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modes_reader.c
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modes_reader.c
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/*
* Part of mlat-client - an ADS-B multilateration client.
* Copyright 2015, Oliver Jowett <[email protected]>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "_modes.h"
/* decoder modes */
typedef enum {
DECODER_NONE, /* Not configured */
DECODER_BEAST, /* Beast binary, freerunning 48-bit timestamp @ 12MHz */
DECODER_RADARCAPE, /* Beast binary, 1GHz Radarcape timestamp, UTC synchronized from GPS */
DECODER_RADARCAPE_EMULATED, /* Beast binary, 1GHz Radarcape timestamp, not synchronized */
DECODER_AVR, /* AVR, no timestamp */
DECODER_AVRMLAT, /* AVR, freerunning 48-bit timestamp @ 12MHz */
DECODER_SBS, /* Kinetic SBS, freerunning 20MHz 24-bit timestamp, wraps around all the time but we try to widen it */
} decoder_mode;
/* A timestamp that indicates the data is synthetic, created from a
* multilateration result. (FF 00 "MLAT")
*/
#define MAGIC_MLAT_TIMESTAMP 0xFF004D4C4154ULL
/* a modesreader object */
typedef struct {
PyObject_HEAD
/* decoder characteristics */
decoder_mode decoder_mode;
const char *decoder_mode_string;
unsigned long long frequency;
const char *epoch;
unsigned long long last_timestamp; /* last seen timestamp */
unsigned int radarcape_utc_bugfix;
/* configurable bits */
char allow_mode_change;
char want_zero_timestamps;
char want_mlat_messages;
char want_invalid_messages;
char want_events;
/* filtering */
PyObject *seen;
PyObject *default_filter;
PyObject *specific_filter;
PyObject *modeac_filter;
/* stats */
unsigned int received_messages;
unsigned int suppressed_messages;
} modesreader;
/* methods for the modesreader type */
static PyObject *modesreader_new(PyTypeObject *type, PyObject *args, PyObject *kwds);
static int modesreader_init(modesreader *self, PyObject *args, PyObject *kwds);
static void modesreader_dealloc(modesreader *self);
static int modesreader_setmode(modesreader *self, PyObject *mode, void *dummy);
static PyObject *modesreader_getmode(modesreader *self, void *dummy);
static PyObject *modesreader_feed(modesreader *self, PyObject *args, PyObject *kwds);
/* modesreader fields */
static PyMemberDef modesreaderMembers[] = {
/* these two are derived from the current mode always */
{ "frequency", T_ULONGLONG, offsetof(modesreader, frequency), READONLY, "timestamp frequency" },
{ "epoch", T_STRING, offsetof(modesreader, epoch), READONLY, "timestamp epoch" },
{ "last_timestamp", T_ULONGLONG, offsetof(modesreader, last_timestamp), 0, "last timestamp seen" },
{ "allow_mode_change", T_BOOL, offsetof(modesreader, allow_mode_change), 0, "can the decoder change mode based on status messages it receives?" },
{ "want_zero_timestamps", T_BOOL, offsetof(modesreader, want_zero_timestamps), 0, "should the decoder return messages with zero timestamps?" },
{ "want_mlat_messages", T_BOOL, offsetof(modesreader, want_mlat_messages), 0, "should the decoder return synthetic mlat messages?" },
{ "want_invalid_messages", T_BOOL, offsetof(modesreader, want_invalid_messages), 0, "should the decoder return invalid messages?" },
