/* can-calc-bit-timing.c: Calculate CAN bit timing parameters
*
* Copyright (C) 2008 Wolfgang Grandegger <wg@grandegger.com>
+ * Copyright (C) 2016 Marc Kleine-Budde <mkl@pengutronix.de>
*
* Derived from:
* can_baud.c - CAN baudrate calculation
#include <errno.h>
#include <getopt.h>
+#include <limits.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
* in the header file linux/can/netlink.h.
*/
static int can_update_spt(const struct can_bittiming_const *btc,
- int sampl_pt, int tseg, int *tseg1, int *tseg2)
+ unsigned int spt_target, unsigned int tseg,
+ unsigned int *tseg1_ptr, unsigned int *tseg2_ptr,
+ unsigned int *spt_error_ptr)
{
- *tseg2 = tseg + CAN_CALC_SYNC_SEG -
- (sampl_pt * (tseg + CAN_CALC_SYNC_SEG)) / 1000;
- if (*tseg2 < btc->tseg2_min)
- *tseg2 = btc->tseg2_min;
- if (*tseg2 > btc->tseg2_max)
- *tseg2 = btc->tseg2_max;
- *tseg1 = tseg - *tseg2;
- if (*tseg1 > btc->tseg1_max) {
- *tseg1 = btc->tseg1_max;
- *tseg2 = tseg - *tseg1;
+ unsigned int spt_error, best_spt_error = UINT_MAX;
+ unsigned int spt, best_spt = 0;
+ unsigned int tseg1, tseg2;
+ int i;
+
+ for (i = 0; i <= 1; i++) {
+ tseg2 = tseg + CAN_CALC_SYNC_SEG - (spt_target * (tseg + CAN_CALC_SYNC_SEG)) / 1000 - i;
+ tseg2 = clamp(tseg2, btc->tseg2_min, btc->tseg2_max);
+ tseg1 = tseg - tseg2;
+ if (tseg1 > btc->tseg1_max) {
+ tseg1 = btc->tseg1_max;
+ tseg2 = tseg - tseg1;
+ }
+
+ spt = 1000 * (tseg + CAN_CALC_SYNC_SEG - tseg2) / (tseg + CAN_CALC_SYNC_SEG);
+ spt_error = abs(spt_target - spt);
+
+ if ((spt <= spt_target) && (spt_error < best_spt_error)) {
+ best_spt = spt;
+ best_spt_error = spt_error;
+ *tseg1_ptr = tseg1;
+ *tseg2_ptr = tseg2;
+ }
}
- return 1000 * (tseg + CAN_CALC_SYNC_SEG - *tseg2) / (tseg + CAN_CALC_SYNC_SEG);
+
+ if (spt_error_ptr)
+ *spt_error_ptr = best_spt_error;
+
+ return best_spt;
}
static int can_calc_bittiming(struct net_device *dev, struct can_bittiming *bt,
const struct can_bittiming_const *btc)
{
struct can_priv *priv = netdev_priv(dev);
- long best_error = 1000000000, error = 0;
- int best_tseg = 0, best_brp = 0, brp = 0;
- int tsegall, tseg = 0, tseg1 = 0, tseg2 = 0;
- int spt_error = 1000, spt = 0, sampl_pt;
- long rate;
+ unsigned int rate; /* current bitrate */
+ unsigned int rate_error; /* difference between current and target value */
+ unsigned int best_rate_error = UINT_MAX;
+ unsigned int spt_error; /* difference between current and target value */
+ unsigned int best_spt_error = UINT_MAX;
+ unsigned int spt_target; /* target sample point */
+ unsigned int best_tseg = 0; /* current best value for tseg */
+ unsigned int best_brp = 0; /* current best value for brp */
+ unsigned int brp, tsegall, tseg, tseg1, tseg2;
u64 v64;
/* Use CiA recommended sample points */
if (bt->sample_point) {
- sampl_pt = bt->sample_point;
+ spt_target = bt->sample_point;
} else {
if (bt->bitrate > 800000)
- sampl_pt = 750;
+ spt_target = 750;
else if (bt->bitrate > 500000)
- sampl_pt = 800;
+ spt_target = 800;
else
- sampl_pt = 875;
+ spt_target = 875;
}
/* tseg even = round down, odd = round up */
/* Compute all possible tseg choices (tseg=tseg1+tseg2) */
brp = priv->clock.freq / (tsegall * bt->bitrate) + tseg % 2;
- /* chose brp step which is possible in system */
+
+ /* choose brp step which is possible in system */
brp = (brp / btc->brp_inc) * btc->brp_inc;
if ((brp < btc->brp_min) || (brp > btc->brp_max))
continue;
+
