  var1;     
uint8_t  var2;     
uint8_t  var3;     
uint8_t  var4;              
uint8_t  var5;          
} __attribute__((packed));

Where is incorrect ?
There isn't a compiler option ?

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:43 GMT

Content originally posted in LPCWare by Ex-Zero on Fri May 25 03:51:22 MST 2012

Quote: blasiis
I have try many syntax, but i have error "useless storage class specifier in empty declaration"

struct MY_STRUCT_T 
{ 
uint8_t  var1;     
uint8_t  var2;     
uint8_t  var3;     
uint8_t  var4;              
uint8_t  var5;          
} __attribute__((packed));

Where is incorrect ?

Nowhere :eek:

struct MY_STRUCT_T
{
uint8_t  var1;
uint8_t  var2;
uint8_t  var3;
uint8_t  var4;
uint8_t  var5;
} __attribute__((packed));

struct MY_STRUCT_T dummy;

typedef struct _MY_STRUCT_T
{
uint8_t  var1;
uint8_t  var2;
uint8_t  var3;
uint8_t  var4;
uint8_t  var5;
} __attribute__((packed))MY_STRUCT_T ;

MY_STRUCT_T dummy;

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:44 GMT

Content originally posted in LPCWare by frame on Fri May 25 03:58:52 MST 2012
That struct padding is probably something like an implicite alignment, to get some next variable starting on a word address.

Things like [B][FONT=Courier New]__attribute__[/FONT][/B] are not standardized C, like padding and alignment in general.
You need to consult your toolchain documentation.

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:45 GMT

Content originally posted in LPCWare by blasiis on Fri May 25 04:54:30 MST 2012

typedef struct MY_STRUCT_T 
{     
uint8_t  var1;     
uint8_t  var2;     
uint8_t  var3;     
uint8_t  var4;              
uint8_t  var5;          
} __attribute__((packed)) MY_STRUCT_T;

MY_STRUCT_T dummy;

This code don't report compiler error, but the dummy var is large 8 byte, not 5 !!

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:45 GMT

Content originally posted in LPCWare by Ex-Zero on Fri May 25 06:34:02 MST 2012

Quote:

By default, GCC does not pack structures so it will in general leave spaces so that things get word aligned. This behavior can be changed by using the "packed" attribute on the structure.

And map file:

Common symbol size file
dummy 0x5 ./src/main.o

If you are not sure what's 'packed' doing (and what not) create an array and read memory contents :)

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:46 GMT

Content originally posted in LPCWare by blasiis on Fri May 25 06:52:20 MST 2012
In the map the dimension is 8
I need a strucyure not array.

 .data.dummy
                0x10000038        0x8 ./src/pippo.o
                0x10000038                dummy

I must modify also a compiler option ?

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:46 GMT

Content originally posted in LPCWare by Ex-Zero on Fri May 25 07:13:47 MST 2012
Don't know which version we are talking about here. My sample was a new 4.2.2_275 / Windows.

But anyway, what do you expect? Packed is used for structs and not for general memory alignment :)

As mentioned above, this can be seen with arrays. Your struct with 5 bytes isn't a good example to show this mechanism.

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:47 GMT

Content originally posted in LPCWare by blasiis on Fri May 25 22:10:02 MST 2012

Quote: Zero

But anyway, what do you expect? Packed is used for structs and not for general memory alignment .

Sorry, but I don't understand, I have used a struct and used it for a dummy variable.
Why it isn't packed ?

Quote: Zero

As mentioned above, this can be seen with arrays. Your struct with 5 bytes isn't a good example to show this mechanism.

I cannot use a array, but a struct for many variable with the same structure.

But anyway, I have a lot of code already written in this way with lpcxpresso version 3.6.2 without attribute and packed at 5 byte.
When I have update the lpcxpresso to 4.2.2 the same source code creates a variable size not packed at 8 byte.
This is the problem ! I don't want change all my source code, I accept to change the common structure definition or compiler option .

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:48 GMT

Content originally posted in LPCWare by Ex-Zero on Sat May 26 02:09:27 MST 2012
http://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html

Quote:
-fpack-struct[=n]

Without a value specified, pack all structure members together without holes. When a value is specified (which must be a small power of two), pack structure members according to this value, representing the maximum alignment (that is, objects with default alignment requirements larger than this are output potentially unaligned at the next fitting location.

[B]Warning:[/B] the -fpack-struct switch causes GCC to generate code that is not binary compatible with code generated without that switch. Additionally, it makes the code suboptimal. Use it to conform to a non-default application binary interface.

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:48 GMT

Content originally posted in LPCWare by gbm on Sat May 26 11:26:03 MST 2012
What's the value returned by sizeof operator for this structure? It should be 5, according to my understanding of C standard. Could you please check it before drawing further conclusions?

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:49 GMT

Content originally posted in LPCWare by atomicdog on Sat May 26 21:27:49 MST 2012

Quote: blasiis
In the map the dimension is 8
I need a strucyure not array.

 .data.dummy
                0x10000038        0x8 ./src/pippo.o
                0x10000038                dummy

I must modify also a compiler option ?