{ "want_events", T_BOOL, offsetof(modesreader, want_events), 0, "should the decoder return metadata events?" },
{ "seen", T_OBJECT, offsetof(modesreader, seen), 0, "set of addresses seen by the decoder" },
{ "default_filter", T_OBJECT, offsetof(modesreader, default_filter), 0, "DF accept filter for all aircraft"},
{ "specific_filter", T_OBJECT, offsetof(modesreader, specific_filter), 0, "DF accept filter for specific aircraft"},
{ "modeac_filter", T_OBJECT, offsetof(modesreader, modeac_filter), 0, "Mode A/C accept filter"},
{ "received_messages", T_UINT, offsetof(modesreader, received_messages), 0, "total number of messages decoded"},
{ "suppressed_messages", T_UINT, offsetof(modesreader, suppressed_messages), 0, "number of messages suppressed by filtering"},
{ NULL, 0, 0, 0, NULL }
};
/* .. and the mode field which has a special getter/setter */
static PyGetSetDef modesreaderGetSet[] = {
{ "mode", (getter)modesreader_getmode, (setter)modesreader_setmode, "decoder mode", NULL },
{ NULL, NULL, NULL, NULL, NULL }
};
/* modesreader methods */
static PyMethodDef modesreaderMethods[] = {
{ "feed", (PyCFunction)modesreader_feed, METH_VARARGS|METH_KEYWORDS, "Process and decode some data." },
{ NULL, NULL, 0, NULL }
};
/* modesreader type definition */
static PyTypeObject modesreaderType = {
PyVarObject_HEAD_INIT(NULL, 0)
"_modes.Reader", /* tp_name */
sizeof(modesreader), /* tp_basicsize */
0, /* tp_itemsize */
(destructor)modesreader_dealloc, /* tp_dealloc */
0, /* tp_print */
0, /* tp_getattr */
0, /* tp_setattr */
0, /* tp_reserved */
0, /* tp_repr */
0, /* tp_as_number */
0, /* tp_as_sequence */
0, /* tp_as_mapping */
0, /* tp_hash */
0, /* tp_call */
0, /* tp_str */
PyObject_GenericGetAttr, /* tp_getattro */
PyObject_GenericSetAttr, /* tp_setattro */
0, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT|Py_TPFLAGS_BASETYPE, /* tp_flags */
"A ModeS stream reader.", /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */
0, /* tp_richcompare */
0, /* tp_weaklistoffset */
0, /* tp_iter */
0, /* tp_iternext */
modesreaderMethods, /* tp_methods */
modesreaderMembers, /* tp_members */
modesreaderGetSet, /* tp_getset */
0, /* tp_base */
0, /* tp_dict */
0, /* tp_descr_get */
0, /* tp_descr_set */
0, /* tp_dictoffset */
(initproc)modesreader_init, /* tp_init */
0, /* tp_alloc */
modesreader_new, /* tp_new */
};
/* lookup table for decoder_mode <-> python strings */
static struct {
decoder_mode mode;
const char *cstr;
PyObject *pystr;
} modetable[] = {
{ DECODER_BEAST, "BEAST", NULL },
{ DECODER_RADARCAPE, "RADARCAPE", NULL },
{ DECODER_RADARCAPE_EMULATED, "RADARCAPE_EMULATED", NULL },
{ DECODER_AVR, "AVR", NULL },
{ DECODER_AVRMLAT, "AVRMLAT", NULL },
{ DECODER_SBS, "SBS", NULL },
{ DECODER_NONE, NULL, NULL }
};
/* internal helpers */
static PyObject *feed_beast(modesreader *self, Py_buffer *buf, int max_messages);
static PyObject *feed_avr(modesreader *self, Py_buffer *buf, int max_messages);
static PyObject *feed_sbs(modesreader *self, Py_buffer *buf, int max_messages);
static void set_decoder_mode(modesreader *self, decoder_mode newmode);
static PyObject *radarcape_settings_to_list(uint8_t settings);
static PyObject *radarcape_status_to_dict(uint8_t *message);
static int filter_message(modesreader *self, PyObject *message);
