I am trying to convert a C module that parses the output from the Linux library rtl_fm. It is used for catching energy usage from an Efergy meter throuh a DVB-T dongle
The C module works fine but I want it written in python to interact with other python modules i have
I have put the constants in constant.py
I am totally stuck in converting the row: cursamp = (int16_t) (fgetc(stdin) | fgetc(stdin)<<8); that I have tried to convert in a lot of different ways. Every try ends with an error!
It seems to be two types of problems: 1. Type conversion of the input result 2. How to convert fgetc() into python.
I also have troubles converting while(!feof(stdin)) into python
Anyone that could help?
C code below:
#include <stdio.h>
#include <stdint.h>
#include <time.h>
#include <math.h>
#include <stdlib.h> // For exit function
#define VOLTAGE 240 /* Refernce Voltage */
#define CENTERSAMP 100 /* Number of samples needed to compute for the wave center */
#define PREAMBLE_COUNT 40 /* Number of high(1) samples for a valid preamble */
#define MINLOWBIT 3 /* Number of high(1) samples for a logic 0 */
#define MINHIGHBIT 8 /* Number of high(1) samples for a logic 1 */
#define E2BYTECOUNT 8 /* Efergy E2 Message Byte Count */
#define FRAMEBITCOUNT 64 /* Number of bits for the entire frame (not including preamble) */
#define LOGTYPE 1 // Allows changing line-endings - 0 is for Unix /n, 1 for Windows /r/n
#define SAMPLES_TO_FLUSH 10 // Number of samples taken before writing to file.
// Setting this too low will cause excessive wear to flash due to updates to
// filesystem! You have been warned! Set to 10 samples for 6 seconds = every min.
int loggingok; // Global var indicating logging on or off
int samplecount; // Global var counter for samples taken since last flush
FILE *fp; // Global var file handle
int calculate_watts(char bytes[])
{
char tbyte;
double current_adc;
double result;
int i;
time_t ltime;
struct tm *curtime;
char buffer[80];
/* add all captured bytes and mask lower 8 bits */
tbyte = 0;
for(i=0;i<7;i++)
tbyte += bytes[i];
tbyte &= 0xff;
/* if checksum matches get watt data */
if (tbyte == bytes[7])
{
time( <ime );
curtime = localtime( <ime );
strftime(buffer,80,"%x,%X", curtime);
current_adc = (bytes[4] * 256) + bytes[5];
result = (VOLTAGE * current_adc) / ((double) 32768 / (double) pow(2,bytes[6]));
printf("%s,%f\n",buffer,result);
if(loggingok) {
if(LOGTYPE) {
fprintf(fp,"%s,%f\r\n",buffer,result);
} else {
fprintf(fp,"%s,%f\n",buffer,result);
}
samplecount++;
if(samplecount==SAMPLES_TO_FLUSH) {
samplecount=0;
fflush(fp);
}
}
fflush(stdout);
return 1;
}
//printf("Checksum Error \n");
return 0;
}
void main (int argc, char**argv)
{
char bytearray[9];
char bytedata;
int prvsamp;
int hctr;
int cursamp;
int bitpos;
int bytecount;
int i;
int preamble;
int frame;
int dcenter;
int dbit;
long center;
if(argc==2) {
fp = fopen(argv[1], "a"); // Log file opened in append mode to avoid destroying data
samplecount=0; // Reset sample counter
loggingok=1;
if (fp == NULL) {
perror("Failed to open log file!"); // Exit if file open fails
exit(EXIT_FAILURE);
}
} else {
loggingok=0;
}
printf("Efergy E2 Classic decode \n\n");
/* initialize variables */
cursamp = 0;
prvsamp = 0;
bytedata = 0;
bytecount = 0;
hctr = 0;
bitpos = 0;
dbit = 0;
preamble = 0;
frame = 0;
dcenter = CENTERSAMP;
center = 0;
while( !feof(stdin) )
{
cursamp = (int16_t) (fgetc(stdin) | fgetc(stdin)<<8);
/* initially capture CENTERSAMP samples for wave center computation */
if (dcenter > 0)
{
dcenter--;
center = center + cursamp; /* Accumulate FSK wave data */
if (dcenter == 0)
{
/* compute for wave center and re-initialize frame variables */
center = (long) (center/CENTERSAMP);
hctr = 0;
bytedata = 0;
bytecount = 0;
bitpos = 0;
dbit = 0;
preamble = 0;
frame = 0;
}
}
else
{
if ((cursamp > center) && (prvsamp < center)) /* Detect for positive edge of frame data */
hctr = 0;
else
if ((cursamp > center) && (prvsamp > center)) /* count samples at high logic */
{
hctr++;
if (hctr > PREAMBLE_COUNT)
preamble = 1;
}
else
if (( cursamp < center) && (prvsamp > center))
{
/* at negative edge */
if ((hctr > MINLOWBIT) && (frame == 1))
{
dbit++;
bitpos++;
bytedata = bytedata << 1;
if (hctr > MINHIGHBIT)
bytedata = bytedata | 0x1;
if (bitpos > 7)
{
bytearray[bytecount] = bytedata;
bytedata = 0;
bitpos = 0;
bytecount++;
if (bytecount == E2BYTECOUNT)
{
/* at this point check for checksum and calculate watt data */
/* if there is a checksum mismatch compute for a new wave center */
if (calculate_watts(bytearray) == 0)
dcenter = CENTERSAMP; /* make dcenter non-zero to trigger center resampling */
}
}
if (dbit > FRAMEBITCOUNT)
{
/* reset frame variables */
bitpos = 0;
bytecount = 0;
dbit = 0;
frame = 0;
preamble = 0;
bytedata = 0;
}
}
hctr = 0;
}
else
hctr = 0;
if ((hctr == 0) && (preamble == 1))
{
/* end of preamble, start of frame data */
preamble = 0;
frame = 1;
}
} /* dcenter */
prvsamp = cursamp;
} /* while */
if(loggingok) {
fclose(fp); // If rtl-fm gives EOF and program terminates, close file gracefully.