Are you sure you're looking at the correct/updated map file? It works for me.

typedef struct MY_STRUCT_T
{
uint8_t  var1;
uint8_t  var2;
uint8_t  var3;
uint8_t  var4;
uint8_t  var5;
} __attribute__((packed)) MY_STRUCT_T;
volatile MY_STRUCT_T dummy = {1,2,3,4,5};

 *(.data*)
 .data.dummy    0x10000000        0x5 ./src/main.o
                0x10000000                dummy
 *fill*         0x10000005        0x3 00
 .data.msg      0x10000008        0x4 ./src/main.o

arm-none-eabi-gcc -D__REDLIB__ -DDEBUG -DCR_INTEGER_PRINTF -D__CODE_RED -D__USE_CMSIS=CMSISv2p00_LPC11xx -I"C:\Users\John\Documents\RedSuiteNXP_4.1.0_281\workspace\CMSISv2p00_LPC11xx\inc" -Os -g -Wall -c -fmessage-length=0 -fno-builtin -ffunction-sections -fdata-sections -fno-common -std=gnu99 -mcpu=cortex-m0 -mthumb -MMD -MP -MF"src/main.d" -MT"src/main.d" -o"src/main.o" "../src/main.c"

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:49 GMT

Content originally posted in LPCWare by atomicdog on Sun May 27 00:16:25 MST 2012
You need to set optimization to -Os ( optimize for size).
The issue isn't if the struct is packed or not. Since every member in your struct is 8 bits. The packed attribute doesn't remove the trailing bytes. It just removes the padding in between the member variables.

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:50 GMT

Content originally posted in LPCWare by blasiis on Sun May 27 23:38:23 MST 2012

Quote: atomicdog
You need to set optimization to -Os ( optimize for size).

Using -Os the size change to 5 ! Although there are other differences
I don't understand the function of "packed" attribute, as I have not seen differences
__attribute__((packed))

Anyway with no optimization in the LPCXpresso 3.6 I have size 5 and in the LPCXpresso 4.2 is 8 !!!

Thanks All

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:50 GMT

Content originally posted in LPCWare by Rob65 on Mon May 28 00:13:20 MST 2012

Quote: blasiis

Anyway with no optimization in the LPCXpresso 3.6 I have size 5 and in the LPCXpresso 4.2 is 8 !!!

Strange - I just checked on 4.2.2 and your struct is 5 bytes long:

Allocating common symbols
Common symbol       size              file

_extra              0x4               c:/nxp/lpcxpresso_4.2.2_275/lpcxpresso/tools/bin/../lib/gcc/arm-none-eabi/4.5.1/../../../../arm-none-eabi/lib/thumb2\libcr_c.a(initio.o)
[COLOR=Red][B]dummy               0x5               ./src/main.o[/B][/COLOR]
__heaps             0x4               c:/nxp/lpcxpresso_4.2.2_275/lpcxpresso/tools/bin/../lib/gcc/arm-none-eabi/4.5.1/../../../../arm-none-eabi/lib/thumb2\libcr_c.a(__init_alloc.o)
__end_of_heap       0x4               c:/nxp/lpcxpresso_4.2.2_275/lpcxpresso/tools/bin/../lib/gcc/arm-none-eabi/4.5.1/../../../../arm-none-eabi/lib/thumb2\libcr_c.a(__init_alloc.o)
__Ciob              0x140             c:/nxp/lpcxpresso_4.2.2_275/lpcxpresso/tools/bin/../lib/gcc/arm-none-eabi/4.5.1/../../../../arm-none-eabi/lib/thumb2\libcr_c.a(stdio.o)

Optimization is set to "None (-O0)" so there must be something wrong in your setup or project settings.

Rob

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:51 GMT

Content originally posted in LPCWare by atomicdog on Mon May 28 00:28:47 MST 2012

Quote: blasiis
I don't understand the function of "packed" attribute, as I have not seen differences
__attribute__((packed))

If you have a struct with different variable types in it (like char, int, short, and double) then that's when the packed attribute should make the variables consecutive, and without any spacing between the variables. Without the packed attribute a char could basically take up 4 bytes. So the next variable wouldn't be right next to the actually char value. Needing the packed attribute is common with network protocols and needing to transmit data.

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:52 GMT

Content originally posted in LPCWare by atomicdog on Mon May 28 00:35:55 MST 2012
You can also try the -mstructure-size-boundary=n[COLOR=Black] cmd line option[/COLOR]. It's supposed to do what you want. I couldn't get it to work like I thought it should though.

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:52 GMT

Content originally posted in LPCWare by OXO on Tue May 29 00:13:57 MST 2012
#pragma pack(push,1)

struct MY_STRUCT_T
{
uint8_t var1;
uint8_t var2;
uint8_t var3;
uint8_t var4;
uint8_t var5;
}

#pragma pack(pop)

Should work ;)

Re: 8bit variabile

lpcware — Thu, 16 Jun 2016 00:21:53 GMT

Content originally posted in LPCWare by blasiis on Tue May 29 07:04:19 MST 2012

Quote: OXO
#pragma pack(push,1)
Should work ;)

No, unfortunately the size remain at 8 bytes