/*
* module setup/teardown
*/
int modesreader_module_init(PyObject *m)
{
int i;
if (PyType_Ready(&modesreaderType) < 0)
goto error;
for (i = 0; modetable[i].cstr != NULL; ++i) {
PyObject *pystr = PyUnicode_FromString(modetable[i].cstr);
if (pystr == NULL) {
goto error;
}
Py_INCREF(pystr);
modetable[i].pystr = pystr;
if (PyModule_AddObject(m, modetable[i].cstr, pystr) < 0)
goto error;
}
Py_INCREF(&modesreaderType);
if (PyModule_AddObject(m, "Reader", (PyObject *)&modesreaderType) < 0) {
Py_DECREF(&modesreaderType);
goto error;
}
return 0;
error:
for (i = 0; modetable[i].cstr != NULL; ++i) {
Py_CLEAR(modetable[i].pystr);
}
return -1;
}
void modesreader_module_free(PyObject *m)
{
int i;
for (i = 0; modetable[i].cstr != NULL; ++i) {
Py_CLEAR(modetable[i].pystr);
}
}
static PyObject *modesreader_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
modesreader *self;
self = (modesreader *)type->tp_alloc(type, 0);
if (self == NULL)
return NULL;
/* minimal init */
set_decoder_mode(self, DECODER_NONE);
self->last_timestamp = 0;
self->allow_mode_change = 1;
self->want_zero_timestamps = 0;
self->want_mlat_messages = 0;
self->want_invalid_messages = 0;
self->want_events = 1;
Py_INCREF(Py_None); self->seen = Py_None;
Py_INCREF(Py_None); self->default_filter = Py_None;
Py_INCREF(Py_None); self->specific_filter = Py_None;
Py_INCREF(Py_None); self->modeac_filter = Py_None;
self->received_messages = self->suppressed_messages = 0;
return (PyObject *)self;
}
static void modesreader_dealloc(modesreader *self)
{
Py_CLEAR(self->seen);
Py_CLEAR(self->default_filter);
Py_CLEAR(self->specific_filter);
Py_CLEAR(self->modeac_filter);
Py_TYPE(self)->tp_free((PyObject*)self);
}
static int modesreader_init(modesreader *self, PyObject *args, PyObject *kwds)
{
static char *kwlist[] = { "mode", NULL };
PyObject *mode = Py_None;
if (!PyArg_ParseTupleAndKeywords(args, kwds, "|O", kwlist, &mode))
return -1;
if (modesreader_setmode(self, mode, NULL) < 0)
return -1;
return 0;
}
static int modesreader_setmode(modesreader *self, PyObject *mode, void *dummy)
{
int i;
if (mode == Py_None) {
set_decoder_mode(self, DECODER_NONE);
return 0;
}
for (i = 0; modetable[i].cstr != NULL; ++i) {
int res = PyObject_RichCompareBool(modetable[i].pystr, mode, Py_EQ);
if (res < 0)
return -1;
if (res == 1) {
set_decoder_mode(self, modetable[i].mode);
break;
}
}
if (modetable[i].cstr == NULL) {
PyErr_SetString(PyExc_ValueError, "unrecognized decoder mode");
return -1;
}
return 0;
}
static PyObject *modesreader_getmode(modesreader *self, void *dummy)
{
int i;
for (i = 0; modetable[i].cstr; ++i) {
if (self->decoder_mode == modetable[i].mode) {
Py_INCREF(modetable[i].pystr);
return modetable[i].pystr;
}
}
Py_INCREF(Py_None);
return Py_None;
}
/* feed some data to the reader and does one of:
* 1) returns a tuple (bytes_consumed, messages, error_pending), or
* 2) throws an exception
*
* If a stream error is seen, but some messages were parsed OK,
* then an exception is not immediately thrown and the parsed
* messages are returned with error_pending = True. The caller
* should call feed again (after consuming the given number of
* bytes) to get the exception.
*
* Internal errors (e.g. out of memory) are thrown immediately.