}
}
And the Python conversion (a little simplified without file logging):
from datetime import date
from datetime import time
from datetime import datetime
import cmath
import constant
import sys
import logging
logging.basicConfig(level=logging.DEBUG)
logger = logging.getLogger(__name__)
class _Getch:
"""Gets a single character from standard input. Does not echo to the
screen."""
def __init__(self):
try:
self.impl = _GetchWindows()
except ImportError:
self.impl = _GetchUnix()
def __call__(self): return self.impl()
class _GetchUnix:
def __init__(self):
import tty, sys
def __call__(self):
import sys, tty, termios
fd = sys.stdin.fileno()
old_settings = termios.tcgetattr(fd)
try:
tty.setraw(sys.stdin.fileno())
ch = sys.stdin.read(1)
finally:
termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
return ch
class _GetchWindows:
def __init__(self):
import msvcrt
def __call__(self):
import msvcrt
return msvcrt.getch()
getch = _Getch()
def calculate_watts(*args):
logger.info('Start Calculation')
now = datetime.now()
tbyte = 0
for i in range(0,7):
tbyte += bytes[i]
tbyte = tbyte & 0xff
if (tbyte == bytes[7]):
current_adc = (bytes[4] * 256) + bytes[5]
result = (constant.VOLTAGE * current_adc) / (32768 / pow(2,bytes[6]))
print "%s,%f\n" % (now,result)
exit(0)
else:
print "Checksum Error \n"
exit(1)
def main(*argv):
logger.info('Starting Main')
print "Efergy E2 Python decode \n\n"
cursamp = 0
prvsamp = 0
bytedata = 0
bytecount = 0
hctr = 0
bitpos = 0
dbit = 0
preamble = 0
frame = 0
dcenter = constant.CENTERSAMP
center = 0
while (1):
cursamp = (int)((int)(_Getch()) | (int)(_Getch())<<8)
logger.debug('cursamp: %f',cursamp)
if (dcenter > 0):
dcenter -= 1
center = center + cursamp #/* Accumulate FSK wave data */
if (dcenter == 0):
center = (center/constant.CENTERSAMP)
hctr = 0
bytedata = 0
bytecount = 0
bitpos = 0
dbit = 0
preamble = 0
frame = 0
else:
if ((cursamp > center) and (prvsamp < center)): #/* Detect for positive edge of frame data */
hctr = 0
else:
if ((cursamp > center) and (prvsamp > center)): #/* count samples at high logic */
hctr += 1
if (hctr > constant.PREAMBLE_COUNT):
preamble = 1
else:
if (( cursamp < center) and (prvsamp > center)):
#/* at negative edge */
if ((hctr > constant.MINLOWBIT) and (frame == 1)):
dbit += 1
bitpos += 1
bytedata = bytedata << 1
if (hctr > constant.MINHIGHBIT):
bytedata = bytedata | 0x1
if (bitpos > 7):
bytearray[bytecount] = bytedata
bytedata = 0
bitpos = 0
bytecount += 1
if (bytecount == constant.E2BYTECOUNT):
# /* at this point check for checksum and calculate watt data */
# /* if there is a checksum mismatch compute for a new wave center */
if (calculate_watts(bytearray) == 0):
dcenter = constant.CENTERSAMP #/* make dcenter non-zero to trigger center resampling */
if (dbit > constant.FRAMEBITCOUNT):
#/* reset frame variables */
bitpos = 0
bytecount = 0
dbit = 0
frame = 0
preamble = 0
bytedata = 0
hctr = 0
else:
hctr = 0
if ((hctr == 0) and (preamble == 1)):
#/* end of preamble, start of frame data */
preamble = 0
frame = 1
#/* dcenter */
prvsamp = cursamp
if __name__ == "__main__":
main()
