CCA is required to determine when it is a good time to
transmit. Also, it's used for low power listening to
determine when a transmitter is nearby. The CC2420 makes
the CCA pin go high when either A) energy is detected on
the channel, B) valid 802.15.4 data is detected on the
channel, or C) Both energy and valid 802.15.4 data is
detected. By default in TinyOS 2.x, the CC2420's
registers are configured to (C).
Before transmitting, a backoff period is set and the CCA
pin is used to see if any other radio is transmitting.
Without the CCA pin, the probability of a collision is
high. The CCA on the uC does not need to be interrupt
driven, just polled.
I believe the SFD pin is used to synchronize receiving an
ack, and time-stamping messages. It does need to be
interrupt driven.
-David
On Wed, 8 Nov 2006 12:01:17 -0600
"Greg Jaman" <[EMAIL PROTECTED]> wrote:
Hi Everyone,
I"m creating a new hardware platform for tinyOS. I
decided on using the
CC2420 as the RF transceiver.
I have connected all the SPI lines and control lines.
But I have a few
questions.
This is my configuration.
- 4 SPI lines: (CSn, SCLK, SI, SO)
- FIFOP: Wired to an external Interrupt
- FIFO: GIO pin
- CCA: GIO pin (Clear Channel
Assessment)
- SFD: GIO pin (Start of Frame Delim)
I plan on using the CC2420 Library in the tinyOS1.x/lib
folder
Are all control pins needed? From analyzing the Micaz
and telos code, It
appears that FIFO is not connected and FIFOP is used to
indicated new data
ready. Which makes sense - I only want to interrupt
when the FIFO data has
past a threshold or when the end of the packet is
noticed.
I don't understand why CCA and SFD are needed? From
what I understand, SFD
is used for transmission, but are any of those required
to be interrupts?
Can anyone help with this?
Greg Jaman
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