*/
static PyObject *modesreader_feed(modesreader *self, PyObject *args, PyObject *kwds)
{
Py_buffer buffer;
PyObject *rv = NULL;
int max_messages = 0;
static char *kwlist[] = { "buffer", "max_messages", NULL };
if (!PyArg_ParseTupleAndKeywords(args, kwds, "y*|i", kwlist, &buffer, &max_messages))
return NULL;
if (buffer.itemsize != 1) {
PyErr_SetString(PyExc_ValueError, "buffer itemsize is not 1");
goto out;
}
if (!PyBuffer_IsContiguous(&buffer, 'C')) {
PyErr_SetString(PyExc_ValueError, "buffer is not contiguous");
goto out;
}
switch (self->decoder_mode) {
case DECODER_NONE:
PyErr_SetString(PyExc_NotImplementedError, "decoder mode is None, no decoder type selected");
break;
case DECODER_BEAST:
case DECODER_RADARCAPE:
case DECODER_RADARCAPE_EMULATED:
rv = feed_beast(self, &buffer, max_messages);
break;
case DECODER_AVR:
case DECODER_AVRMLAT:
rv = feed_avr(self, &buffer, max_messages);
break;
case DECODER_SBS:
rv = feed_sbs(self, &buffer, max_messages);
break;
default:
PyErr_Format(PyExc_AssertionError, "decoder somehow got into illegal mode %d", (int)self->decoder_mode);
break;
}
out:
PyBuffer_Release(&buffer);
return rv;
}
static void set_decoder_mode(modesreader *self, decoder_mode newmode)
{
self->decoder_mode = newmode;
switch (newmode) {
case DECODER_BEAST:
self->frequency = 12000000ULL; /* assumed */
self->epoch = NULL;
break;
case DECODER_RADARCAPE:
self->frequency = 1000000000ULL;
self->epoch = "utc_midnight";
break;
case DECODER_RADARCAPE_EMULATED:
self->frequency = 1000000000ULL;
self->epoch = NULL;
break;
case DECODER_AVRMLAT:
self->frequency = 12000000ULL; /* assumed */
self->epoch = NULL;
break;
case DECODER_SBS:
self->frequency = 20000000ULL;
self->epoch = NULL;
break;
case DECODER_AVR:
default:
self->frequency = 0;
self->epoch = NULL;
break;
}
}
/* turn a radarcape DIP switch setting byte into a Python list of settings strings */
static PyObject *radarcape_settings_to_list(uint8_t settings)
{
return Py_BuildValue("[s,s,s,s,s,s,s]",
settings & 0x01 ? "beast" : (settings & 0x04 ? "avrmlat" : "avr"),
settings & 0x02 ? "filtered_frames" : "all_frames",
settings & 0x08 ? "no_crc" : "check_crc",
settings & 0x10 ? "gps_timestamps" : "legacy_timestamps",
settings & 0x20 ? "rtscts" : "no_rtscts",
settings & 0x40 ? "no_fec" : "fec",
settings & 0x80 ? "modeac" : "no_modeac");
}
/* turn a radarcape GPS status byte into a Python dict */
static PyObject *radarcape_gpsstatus_to_dict(uint8_t status)
{
if (!(status & 0x80)) {
return Py_BuildValue("{s:O,s:O}",
"utc_bugfix", Py_False,
"timestamp_ok", Py_True
);
}
return Py_BuildValue("{s:O,s:O,s:O,s:O,s:O,s:O,s:O}",
"utc_bugfix", Py_True,
"timestamp_ok", (status & 0x20 ? Py_False : Py_True),
"sync_ok", (status & 0x10 ? Py_True : Py_False),
"utc_offset_ok", (status & 0x08 ? Py_True : Py_False),
"sats_ok", (status & 0x04 ? Py_True : Py_False),
"tracking_ok", (status & 0x02 ? Py_True : Py_False),
"antenna_ok", (status & 0x01 ? Py_True : Py_False));
}
/* turn a radarcape 0x34 status message into a Python dict */
static PyObject *radarcape_status_to_dict(uint8_t *message)
{
return Py_BuildValue("{s:N,s:i,s:N}",
"settings", radarcape_settings_to_list(message[0]),
"timestamp_pps_delta", (int)(int8_t)message[1],
"gps_status", radarcape_gpsstatus_to_dict(message[2]));
}
/* create an event message for a timestamp jump */
static PyObject *make_timestamp_jump_event(modesreader *self, unsigned long long timestamp)
{
PyObject *eventdata = Py_BuildValue("{s:K}",
"last-timestamp", self->last_timestamp);
if (eventdata == NULL)
return NULL;
return modesmessage_new_eventmessage(DF_EVENT_TIMESTAMP_JUMP, timestamp, eventdata);
}
/* create an event message for a decoder mode change. the new mode should already be set. */
