onsemi AXM0F343, Руководство пользователя

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AX-ConfigurationUtility User Manual
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32
SFD
expected
PKT
expected
SFD
timeout
axradio_sync_slave_rxadvance
axradio_sync_xoscstartup axradio_sync_slave_rxwindow
rx_margin rx_margin rx_startup
SFD
expected
PKT
expected
SFD
timeout
RX EN
RX ready
dt_SFD
tt_SFD
11.3. SYNC Packet RX Timing
In the AX-ConfigurationUtility SYNC RX mode timing is controlled by the parameters
axradio_sync_xoscstartup
,
axradio_sync_slave_rxadvance
,
axradio_sync_slave_rxwindow
and
axradio_sync_slave_rxtimeout
. All times are
measured in periods of wtimer0, which is clocked by the low power crystal oscillator. As
shown at the top of Figure 8 the radio XTAL oscillator of the SLAVE is enabled
axradio_sync_slave_rxadvance
before the frame delimiter (SFD) of the next packet is
expected. After settling the XTAL for
axradio_sync_xoscstartup
the RX is enabled.
The RX then settles and looks for an SFD, timing out after
axradio_sync_slave_rxwindow
if no SFD is received. If an SFD is received the RX
stays on until successfully receiving a packet or until a timeout occurs after
axradio_sync_slave_rxtimeout
. (Not shown in the figure.)
Figure 8: SYNC firmware packet reception timing.
AX-ConfigurationUtility computes
axradio_sync_slave_rxadvance
and
axradio_sync_slave_rxwindow
based on the
rx_margin
which can be configured in
the SYNC Timing panel as shown at the bottom of Figure 8. The goal is to have the RX
ready
rx_margin
before the expected start of the packet. (Ready means that the
synthesizer and the analog baseband are settled. AGC settling and bit synchronization
can be done only if preamble signal is present.) The SFD timeout is set
rx_margin
after
the expected SFD. Three instances of
axradio_sync_slave_rxadvance
and
axradio_sync_slave_rxwindow
are computed. The first instance contains the
increased
rx_margin
to be used for the first packet after (re-)synchronization when the
effective packet period measurement is available yet. The second instance contains the
rx_margin
used in normal operation (“Minimum RX margin” in the SYNC Timing panel).
The third instance has
rx_margin
scaled by a factor of 4 and is used after a failed
packet reception.
Note: A processing delay occurs in the RX, i.e. the detection of the SFD is not signalled by
the RX the very moment it is on air. On the other the RX should be enabled
rx_margin
before the packet is on air. Therefore
dt_SFD
is not simply the length of preamble plus
SFD but also contains the processing delay of roughly 19 bit.