1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
|
<sect1 id="driver_nmea.c"><title><filename>nmea_parse.c</filename></title>
<informaltable frame='all' pgwide='1'>
<tgroup cols='2'>
<colspec colname='c1'></colspec>
<colspec colname='c2'></colspec>
<spanspec spanname='s1' namest='c1' nameend='c2'></spanspec>
<!-- Not documented: processGPGBS(), processOHPR(), processPASHR() -->
<thead>
<row>
<entry>Functions:-</entry><entry>Parser for NMEA strings, generic and proprietary.</entry>
</row>
</thead>
<tfoot>
<row>
<entry spanname='s1' align='left'>Notes based on code as of Mon Apr 5 21:38:06 2010 -0400.</entry>
</row>
</tfoot>
<tbody>
<row>
<entry><function>static void do_lat_lon(char *field[], struct gps_fix_t *out)</function></entry>
<entry><para>Reads a four element array containing the value and
hemisphere of the latitude and longitude of a location as text. It
converts them into signed (-ve for S and W) values. The
<structname>gps_data_t</structname> structure is updated with the
new value(s).</para></entry>
</row>
<row>
<entry><function>static void merge_ddmmyy(char *ddmmyy, struct gps_device_t *session)</function></entry>
<entry><para>If the century has not yet been stored in the nmea
driver private data, take the supplied ddmmyy date and generate and
store a ddmmyyyy date, using the century value compiled in from
<function>timebase.h</function>.</para></entry>
</row>
<row>
<entry><function>static void merge_hhmmss(char *hhmmss, struct gps_device_t *session)</function></entry>
<entry><para>Stash the present hour value before updating it from
the incoming data. If the new hour is less than the stashed value,
we have passed midnight, so update the day value. Finally update the
minutes, seconds and fractions of a second from the incoming
data.</para></entry>
</row>
<row>
<entry><function>static gps_mask_t processGPRMC(int count, char *field[], struct gps_device_t *session)</function></entry>
<entry><para>Handle a $GPRMC sentence stored in an array of strings,
one member per field.</para><para>Check if the message is stamped
valid or not.</para><para>If it is invalid, set the status and fix
mode to NO_FIX and save the corresponding flags locally; also save
the online flag to indicate we have handled a known
sentence.</para><para>If the fix is autonomous and valid, start to
decode the fields.</para><para>First, test if there are enough
fields available; then handle the date and time via
<function>merge_ddmmyy()</function> and
<function>merge_hhmmss()</function>, storing the TIME_SET flag and
storing the fix time as a UNIX-epoch relative value.</para><para>If
the sentence time and this fix time are different, we have started a
new cycle of observation, so update the sentence time and the store
the CYCLE_START_SET flag.</para><para>Whatever the number of fields,
store the fix co-ordinates via <function>do_lat_lon()</function>,
store the speed and the track and save the corresponding
flags.</para><para>Return the local aggregated flags to allow the
main copy in the session data to be updated.</para></entry>
</row>
<row>
<entry><function>static gps_mask_t processGPGLL(int count, char *field[], struct gps_device_t *session)</function></entry>
<entry><para>Preload the local flag with the ERROR_SET
flag.</para><para>Check that the sentence is usable, exiting with
the preset error flag if it is not.</para><para>If it is usable,
clear the local flags and start processing the fields, updating any
local flag fields on the way.</para><para>If the year is already
known, update the time and check for the start of cycle (see
<function>processGPRMC()</function> above).</para><para>Handle the
fix location and, if the number of received fixes is more than 8 and
the status is differential, stash the new status as STATUS_DGPS_FIX;
otherwise stash STATUS_FIX.</para><para>If the present mode is less
than 2D_FIX, update it to 2D_FIX.</para><para>Write the stashed
value of newstatus into the session status and return all the
locally aggregated flags.</para></entry>
</row>
<row>
<entry><function>static gps_mask_t processGPGGA(int c UNUSED, char *field[], struct gps_device_t *session)</function></entry>
<entry><para>Stash the last fix time. Set the status to the value in
the message and update the local flag variable.</para><para>If the
status is STATUS_NO_FIX, exit immediately, returning the locally
aggregated flags. If there is a fix, process it.</para><para>Handle
the time as in <function>processGPGLL()</function> above. Handle the
latitiude and longitude with a call to
<function>do_lat_lon()</function> above and set the local
flag.</para><para>Update the <function>satellites_used</function>
field and stash the altitude.</para><para>If the altitude is empty,
force the fix mode and status to 2D if it was 3D
previously.</para><para>If it is not empty, stash the old value of
altitude and replace it with the new value stashed earlier and set
the local flag variable. If the mode is presently less than 3D,
update it to 3D and set the local flag.</para><para>If the stashed
old altitude is NaN or the stashed fix time and current fix time are
equal, set the climb rate to 0 otherwise calculate it by dividing
the altitude difference by the time difference and set the local
flag.</para><para>If the geoid separation is available, store it,
otherwise store the value from
<function>wgs84_separation()</function> that depends on current
location.</para><para>Finally, return all the locally aggregated