static PyObject *make_mode_change_event(modesreader *self)
{
PyObject *eventdata = Py_BuildValue("{s:N,s:K,s:s}",
"mode", modesreader_getmode(self, NULL),
"frequency", self->frequency,
"epoch", self->epoch);
if (eventdata == NULL)
return NULL;
return modesmessage_new_eventmessage(DF_EVENT_MODE_CHANGE, 0, eventdata);
}
/* create an event message for an epoch rollover (e.g. GPS end of day) */
static PyObject *make_epoch_rollover_event(modesreader *self, unsigned long long timestamp)
{
PyObject *eventdata = PyDict_New();
if (eventdata == NULL)
return NULL;
return modesmessage_new_eventmessage(DF_EVENT_EPOCH_ROLLOVER, timestamp, eventdata);
}
/* create an event message for a radarcape status report */
static PyObject *make_radarcape_status_event(modesreader *self, unsigned long long timestamp, uint8_t *data)
{
PyObject *eventdata = radarcape_status_to_dict(data);
if (eventdata == NULL)
return NULL;
return modesmessage_new_eventmessage(DF_EVENT_RADARCAPE_STATUS, timestamp, eventdata);
}
/* create an event message for a radarcape position report */
static PyObject *radarcape_position_to_dict(uint8_t *data)
{
float lat, lon, alt;
lat = _PyFloat_Unpack4(data + 4, 1);
if (lat == -1.0 && PyErr_Occurred())
return NULL;
lon = _PyFloat_Unpack4(data + 8, 1);
if (lon == -1.0 && PyErr_Occurred())
return NULL;
alt = _PyFloat_Unpack4(data + 12, 1);
if (alt == -1.0 && PyErr_Occurred())
return NULL;
return Py_BuildValue("{s:f,s:f,s:f}",
"lat", lat,
"lon", lon,
"alt", alt);
}
static PyObject *make_radarcape_position_event(modesreader *self, uint8_t *data)
{
PyObject *eventdata = radarcape_position_to_dict(data);
if (eventdata == NULL)
return NULL;
return modesmessage_new_eventmessage(DF_EVENT_RADARCAPE_POSITION, 0, eventdata);
}
static int is_synthetic_timestamp(unsigned long long timestamp)
{
return (timestamp == 0 || timestamp == MAGIC_MLAT_TIMESTAMP);
}
/* check if the given timestamp is in range (not a jump), return 1 if it is */
static int timestamp_check(modesreader *self, unsigned long long timestamp)
{
if (is_synthetic_timestamp(timestamp))
return 1;
if (self->last_timestamp == 0)
return 1;
if (self->frequency == 0)
return 1;
if (self->last_timestamp > timestamp && (self->last_timestamp - timestamp) > 90 * self->frequency)
return 0;
if (self->last_timestamp < timestamp && (timestamp - self->last_timestamp) > 90 * self->frequency)
return 0;
return 1;
}
/* update self->last_timestamp given that we just saw this timestamp */
static void timestamp_update(modesreader *self, unsigned long long timestamp)
{
if (is_synthetic_timestamp(timestamp)) {
/* special timestamps, don't use them */
return;
}
if (self->last_timestamp == 0 || self->frequency == 0) {
/* startup cases, just accept whatever */
self->last_timestamp = timestamp;
return;
}
if (self->last_timestamp > timestamp && (self->last_timestamp - timestamp) < 90 * self->frequency) {
/* ignore small moves backwards */
return;
}
if ((self->decoder_mode == DECODER_RADARCAPE || self->decoder_mode == DECODER_RADARCAPE_EMULATED) &&
timestamp >= (86340 * 1000000000ULL) && self->last_timestamp <= (60 * 1000000000ULL)) {
/* in radarcape mode, don't allow last_timestamp to roll back to the previous day
* as we will have already issued an epoch reset
*/
return;
}
self->last_timestamp = timestamp;
}
/* feed implementation for Beast-format data (including Radarcape) */
static PyObject *feed_beast(modesreader *self, Py_buffer *buffer, int max_messages)
{
PyObject *rv = NULL;
uint8_t *buffer_start, *p, *eod;
int message_count = 0;
PyObject *message_tuple = NULL;
PyObject **messages = NULL;
int error_pending = 0;
buffer_start = buffer->buf;
if (max_messages <= 0) {
