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canbusload: Add exact CAN frame length calculation (including bitstuffing)

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This adds an algorithm for calculating the exact number of bits a CAN
frame occupies on the bus and uses this algorithm in canbusload. It
also moves the other methods for CAN frame length calculation, already
present in canbusload, to the new file.

The added algorithm calculates the exact number of stuffed bit in a
CAN frame. Note that in order to calculate that correctly, we must
also know the frame's CRC. Hence, the algorithm also includes CRC
calculation routine.

The correctness of the algorithm was verified on an oscilloscope for
several different SFF and EFF frames.

Currently only CAN frames are supported. For CANFD frames, a different
algorithm is needed. CANFD uses different CRC polynomials and
calculates the CRC from the staffed bit-stream (CAN calculates CRC
from de-stuffed bit-stream).

Signed-off-by: Michal Sojka <sojkam1@fel.cvut.cz>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This commit is contained in:
Michal Sojka
2014-01-30 16:23:25 +01:00
committed by Marc Kleine-Budde
parent 4ddde7b966
commit 2206f92de7
5 changed files with 305 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files
canbusload.c
+12 -30
View File
@@ -61,6 +61,7 @@
#include <linux/can/raw.h>
#include "terminal.h"
#include "canframelen.h"
#define MAXSOCK 16 /* max. number of CAN interfaces given on the cmdline */
@@ -84,7 +85,7 @@ static unsigned char redraw;
static unsigned char timestamp;
static unsigned char color;
static unsigned char bargraph;
static unsigned char ignore_bitstuffing;
static enum cfl_mode mode = CFL_WORSTCASE;
static char *prg;
void print_usage(char *prg)
@@ -95,7 +96,8 @@ 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 bandwidth calculation)\n");
fprintf(stderr, " -i (ignore bitstuffing in bandwidth calculation)\n");
fprintf(stderr, " -e (exact calculation of stuffed bits)\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");
@@ -223,7 +225,7 @@ int main(int argc, char **argv)
prg = basename(argv[0]);
while ((opt = getopt(argc, argv, "rtbcih?")) != -1) {
while ((opt = getopt(argc, argv, "rtbcieh?")) != -1) {
switch (opt) {
case 'r':
redraw = 1;
@@ -242,7 +244,11 @@ int main(int argc, char **argv)
break;
case 'i':
ignore_bitstuffing = 1;
mode = CFL_NO_BITSTUFFING;
break;
case 'e':
mode = CFL_EXACT;
break;
default:
@@ -372,32 +378,8 @@ int main(int argc, char **argv)
stat[i].recv_frames++;
stat[i].recv_bits_payload += frame.can_dlc*8;
/*
* 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;
}
stat[i].recv_bits_total += can_frame_length((struct canfd_frame*)&frame,
mode, sizeof(frame));
}
}
}