Technical Manual

45
The Radio Interface Task
As long as another frame will follow in this time interval addressed to a station that
is known to be also active, the header sent to that station will be a short one.
4.5.4. Data Frames
The data frames are the blocks of data extracted from the radio frames, after the CRC
and other information (source address) was checked. The data frame as well as its
length are passed to the upper layers of the software.
Figure 27. Generic Data Frame structure.
A data frame is composed of two main parts: a header, containing the frame type as
well as the routing information, and a data block. The length of the data block can be
easily computed by subtracting the header length (HLEN + 1 for the TYPE) from the
original data frame length received from the lower layer of software (the radio frame
length). Additional explanations on the notation used in the diagram:
TYPE is the type of frame; the types recognized and/or used by the A720 will
be detailed individually later in this chapter.
HLEN is the header length: it represents the number of bytes used to describe
the route the frame will go (or went). The maximum number of hops is 8, that
is, 8 intermediate stations plus source and destination. Each station is de-
scribed by its unique 16-bit address.
SRC, HOP and DEST, are the source, the hops and the destination addresses.
While the hops may be missing (no routing stations between source and des-
tination), the source and destination are mandatory.
DATA is the data proper field. It is limited in length, its maximum size being
dependent also on the particular route: if the route is longer (8 hops) then the
data block is limited to 48 bytes. Depending on the frame type, the data block
may be inexistent (zero length).
4.5.5. Frame Types
Although the original Adcon Radio Protocol contains many frame types, only those
relevant (recognized and /or used) to the A720 will be presented here.
4.5.5.1. Request
ID 1
FORMAT struct {
time_t init_time;
time_t req_time;
TYPE HLEN SRC-H
SRC-L
.......
HOP1-H HOP1-L HOPn-H HOPn-L DEST-LDEST-H DATA1 DATA2 DATAn
.......
Header (Frame Type + Routing Information) Data