/* allocate the maximum size we might need, given a minimal encoding of:
* <1A> <'1'> <6 bytes timestamp> <1 byte signal> <2 bytes message> = 11 bytes total
*/
max_messages = buffer->len / 11 + 2;
}
messages = calloc(max_messages, sizeof(PyObject*));
if (!messages) {
PyErr_NoMemory();
goto out;
}
/* parse messages */
p = buffer_start;
eod = buffer_start + buffer->len;
while (p+2 <= eod && message_count+2 < max_messages) {
int message_len = -1;
uint64_t timestamp;
uint8_t signal;
uint8_t data[14];
uint8_t *m, *eom;
int i;
uint8_t type;
PyObject *message;
int wanted;
int has_timestamp_signal;
if (p[0] != 0x1a) {
error_pending = 1;
if (message_count > 0)
goto nomoredata;
PyErr_Format(PyExc_ValueError, "Lost sync with input stream: expected a 0x1A marker at offset %d but found 0x%02x instead", (int) (p - buffer_start), (int)p[0]);
goto out;
}
has_timestamp_signal = 1;
type = p[1];
switch (type) {
case '1': message_len = 2; break; /* mode A/C */
case '2': message_len = 7; break; /* mode S short */
case '3': message_len = 14; break; /* mode S long */
case '4': message_len = 14; break; /* radarcape status message */
case '5':
/* radarcape position message, no timestamp/signal bytes */
message_len = 21;
has_timestamp_signal = 0;
break;
default:
error_pending = 1;
if (message_count > 0)
goto nomoredata;
PyErr_Format(PyExc_ValueError, "Lost sync with input stream: unexpected message type 0x%02x after 0x1A marker at offset %d", (int)p[1], (int) (p - buffer_start));
goto out;
}
m = p + 2;
eom = m + message_len + (has_timestamp_signal ? 7 : 0);
if (eom > eod)
break;
#define ADVANCE \
do { \
if (*m++ == 0x1a) { \
if (m < eod && *m != 0x1a) { \
error_pending = 1; \
if (message_count > 0) \
goto nomoredata; \
PyErr_SetString(PyExc_ValueError, "Lost sync with input stream: expected 0x1A after 0x1A escape"); \
goto out; \
} \
++m, ++eom; \
if (eom > eod) \
goto nomoredata; \
} \
} while(0)
if (has_timestamp_signal) {
/* timestamp, 6 bytes */
timestamp = *m;
ADVANCE;
timestamp = (timestamp << 8) | *m;
ADVANCE;
timestamp = (timestamp << 8) | *m;
ADVANCE;
timestamp = (timestamp << 8) | *m;
ADVANCE;
timestamp = (timestamp << 8) | *m;
ADVANCE;
timestamp = (timestamp << 8) | *m;
ADVANCE;
/* signal, 1 byte */
signal = *m;
ADVANCE;
} else {
timestamp = 0;
signal = 0;
}
/* message, N bytes */
for (i = 0; i < message_len; ++i) {
data[i] = *m;
ADVANCE;
}
/* do some filtering */
if (type == '4') {
/* radarcape-style status message, use this to switch our decoder type */
self->radarcape_utc_bugfix = (data[2] & 0x80) == 0x80;
if (self->allow_mode_change) {
decoder_mode newmode;
if (data[0] & 0x10) {
/* radarcape in GPS timestamp mode */
if ((data[2] & 0x20) == 0x20) {
newmode = DECODER_RADARCAPE_EMULATED;
} else {
newmode = DECODER_RADARCAPE;
}
} else {
/* radarcape in 12MHz timestamp mode */
newmode = DECODER_BEAST;
}
/* handle mode changes by inserting an event message */
if (newmode != self->decoder_mode) {
set_decoder_mode(self, newmode);
if (self->want_events) {
if (! (messages[message_count++] = make_mode_change_event(self)))
goto out;
}
}
}
}
if (has_timestamp_signal && !is_synthetic_timestamp(timestamp)) {
if (self->decoder_mode == DECODER_BEAST) {
/* 12MHz mode */
/* check for very out of range value
* (dump1090 can hold messages for up to 60 seconds! so be conservative here)
* also work around dump1090-mutability issue #47 which can send very stale Mode A/C messages
*/
if (self->want_events && type != '1' && !timestamp_check(self, timestamp)) {
if (! (messages[message_count++] = make_timestamp_jump_event(self, timestamp)))
goto out;
}
/* adjust the timestamps so they always reflect the start of the frame */
uint64_t adjust;
if (type == '1') {
