ZED-F9K - Integration manual
• Optionally send UBX-MGA-INI-TIME_UTC followed by hardware time synchronization pulse.
• Send the UBX messages obtained from the AssistNow Online Service to the receiver.
3.7.4.3 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 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 setting the CFG-NAVSPG-ACKAIDING configuration item. As a result
the receiver will issue an acknowledgment message (UBX-MGA-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 necessary to resend some of the
assistance messages.
The simplest way to implement flow control would be to send one UBX-MGA 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 depends 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 any
messages have been lost. Adding small delays during the transmission may be a simple but effective
way to avoid loss of data.
3.7.4.4 Service parameters
The information exchange with the AssistNow Online Service is based on the HTTP protocol. The
u-blox MGA service supports encrypted HTTPS communication. 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.
gnss
String
Mandatory A comma-separated list of the GNSS for which data should be returned. Valid GNSS
are: gps, gal, glo, bds and qzss (case-sensitive).
UBX-20046189 - R01
3 Receiver functionality
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C1-Public
Early production information
