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AP_Filesystem: document extra restrictions in param.pck

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Andrew Tridgell 2020-04-30 21:15:28 +10:00
parent 685d0666e9
commit f0fb64005d
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libraries/AP_Filesystem/README.md
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@ -19,6 +19,16 @@ The VFS interfaces that don't represent local filesystem objects on
the flight controller are prefixed with an '@' symbol. Currently there the flight controller are prefixed with an '@' symbol. Currently there
are two interfaces, the @PARAM interface and the @SYS interface. are two interfaces, the @PARAM interface and the @SYS interface.
### FTP Protocol Extension
To facilitate more efficient file transfer over commonly used SiK
radios I have added an extension to the ftp burst protocol where the
'size' field in the burst read request sets the block size of the
burst replies. This helps as SiK radios do badly with very large
packets. I have found that the best results with SiK radios is
achieved with a burst read size of 110. If the size field is set to
zero then the default of the max size (239) is used.
## The @PARAM VFS ## The @PARAM VFS
The @PARAM VFS allows a GCS to very efficiently download full or The @PARAM VFS allows a GCS to very efficiently download full or
@ -28,6 +38,13 @@ which is a packed representation of the full parameter
list. Downloading the full parameter list via this interface is a lot list. Downloading the full parameter list via this interface is a lot
faster than using the traditional mavlink parameter messages. faster than using the traditional mavlink parameter messages.
The @PARAM/param.pck file has a special restriction that all reads
from the file on a single file handle must be of the same size. This
allows the server to ensure that filling in of lost transfers cannot
cause a parameter value to be split across a network block, which
prevents corruption. Attempts to vary the read size after the first
read will return a failed read.
The file format of the @PARAM/param.pck file is as follows The file format of the @PARAM/param.pck file is as follows
### File header ### File header