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can-utils
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Fixed calculation of needed bits on the physical wire according Ken Tindells 

*worst* case calculation for stuff-bits.
(see "Guaranteeing Message Latencies on Controller Area Network" 1st ICC'94)
Due to the bitstuffing estimation the calculated busload may exceed 100%.
pull/7/head
Oliver Hartkopp 2010-09-24 17:56:53 +00:00
parent f5576a9833
commit d7fe33eb4b
1 changed files with 37 additions and 6 deletions
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43
canbusload.c
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@ -88,6 +88,7 @@ static unsigned char redraw;
static unsigned char timestamp;
static unsigned char color;
static unsigned char bargraph;
static unsigned char ignore_bitstuffing;
static char *prg;
void print_usage(char *prg)
@ -98,11 +99,13 @@ void print_usage(char *prg)
fprintf(stderr, " -c (colorize lines)\n");
fprintf(stderr, " -b (show bargraph in %d%% resolution)\n", PERCENTRES);
fprintf(stderr, " -r (redraw the terminal - similar to top)\n");
fprintf(stderr, " -i (ignore bitstuffing estimation in bandwith calculation)\n");
fprintf(stderr, "\n");
fprintf(stderr, "Up to %d CAN interfaces with mandatory bitrate can be specified on the \n", MAXSOCK);
fprintf(stderr, "commandline in the form: <ifname>@<bitrate>\n\n");
fprintf(stderr, "The bitrate is mandatory as it is needed to know the CAN bus bitrate to\n");
fprintf(stderr, "calcultate the bus load percentage based on the received CAN frames.\n");
fprintf(stderr, "Due to the bitstuffing estimation the calculated busload may exceed 100%%.\n");
fprintf(stderr, "For each given interface the data is presented in one line which contains:\n\n");
fprintf(stderr, "(interface) (received CAN frames) (used bits total) (used bits for payload)\n");
fprintf(stderr, "\nExample:\n");
@ -174,6 +177,9 @@ void printstats(int signo)
printf(" |");
if (percent > 100)
percent = 100;
for (j=0; j < NUMBAR; j++){
if (j < percent/PERCENTRES)
printf("X");
@ -220,7 +226,7 @@ int main(int argc, char **argv)
prg = basename(argv[0]);
while ((opt = getopt(argc, argv, "rtbch?")) != -1) {
while ((opt = getopt(argc, argv, "rtbcih?")) != -1) {
switch (opt) {
case 'r':
redraw = 1;
@ -238,6 +244,10 @@ int main(int argc, char **argv)
color = 1;
break;
case 'i':
ignore_bitstuffing = 1;
break;
default:
print_usage(prg);
exit(1);
@ -365,11 +375,32 @@ int main(int argc, char **argv)
stat[i].recv_frames++;
stat[i].recv_bits_payload += frame.can_dlc*8;
stat[i].recv_bits_total += frame.can_dlc*8;
if (frame.can_id & CAN_EFF_FLAG)
stat[i].recv_bits_total += 67;
else
stat[i].recv_bits_total += 47;
/*
* Following Ken Tindells *worst* case calculation for stuff-bits
* (see "Guaranteeing Message Latencies on Controller Area Network" 1st ICC'94)
* the needed bits on the wire can be calculated as:
*
* (34 + 8n)/5 + 47 + 8n for SFF frames (11 bit CAN-ID) => (269 + 48n)/5
* (54 + 8n)/5 + 67 + 8n for EFF frames (29 bit CAN-ID) => (389 + 48n)/5
*
* while 'n' is the data length code (number of payload bytes)
*
*/
if (ignore_bitstuffing) {
/* calculation without bitstuffing */
if (frame.can_id & CAN_EFF_FLAG)
stat[i].recv_bits_total += 67 + frame.can_dlc*8;
else
stat[i].recv_bits_total += 47 + frame.can_dlc*8;
} else {
/* needed bits including estimated worst case stuff bits */
if (frame.can_id & CAN_EFF_FLAG)
stat[i].recv_bits_total += (389 + frame.can_dlc*48)/5;
else
stat[i].recv_bits_total += (269 + frame.can_dlc*48)/5;
}
}
}
}