Hi Philip,
Sorry to bother you, I think your explanation makes sense to me.
However, if the strength field can give you the RSSI value when
receiving the packet, why fetching the RSSI register just gives you the
noise floor. Could you also give me a clue how the value of the strength
field in TOSMsg is generated based on the RSSI register please? Many thanks!
Best regards,
Ruoshui
Philip Levis wrote:
On Jan 15, 2008, at 4:25 AM, Ruoshui Liu wrote:
Dear all,
I am trying to measure the RSSI value in TinyOS 1.x. However, I have
got two totally different values when I applied two methods to do
this, one is to read the 'strengh field' in the TOSMsg as the MPR/MIB
manual suggests, and the other one is to read the RSSI_VAL register.
I am wondering why I have obtained such different values, for example,
before adding the offset value (-45): the reading from the 'strengh
field' is -20; the reading from the RSSI_VAL register is -53;
after adding the offset value (-45): the reading from the 'strengh
field' is - 65; the reading from the RSSI_VAL register is -98.
I am really confused, could anyone help me with the reason for this
pleaes?
The strength field is the RSSI of a received packet. If you read the
RSSI register, then you might be sampling the RSSI when you are *not*
receiving a packet, at which point it is the hardware noise floor. -98
dBm is a reasonable hardware noise floor for a cc2420-based node.
Phil
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