// Mode A/C, timestamp reported at F2 which is 20.3us after F1
// this is 243.6 cycles at 12MHz
adjust = 244;
} else if (type == '2') {
// Mode S short, timestamp reported at end of frame, frame is 8us preamble plus 56us data
// this is 768 cycles at 12MHz
adjust = 768;
} else if (type == '3') {
// Mode S long, timestamp reported halfway through the frame (at bit 56), same offset as Mode S short
adjust = 768;
} else {
// anything else we assume is already correct
adjust = 0;
}
if (timestamp < adjust) {
timestamp = 0;
} else {
timestamp = timestamp - adjust;
}
} else {
/* gps mode */
/* adjust timestamp so that it is a contiguous nanoseconds-since-
* midnight value, rather than the raw form which skips values once
* a second
*/
uint64_t nanos = timestamp & 0x00003FFFFFFF;
uint64_t secs = timestamp >> 30;
if (!self->radarcape_utc_bugfix) {
/* fix up the timestamp so it is UTC, not 1 second ahead */
if (secs == 0) {
secs = 86399;
} else {
--secs;
}
}
timestamp = nanos + secs * 1000000000;
/* adjust the timestamps so they always reflect the start of the frame */
uint64_t adjust;
if (type == '1') {
// Mode A/C, timestamp reported at F2 which is 20.3us after F1
adjust = 20300;
} else if (type == '2') {
// Mode S short, timestamp reported at end of frame, frame is 8us preamble plus 56us data
adjust = 64000;
} else if (type == '3') {
// Mode S long, timestamp reported at end of frame, frame is 8us preamble plus 112us data
adjust = 120000;
} else {
// anything else we assume is already correct
adjust = 0;
}
if (adjust <= timestamp) {
timestamp = timestamp - adjust;
} else {
/* wrap it to the previous day */
timestamp = timestamp + 86400 * 1000000000ULL - adjust;
}
/* check for end of day rollover */
if (self->want_events && self->last_timestamp >= (86340 * 1000000000ULL) && timestamp <= (60 * 1000000000ULL)) {
if (! (messages[message_count++] = make_epoch_rollover_event(self, timestamp)))
goto out;
} else if (self->want_events && type != '1' && !timestamp_check(self, timestamp)) {
if (! (messages[message_count++] = make_timestamp_jump_event(self, timestamp)))
goto out;
}
}
if (type != '1') {
timestamp_update(self, timestamp);
}
}
if (type == '4') {
/* radarcape-style status message, emit the status event if wanted */
if (self->want_events) {
if (! (messages[message_count++] = make_radarcape_status_event(self, timestamp, data)))
goto out;
}
/* don't try to process this as a Mode S message */
p = m;
continue;
}
if (type == '5') {
/* radarcape-style position message, emit the position event if wanted */
if (self->want_events) {
if (! (messages[message_count++] = make_radarcape_position_event(self, data)))
goto out;
}
/* don't try to process this as a Mode S message */
p = m;
continue;
}
/* it's a Mode A/C or Mode S message, parse it */
if (! (message = modesmessage_from_buffer(timestamp, signal, data, message_len)))
goto out;
/* apply filters, update seen-set */
++self->received_messages;
wanted = filter_message(self, message);
if (wanted < 0)
goto out;
else if (wanted)
messages[message_count++] = message;
else {
++self->suppressed_messages;
Py_DECREF(message);
}
p = m;
}
nomoredata:
if (! (message_tuple = PyTuple_New(message_count)))
goto out;
while (--message_count >= 0) {
PyTuple_SET_ITEM(message_tuple, message_count, messages[message_count]); /* steals ref */
}
rv = Py_BuildValue("(l,N,N)", (long) (p - buffer_start), message_tuple, PyBool_FromLong(error_pending));
out:
while (--message_count >= 0) {
Py_XDECREF(messages[message_count]);
}
free(messages);
return rv;
}
/********** SBS INPUT **************/
/*
* Some notes on this format, as it is poorly documented by Kinetic:
*
* The stream can start at an arbitrary point, the first byte might be mid-packet.