rate = priv->clock.freq / (brp * tsegall);
- error = bt->bitrate - rate;
+ rate_error = abs(bt->bitrate - rate);
+
/* tseg brp biterror */
- if (error < 0)
- error = -error;
- if (error > best_error)
+ if (rate_error > best_rate_error)
continue;
- best_error = error;
- if (error == 0) {
- spt = can_update_spt(btc, sampl_pt, tseg / 2,
- &tseg1, &tseg2);
- error = sampl_pt - spt;
- if (error < 0)
- error = -error;
- if (error > spt_error)
- continue;
- spt_error = error;
- }
+
+ /* reset sample point error if we have a better bitrate */
+ if (rate_error < best_rate_error)
+ best_spt_error = UINT_MAX;
+
+ can_update_spt(btc, spt_target, tseg / 2, &tseg1, &tseg2, &spt_error);
+ if (spt_error > best_spt_error)
+ continue;
+
+ best_spt_error = spt_error;
+ best_rate_error = rate_error;
best_tseg = tseg / 2;
best_brp = brp;
- if (error == 0)
+
+ if (rate_error == 0 && spt_error == 0)
break;
}
- if (best_error) {
+ if (best_rate_error) {
/* Error in one-tenth of a percent */
- error = (best_error * 1000) / bt->bitrate;
- if (error > CAN_CALC_MAX_ERROR) {
+ rate_error = (best_rate_error * 1000) / bt->bitrate;
+ if (rate_error > CAN_CALC_MAX_ERROR) {
netdev_err(dev,
"bitrate error %ld.%ld%% too high\n",
- error / 10, error % 10);
+ rate_error / 10, rate_error % 10);
return -EDOM;
}
netdev_warn(dev, "bitrate error %ld.%ld%%\n",
- error / 10, error % 10);
+ rate_error / 10, rate_error % 10);
}
/* real sample point */
- bt->sample_point = can_update_spt(btc, sampl_pt, best_tseg,
- &tseg1, &tseg2);
+ bt->sample_point = can_update_spt(btc, spt_target, best_tseg,
+ &tseg1, &tseg2, NULL);
- v64 = (u64)best_brp * 1000000000UL;
+ v64 = (u64)best_brp * 1000 * 1000 * 1000;
do_div(v64, priv->clock.freq);
bt->tq = (u32)v64;
bt->prop_seg = tseg1 / 2;
bt->phase_seg2 = tseg2;
/* check for sjw user settings */
- if (!bt->sjw || !btc->sjw_max)
+ if (!bt->sjw || !btc->sjw_max) {
bt->sjw = 1;
- else {
+ } else {
/* bt->sjw is at least 1 -> sanitize upper bound to sjw_max */
if (bt->sjw > btc->sjw_max)
bt->sjw = btc->sjw_max;
}
bt->brp = best_brp;
+
/* real bit-rate */
bt->bitrate = priv->clock.freq / (bt->brp * (CAN_CALC_SYNC_SEG + tseg1 + tseg2));
if (!sample_point)
sample_point = get_cia_sample_point(bitrate);
- rate_error = abs((__s32)(bitrate - bt.bitrate));
- spt_error = abs((__s32)(sample_point - bt.sample_point));
+ rate_error = abs(bitrate - bt.bitrate);
+ spt_error = abs(sample_point - bt.sample_point);
printf("%7d "
"%6d %3d %4d %4d "
{
__u32 bitrate = 0;
__u32 opt_ref_clk = 0, ref_clk;
- int sampl_pt = 0;
+ unsigned int spt_target = 0;
bool quiet = false, list = false, found = false;
char *name = NULL;
unsigned int i, j;
break;
case 'c':
- opt_ref_clk = atoi(optarg);
+ opt_ref_clk = strtoul(optarg, NULL, 10);
break;
case 'l':
break;
case 's':
- sampl_pt = atoi(optarg);
+ spt_target = strtoul(optarg, NULL, 10);
break;
default:
exit(EXIT_SUCCESS);
}
- if (sampl_pt && (sampl_pt >= 1000 || sampl_pt < 100))
+ if (spt_target && (spt_target >= 1000 || spt_target < 100))
print_usage(argv[0]);
for (i = 0; i < ARRAY_SIZE(can_calc_consts); i++) {
ref_clk = btc->ref_clk;
if (bitrate) {
- print_bit_timing(btc, bitrate, sampl_pt, ref_clk, quiet);
+ print_bit_timing(btc, bitrate, spt_target, ref_clk, quiet);
} else {
for (j = 0; j < ARRAY_SIZE(common_bitrates); j++)
print_bit_timing(btc, common_bitrates[j],
- sampl_pt, ref_clk, j);
+ spt_target, ref_clk, j);
}
printf("\n");
}