LAUNCHXL-F280025C: UNION : unint8_t or unsigned char with 16 bit

Danny Chan

Part Number: LAUNCHXL-F280025C
Other Parts Discussed in Thread: C2000WARE

Hi,

after researching T.I. forum I understand uint8_t or char is 16 bits not 8 bits, therefore below union does not work as expected.

typedef union {
uint32_t longValue;
uint8_t charValue[4];
} unLong;

unLong unLongTemp ;

if ...

unLongTemp.charValue[0] = 135
unLongTemp.charValue[0] = 214
unLongTemp.charValue[0] = 18
unLongTemp.charValue[0] = 0

the unLongTemp.longvalue = 14024839 not expected 1234567 because each charValue is 16 bit wide

now I use below codes instead...

uint8_t i;
uint32_t longValue[4];

for (i=0; i<=charGetIndex; i++)
{
longValue[i] = charBuffer[charGetIndex];
longValue[i] = charBuffer[charGetIndex + i];
longValue[i] = charBuffer[charGetIndex + i];
longValue[i] = charBuffer[charGetIndex + i];
}
return ((longValue[0]<<24&0xFF000000) | (longValue[1]<<16&0x00FF0000) | (longValue[2]<<8&0x0000FF00) | (longValue[3]&0x000000FF))&0xFFFFFFFF;

My question is, how can I use UNION with char / uint8_t is actually 16 bits wide ?

Thanks,

Danny

over 2 years ago

+1 Santosh Jha over 2 years ago

TI__Guru 50531 points

Hi Danny,

If you have installed C2000Ware SDK, please take a look at this header file.

C:/ti/c2000/C2000Ware_4_02_00_00/device_support/f28002x/headers/include/f28002x_sysctrl.h

This file defines the unions and structures for system control.

Hope it helps.

Regards, Santosh

0 Danny Chan over 2 years ago in reply to Santosh Jha

Intellectual 550 points

Hi Santosh,

thanks for your information, its worked, can you help if I want to use array inside structure ?

below codes OK

struct CHAR_IN_LONG {
uint16_t charValue1:8;
uint16_t charValue2:8;
uint16_t charValue3:8;
uint16_t charValue4:8;
};

typedef union UNLONG {
uint32_t all;
struct CHAR_IN_LONG bit;
} UNLong;

UNLong unLongTemp;

unLongTemp.bit.charValue1 = a_buffer[0]&0xFF;
unLongTemp.bit.charValue2 = a_buffer[1]&0xFF;
unLongTemp.bit.charValue3 = a_buffer[2]&0xFF;
unLongTemp.bit.charValue4 = a_buffer[3]&0xFF;

--------------------------------------------------------------------------------------------------------------

below codes NOT OK

struct CHAR_IN_LONG {
uint16_t charValue[4]:8;
};

typedef union UNLONG {
uint32_t all;
struct CHAR_IN_LONG bit;
} UNLong;

UNLong unLongTemp;

unLongTemp.bit.charValue[0] = a_buffer[0]&0xFF;
unLongTemp.bit.charValue[1] = a_buffer[1]&0xFF;
unLongTemp.bit.charValue[2] = a_buffer[2]&0xFF;
unLongTemp.bit.charValue[3] = a_buffer[3]&0xFF;

regards,

Danny

0 Santosh Jha over 2 years ago in reply to Danny Chan

TI__Guru 50531 points

Danny,

What is the symptom in No-Good condition?

Regards, Santosh

0 Danny Chan over 2 years ago in reply to Santosh Jha

Intellectual 550 points

Santosh Jha said:
What is the symptom in No-Good condition?

when declare array inside struct with bit field, I have got error

error #xxx: invalid type for a bit field

struct CHAR_IN_LONG {
uint16_t charValue[4]:8; // this got error ....
};

typedef union UNLONG {
uint32_t all;
struct CHAR_IN_LONG bit;
} UNLong;

UNLong unLongTemp;

unLongTemp.bit.charValue[0] = a_buffer[0]&0xFF;
unLongTemp.bit.charValue[1] = a_buffer[1]&0xFF;
unLongTemp.bit.charValue[2] = a_buffer[2]&0xFF;
unLongTemp.bit.charValue[3] = a_buffer[3]&0xFF;

0 Santosh Jha over 2 years ago in reply to Danny Chan

TI__Guru 50531 points

Danny,

Requesting compiler expert to take a look at this. We should hear sometime later day/tomorrow.

Regards, Santosh

0 George Mock over 2 years ago in reply to Santosh Jha

TI__Guru**** 245180 points

I think this example is very close to what you need to write.

