[Tinyos-help] Bug report (was: ReadStream period off on a telosb?)

[Sivan Toledo]

You're right, but fixing it didn't help so I dug deeper and found that
the ReadStream implementation on the MSP430 is broken.

The problem is that chips/msp430/adc12/AdcP represents the usecond
period as uint32_t, but its ResourceReadStream.granted event passes
the usecond argument to
Msp430Adc12SingleChannel.configureMultiple, which expects a uint16_t period.

So even if I set the usecond period correctly in my program to a large
value, it gets truncated in this function call. For some reason, GCC
does not complain.

The bug actually goes a bit deeper; it's not a simple matter of
changing the argument of  Msp430Adc12SingleChannel.configureMultiple
to uint32_t, because the argument is eventually used to directy set a
compare register, and the compare registers are 16 bits on the MSP430.
So there is no easy way to fix this except by using a virtual timer or
alarm. Not a good solution.

The bug does not affect me because I need a short period and was just
using the 1 second period as a sanity check, but it is there (and as
far as I could see, there was no warning about it anywhere).

Regards, Sivan

On 3/5/08, Michiel Konstapel <m.konstapel at sownet.nl> wrote:
>
>
>
> In C, integer constants are of type int, which on the MSP is 16 bits. I.e.,
> you're actually sampling every (1000000 & 0xFFFF) clock ticks (are those
> microseconds?). To specify a long integer (32 bit) constant, add an L to the
> number. You can also add a U to make it unsigned: read(1000000UL) should do
> the trick.
>
>  HTH,
>  Michiel
>
>
>  -----Original Message-----
>  From: tinyos-help-bounces at millennium.berkeley.edu on
> behalf of Sivan Toledo
>  Sent: Tue 3/4/2008 9:07 PM
>  To: TinyOS Help Mailing List
>  Subject: [Tinyos-help] ReadStream period off on a telosb?
>
>  I am trying to read from the TelosB ADC using the ReadStream interface
>  (wired to AdcReadStreamClientC), and it seems that when I set a large
>  period, for sanity checking, the actual sampling period is much
>  smaller. For example, if I call read(1000000) when the posted buffers
>  are of size 8, I get several buffers per second back, rather than 1
>  every 8 seconds.
>
>  Any idea why this is happening?
>
>  Thanks, Sivan
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