* You need to look for a DLE STX to synchronize with the stream.
* This implementation does that in the Python code to keep this bit simpler; the
* C code assumes it is always given bytes starting at the start of a packet.
*
* You might get arbitrary packet types e.g. AIS interleaved with Mode S messages.
* This implementation doesn't try to interpret them at all, it just reads all
* data until DLE ETX regardless of type and skips those types it doesn't
* understand.
*
* The Mode S CRC values are not the raw bytes from the message; they are the
* residual CRC value after XORing the raw bytes with the calculated CRC over
* the body of the message. That is, a DF17 message with a correct CRC will have
* zeros in the CRC bytes; a DF11 with correct CRC will have the IID in the CRC
* bytes; messages that use Address/Parity will have the address in the CRC bytes.
* To recover the original message, calculate the CRC and XOR it back into the CRC
* bytes. Andrew Whewell says this is probably controlled by a Basestation setting.
*
* The timestamps are measured at the _end_ of the frame, not at the start.
* As frames are variable length, if you want a timestamp anchored to the
* start of the frame (as dump1090 / Beast do), you have to compensate for
* the frame length.
*/
static PyObject *feed_sbs(modesreader *self, Py_buffer *buffer, int max_messages)
{
PyObject *rv = NULL;
uint8_t *buffer_start, *p, *eod;
int message_count = 0;
PyObject *message_tuple = NULL;
PyObject **messages = NULL;
int error_pending = 0;
buffer_start = buffer->buf;
if (max_messages <= 0) {
/* allocate the maximum size we might need, given a minimal encoding of:
* <DLE> <STX> <0x09> <n/a> <3 bytes timestamp> <2 bytes message> <DLE> <ETX> <2 bytes CRC> = 13 bytes total
*/
max_messages = buffer->len / 13 + 1;
}
messages = calloc(max_messages, sizeof(PyObject*));
if (!messages) {
PyErr_NoMemory();
goto out;
}
/* parse messages */
p = buffer_start;
eod = buffer_start + buffer->len;
while (p+13 <= eod && message_count < max_messages) {
int message_len = -1;
uint64_t timestamp;
/* largest message we care about is:
* type 1 byte 0x05 = ADS-B
* spare 1 byte
* timestamp 3 bytes
* data 14 bytes
* total 19 bytes
*/
uint8_t data[19];
uint8_t *m;
int i;
uint8_t type;
uint32_t crc;
PyObject *message;
if (p[0] != 0x10 || p[1] != 0x02) {
error_pending = 1;
if (message_count > 0)
goto nomoredata;
PyErr_Format(PyExc_ValueError, "Lost sync with input stream: expected DLE STX at offset %d but found 0x%02x 0x%02x instead", (int) (p - buffer_start), (int)p[0], (int)p[1]);
goto out;
}
/* scan for DLE ETX, copy data */
m = p + 2;
i = 0;
while (m < eod) {
if (*m == 0x10) {
/* DLE <something> */
if ((m+1) >= eod)
goto nomoredata;
if (m[1] == 0x03) {
/* DLE ETX */
break;
}
if (m[1] != 0x10) {
/* DLE <something we don't understand> */
error_pending = 1;
if (message_count > 0)
goto nomoredata;
PyErr_Format(PyExc_ValueError, "Lost sync with input stream: unexpected DLE 0x%02x at offset %d", (int) (m - buffer_start), (int)m[1]);
goto out;
}
/* DLE DLE */
++m;