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%.

git-svn-id: svn://svn.berlios.de//socketcan/trunk@1195 030b6a49-0b11-0410-94ab-b0dab22257f2

diff --git a/can-utils/canbusload.c b/can-utils/canbusload.c
index 36f3423e0aca9f24d6e7883c9e6fced729532d3d..26323d269ed1a45282418cfe53029ed141b78812 100644 (file)
--- a/can-utils/canbusload.c
+++ b/can-utils/canbusload.c
@@ -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;
+                               }
                        }
                }
        }