Actually, all the chips get the convert command (it's directory-specific, so
DS2409 branches won't get the convert unless requested specifically).
When later going to read a temperature, the following algorithm is used:
1. If there is a cached value that hasn't expired, it iis used.
2. If the device is unpowered, a conversion is issued,
a. The bus locked for the full conversion time.
b. The thread pauses for the full time.
c. The value is then read (and cached).
3. If the device is powered, and a simultaneous was done recently, the
value is read immediately.
a. The request waits until the conversion started by "simultaneous"
is ready.
b. The value is cached.
4. If the device is powered, and no valid "simultaneous" was done, a
convert is issued.
a. Since the device is powered, the bus is NOT locked for the full
time
b. The DEVICE is locked, until the conversion is done
c. The device reading thread pauses until the conversion is done.
d. The value is then read (and cached).
Paul Alfille
________________________________
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Ben Griffith
Sent: Monday, December 11, 2006 9:35 PM
To: [EMAIL PROTECTED]; owfs-developers@lists.sourceforge.net
Subject: Re: [Owfs-developers] temperature sensors - simultaneous
and"pre-reading"
I just tried it by adding an unpowered sensor to my net and doing the
following...
echo 1 > simultaneous/temperature
cat 10.*/temperature
The result was that it paused to do the conversion on the one unpowered sensor,
and all the powered ones came up right away. The unpowered sensor probably
tries to do the conversion with all the powered ones, but since the data bus
isn't being held high the conversion fails.
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