Fullscreen

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
#include <stdint.h>
typedef union UNLong_tag {
    uint32_t all;
    struct inner_union_tag  {
        uint16_t val : 8;
    } charArray[4];
} UNLong;
int a_buffer[4];
UNLong unLongTemp;
void fxn()
{
    unLongTemp.charArray[0].val = a_buffer[0]&0xFF;
    unLongTemp.charArray[1].val = a_buffer[1]&0xFF;
    unLongTemp.charArray[2].val = a_buffer[2]&0xFF;
    unLongTemp.charArray[3].val = a_buffer[3]&0xFF;
}
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

#include <stdint.h>

typedef union UNLong_tag {
    uint32_t all;
    struct inner_union_tag  {
        uint16_t val : 8;
    } charArray[4];
} UNLong;

int a_buffer[4];
UNLong unLongTemp;

void fxn()
{
    unLongTemp.charArray[0].val = a_buffer[0]&0xFF;
    unLongTemp.charArray[1].val = a_buffer[1]&0xFF;
    unLongTemp.charArray[2].val = a_buffer[2]&0xFF;
    unLongTemp.charArray[3].val = a_buffer[3]&0xFF;
}

Thanks and regards,

-George

0 Danny Chan over 2 years ago in reply to George Mock

Intellectual 550 points

Hi George,

if assign 0x0111 111 (127 decimal) to each val array member, the uint32 all is :

8323199 not excepted 2139062143

typedef union UNLong_tag {
uint32_t all;
struct inner_union_tag {
uint16_t val : 8;
} charArray[4];
} UNLong;

int a_buffer[4];
UNLong unLongTemp;

void fxn()
{
a_buffer[0] = 127;
a_buffer[1] = 127;
a_buffer[2] = 127;
a_buffer[3] = 127;

unLongTemp.charArray[0].val = a_buffer[0]&0xFF;
unLongTemp.charArray[1].val = a_buffer[1]&0xFF;
unLongTemp.charArray[2].val = a_buffer[2]&0xFF;
unLongTemp.charArray[3].val = a_buffer[3]&0xFF;
}

if assign 0xFF (255 decimal) to charArray, the uint32 all is :

16711935 not expected 4294967295

void fxn()
{
a_buffer[0] = 255;
a_buffer[1] = 255;
a_buffer[2] = 255;
a_buffer[3] = 255;

unLongTemp.charArray[0].val = a_buffer[0]&0xFF;
unLongTemp.charArray[1].val = a_buffer[1]&0xFF;
unLongTemp.charArray[2].val = a_buffer[2]&0xFF;
unLongTemp.charArray[3].val = a_buffer[3]&0xFF;
}

Thanks

Danny

0 George Mock over 2 years ago in reply to Danny Chan

TI__Guru**** 245180 points

My previous post is in error. I apologize.

Danny Chan said:
can you help if I want to use array inside structure ?

It is not possible to have an array of anything that is smaller than 16-bits. Thus, the best you can do is something similar to ...

Fullscreen

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
#include <stdint.h>
typedef union UNLong_tag {
    uint32_t all;
    struct inner_union_tag  {
        uint16_t hi : 8;
        uint16_t lo : 8;
    } charArray[2];
} UNLong;
int a_buffer[4];
UNLong unLongTemp;
void fxn()
{
    unLongTemp.charArray[0].hi = a_buffer[0]&0xFF;
    unLongTemp.charArray[0].lo = a_buffer[1]&0xFF;
    unLongTemp.charArray[1].hi = a_buffer[2]&0xFF;
    unLongTemp.charArray[1].lo = a_buffer[3]&0xFF;
}
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

#include <stdint.h>

typedef union UNLong_tag {
    uint32_t all;
    struct inner_union_tag  {
        uint16_t hi : 8;
        uint16_t lo : 8;
    } charArray[2];
} UNLong;

int a_buffer[4];
UNLong unLongTemp;

void fxn()
{
    unLongTemp.charArray[0].hi = a_buffer[0]&0xFF;
    unLongTemp.charArray[0].lo = a_buffer[1]&0xFF;
    unLongTemp.charArray[1].hi = a_buffer[2]&0xFF;
    unLongTemp.charArray[1].lo = a_buffer[3]&0xFF;
}

I suspect you want to avoid names for the 8-bit wide fields, such as hi and lo in this example. Unfortunately, that is not possible.

Thanks and regards,

-George

0 Danny Chan over 2 years ago in reply to George Mock

Intellectual 550 points

Hi George,

George Mock said:
I suspect you want to avoid names for the 8-bit wide fields, such as hi and lo in this example. Unfortunately, that is not possible.

I am OK with it.

Now I have a question, if I assign 0xFF to each hi and lo, i got signed value.

e.g. if hi lo assigned with 0x7F, the unLongTemp.all is 2139062143 011111111 011111111 011111111 011111111

a_buffer[0] = 0x7F;
a_buffer[1] = 0x7F;
a_buffer[2] = 0x7F;
a_buffer[3] = 0x7F;

however if hi lo assigned with 0xFF, the unLongTemp.all is -1

a_buffer[0] = 0xFF;
a_buffer[1] = 0xFF;
a_buffer[2] = 0xFF;
a_buffer[3] = 0xFF;