flags.</para></entry>
</row>
<row>
<entry><function>static gps_mask_t processGPGSA(int count, char *field[], struct gps_device_t *session)</function></entry>
<entry><para>Start with a simple validity check on the number of
fields (for i.Trek M3) and bail out with a simple indication of
on-line status if it fails.</para><para>Set the fix mode from the
sentence and either clear the local flag variable (if an Antaris
chipset says we are in dead-reckoning mode) or set the MODE_SET
flag.</para><para>Update all the DOP fields from the sentence, clear
the count of used satellites, then scan all the satellite
data.</para><para>If any satellite is good (prn != 0), store the prn
and increment the count of used satellites.</para><para>Finally, set
the local flags to indicate that DOPs are available and return all
the locally aggregated flags.</para></entry>
</row>
<row>
<entry><function>static gps_mask_t processGPGSV(int count, char *field[], struct gps_device_t *session)</function></entry>
<entry><para>Check if the sentence has too few fields or the wrong
number fo fields. In this case, clear the data for all satellites
and return with an error indication.</para><para>Start to parse the
sentence. First, note how many sentences are to be expected to
complete the data transfer.</para><para>If the sentence number is
invalid, clear the data for all satellites and return with an error
indication.</para><para>If this is the first sentence of the
sequence, clear the data for all satellites.</para><para>Loop
through the sentence fields, updating the session's satellite
data.</para><para>If any satellite number is higher than the number
of channels, clear all satellite data and break out of the
loop.</para><para>Assuming this is not a buggy chipset
(e.g. Motorola Oncore GT+), update the satellite count and loop
again.</para><para>If this was the last sentence of the block and
the number of satellites seen is not the same as the number
reported, generate an error log.</para><para>If this is not the last
sentence of the block, exit early and return an error flag as a
guard.</para><para>Finally, on the last sentence, carry out a sanity
check and either return an error flag or a SATELLITE_SET
flag.</para></entry>
</row>
<row>
<entry><function>static gps_mask_t processPGRME(int c UNUSED, char *field[], struct gps_device_t *session)</function></entry>
<entry><para>Check that the error estimate data is good. If not, set
all error estimate fields to 100m and return an error
flag.</para><para>If they are good, calculate the error value and
store it. Return the appropriate flag values.</para></entry>
</row>
<row>
<entry><function>static gps_mask_t processGPZDA(int c UNUSED, char *field[], struct gps_device_t *session)</function></entry>
<entry><para>Set the local flag variable to indicate that the time
is available.</para><para>Store the actual time by a call to
<function>merge_hhmmss()</function> and fill in the other fields
from the sentence data.</para><para>If the sentence is not
timestamped the same as the fixtime, set the CYCLE_START_SET
flag.</para><para>Update the fixtime to the sentence
timestamp.</para><para>Finally, return all the locally aggregated
flags.</para></entry>
</row>
<row>
<entry><function>static gps_mask_t processTNTHTM(int c UNUSED, char *field[], struct gps_device_t *session)</function></entry>
<entry><para>Set the local variable to indicate the unit is
on-line.</para><para>Fill all appropriate fields from the sentence
and set the associated flags in the local flag
variable.</para><para>Set the fix status and return all the locally
aggregated flags.</para></entry>
</row>
<row>
<entry><function>static short nmea_checksum(char *sentence, unsigned char *correct_sum)</function></entry>
<entry><para>Calculate and return the checksum of an NMEA sentence.</para></entry>
</row>
<row>
<entry><function>gps_mask_t nmea_parse(char *sentence, struct gps_device_t *session)</function></entry>
<entry><para>Test that the length of the NMEA sentence is
acceptable, simply returning an on-line indication if it is too long
to handle.</para><para>If it is within limits, make a local copy and
split it on the commas into an array, one field per
element.</para><para>Use the first element to match the command to
the table of decodable commands.</para><para>Check if it is
supported and the number of fields is reasonable, invoke the correct
decoder and return the value from that call.</para><para>If it fails
the check, simply return an on-line status.</para><para>This function is
also responsible for performing adaptive end-of-cycle
detection.</para></entry>
</row>
<row>
<entry><function>void nmea_add_checksum(char *sentence)</function></entry>
<entry><para>Calculate the checksum then append '*' + the checksum + CR/LF to the end of an NMEA sentence, skipping any existing '*'.</para></entry>
</row>
<row>
<entry><function>int nmea_write(struct gps_device_t *session, const char *fmt, ... )</function></entry>
<entry><para>Ship a string to an NMEA device, adding a checksum and
CR/LF if needed. A checksum is added only if the sentence begins
with '$'. Bytes written are returned.</para></entry>
</row>
<row>
<entry><function>int nmea_send(struct gps_device_t *session, , const char *fmt, ... )</function></entry>
<entry><para>A wrapper around <function>nmea_write()</function> to
give it sprintf-like varargs behavior.</para></entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect1>
|
