DW1000 User Manual
© Decawave Ltd 2017
Version 2.12
Page 27 of 242
to minimise this the host microprocessor may sometimes be late invoking the delayed TX, i.e. so that the
system clock has passed the specified start time (i.e.
internal start time
mentioned above) and then the IC
has to complete almost a whole clock count period before the start time is reached. The HPDWARN event
status flag in
Register file: 0x0F – System Event Status Register
warns of this “lateness” condition so that
during application development the delay may be chosen large enough to generally avoid this lateness. The
HPDWARN status flag also serves to facilitate detection of this late invocation condition so that recovery
measures may be taken should it ever occur in deployed product. For delayed transmission it is the
internal
start time
mentioned above that is used when deciding whether to set the HPDWARN event for the delayed
transmit. As long as the preamble start time is the near future, the HPDWARN event flag will not be set. If a
long delay was intended then the HPDWARN flag can be ignored and the transmission will begin at the
allotted time. If a long delay was not intended then the transmission can be stopped by issuing a TRXOFF via
Register file: 0x0D – System Control Register
Under normal circumstances the IC transmitter needs a few microseconds to power up the transmitter – this
time is correctly handled for the RMARKER positioning, but is not included in the HPDWARN calculation. So,
if the initiation of a delayed transmission is commanded early enough so that it does not generate a
HPDWARN event but not sufficiently early for the IC transmitter to power up before the start of preamble;
then frame transmission will still occur and the RMARKER will be sent at the correct time, but, during the
initial few symbols of preamble (while the transmitter is powering-up) the preamble may not be sent
correctly. For most use cases this will not be an issue, as there is generally ample preamble remaining for
good reception. However for shorter preamble sequences, especially the 64-symbol preamble sequence,
losing a few symbols can have a performance impact.
When using delayed transmission with 64-symbol preambles then, designers should also be aware that the
power-up time for the transmitter is not included in the HPDWARN calculation which means that if the
preamble start time is too close then the initial few symbols of preamble (while the transmitter is powering-
up) may not be sent correctly. This is flagged in a transient TXPUTE bit status and counted in
0x2F:1A – Transmitter Power-Up Warning Counter
, (assuming counting is enabled by the EVC_EN bit in
Register 0x2F:00 – Event Counter Control
). It is recommended that checks are added, during design
validation, to ensure that the HPDWARN event does not happen and also (especially for short preambles)
that the TXPUTE event does not happen, and take appropriate measures to avoid them (like increasing the
response delay time).
3.4 Extended Length Data Frames
Standard IEEE 802.15.4-2011 UWB frames carry up to 127 bytes of payload. The DW1000 supports a non-
standard mode of operation with frame lengths up to 1023 bytes of data. This mode of operation is enabled
via the PHR_MODE selection bits of
Register file: 0x04 – System Configuration
In this proprietary mode the PHY header (PHR) is redefined to carry the 3 extra bits of frame length. In order
to communicate extended length data frames between two DW1000 devices both ends must be set to the
long frame PHY header mode via the PHR_MODE selection bits of
Register file: 0x04 – System Configuration
If the setting is only at one end of a link any attempt at communication will fail with PHR errors being
reported. When long frame mode is selected, the DW1000 will be unable to communicate with any device
