At 8:52am on Mar 22, electrons from David Moss conveyed:
> All structures must be created to enforce word alignment. You'll probably
> notice another problem if you construct an array of these
> DimmerControlMSG's, because word-alignment will be off due to the uint8_t.
Can you elaborate more on this (problem with array). Because
I had used structures like
struct a {
uint8_t f1;
uint32_t f2;
};
knowing that msp will add a padding byte between f1 and f2
and have found it to work.
Thanks,
Sumit
>
> A rule of thumb is always create structs with the biggest variables first to
> the smallest variables last, always have an even number of bytes, and never
> use the packed attribute:
>
> struct MyStruct {
> uint32_t bigvar1;
> uint32_t bigvar2;
> uint16_t mediumvar1;
> uint8_t smallvar1;
> uint8_t smallvar2;
> } MyStruct;
>
> Sorry I didn't point this issue out to you yesterday, I didn't realize the
> actual layout of the struct was what was getting in your way.
>
> David
>
>
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of Jose L.
> Ponce
> Sent: Wednesday, March 22, 2006 8:42 AM
> To: [email protected]
> Subject: Re: [Tinyos-help] Strange results when sending uint16_t
> values.(SOLVED)
>
>
> Hi,
>
> I was able to solve the problem:
>
> I noticed that there was something wrong with the uint16 field: I
> programmed the mote to unpack the message and pack it in another one to
> be sent back to the computer. If I sent 0x0a05 the return message would
> be 0x0a00. I tried to divide the uint16 field in two uint8 fields (high
> and low), and with that everything worked.
>
> To cut a long story short, after a long hours of desperation, I did the
> simplest thing I could think of. If my message structure was:
>
> struct DimmerControlMSG
> {
> uint8_t todo;
> uint16_t val;
> };
>
> I changed it for:
>
> struct DimmerControlMSG
> {
> uint16_t val;
> uint8_t todo;
> };
>
> And now everything's working!!
>
> Any comments on this? Is this something which happens often?
>
> -Jose.
>
> On Tue, 2006-03-21 at 18:04 +0100, Jose L. Ponce wrote:
> > Hi all,
> >
> > I want to control the DAC of my telosb mote using commands from the
> > computer through the USB port. For that, I've programmed an application
> > which receives a message with two fields: uint8_t for the command and
> > uint16_t for the value we want to set the DAC to.
> >
> > There are two commands: set (1), with a value, to set the DAC, and show,
> > without a value, to see to which value the DAC is set to (when issuing a
> > set command, the mote returns the DAC value as well).
> >
> > On the computer side, the commands are issued using a small java
> > application:
> >
> > java Dimmer set X
> > java Dimmer show
> >
> > The problem is that the value field (uint16_t) is not recognised: I will
> > issue java Dimmer set 10 ten times and each time I will get a different
> > DAC output and a different return value from the mote. I have tried to
> > modify my message type and have the value field as a uint8_t. In this
> > way, issuing a set command from 0 to 256 will give me right values.
> > Above that, it doesn't seem to work anymore.
> >
> > Can anyone enlighten me a little on what I am doing wrong? It'd be much
> > appreciated.
> >
> > Below I include the relevant code.
> >
> > Thanks,
> >
> > - Jose.
> >
> > // DimmerControlM.nc (on the mote)
> > // DimmerControlMSG has two fields: todo (uint8_t) and value (uint16_t)
> >
> > task void sendMsg(){
> > struct DimmerControlMSG* sen;
> > sen = (struct DimmerControlMSG *)outw.data;
> > sen->value = value;
> >
> > call SendMsg.send( TOS_UART_ADDR, sizeof(struct DimmerControlMSG),
> &outw);
> > }
> >
> > event TOS_MsgPtr ReceiveMsg.receive( TOS_MsgPtr inw ){
> > struct DimmerControlMSG* rec;
> > rec = (struct DimmerControlMSG *)inw->data;
> >
> > if( rec->todo & 0x1 ) {
> > value=rec->value;
> > if(call DAC.output(value) == SUCCESS)
> > call Leds.redToggle();
> > }
> >
> > post sendMsg();
> > return inw;
> > }
> >
> >
> > _______________________________________________
> > Tinyos-help mailing list
> > [email protected]
> > https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
> >
>
>
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