ZED-F9P-Integration Manual
UBX-18010802 - R02
4 Receiver description Page 41 of 114
Advance Information
• Optionally send UBX-MGA-INI-TIME_UTC followed by hardware time synchronization pulse if
hardware time synchronization is required.
• Send the UBX messages obtained from the AssistNow Online Service to the receiver.
4.6.4 Flow control
u-blox receivers aim to process incoming messages as quickly as possible, but there will always be
a small delay in processing each message. Uploading assistance data to the receiver can involve
sending as many as one hundred of individual messages to the receiver, one after the other. If the
communication link is fast, and/or the receiver is busy (trying to acquire new signals), it is possible
that the internal buffers will overflow and some messages will be lost. In order to combat this, u-
blox receivers support an optional flow control mechanism for assistance.
Flow control is activated by using the CFG-NAVSPG-ACKAIDING configuration item. As a result the
receiver will issue an acknowledgment message (ACK) for each assistance message it successfully
receives. The host software can examine these acknowledgments to establish whether there were
any problems with the data sent to the receiver and deduce (by the lack of acknowledgment) if any
messages have been lost. It may then be appropriate to resend some of the assistance messages.
The simplest way to implement flow control would be to send one UBX-MGA assistance message at
a time, waiting for the acknowledgment, before sending the next. However, such a strategy is likely
to introduce significant delays into the whole assistance process. The best strategy will depend on
the amount of assistance data being sent and the nature of the communications link (e.g. baud
rate of serial link). u-blox recommends that when customers are developing their host software they
start by sending all assistance messages and then analyze the resulting acknowledgments to see
if there are any loses of messages. Adding small delays during the transmission may be a simple
but effective way to avoid loss of data.
4.6.5 Authorization
The AssistNow Online Service is only available for use by u-blox customers. In order to use the
services, customers will need to obtain an authorization token from u-blox. This token must be
supplied as a parameter whenever a request is made to either service.
4.6.6 Service parameters
The information exchange with the AssistNow Online Service is based on the HTTP protocol. Upon
reception of an HTTP GET request, the server will respond with the required messages in binary
format or with an error string in text format. After delivery of all data, the server will terminate the
connection.
The HTTP GET request from the client to the server should contain a standard HTTP query string in
the request URL. The query string consists of a set of "key=value" parameters in the following form:
key=value;key=value;key=value;
The following rules apply:
• The order of keys is important
• Keys and values are case sensitive
• Keys and values must be separated by an "equal" character ("=").
• Key/value pairs must be separated by semicolons (";").
• If a value contains a list, each item in the list must be separated by a comma (",").
The following table describes the keys that are supported:
Key Name Unit/
Range
Optional Description
token String Mandatory The authorization token supplied by u-blox when a client registers to use the
service.
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