#ifdef CONFIG_CAN_CALC_BITTIMING
#define CAN_CALC_MAX_ERROR 50 /* in one-tenth of a percent */
+#define CAN_CALC_SYNC_SEG 1
/*
* Bit-timing calculation derived from:
* registers of the CAN controller. You can find more information
* 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)
+static int can_update_sample_point(const struct can_bittiming_const *btc,
+ unsigned int sample_point_nominal, unsigned int tseg,
+ unsigned int *tseg1_ptr, unsigned int *tseg2_ptr,
+ unsigned int *sample_point_error_ptr)
{
- *tseg2 = tseg + 1 - (sampl_pt * (tseg + 1)) / 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 sample_point_error, best_sample_point_error = UINT_MAX;
+ unsigned int sample_point, best_sample_point = 0;
+ unsigned int tseg1, tseg2;
+ int i;
+
+ for (i = 0; i <= 1; i++) {
+ tseg2 = tseg + CAN_CALC_SYNC_SEG - (sample_point_nominal * (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;
+ }
+
+ sample_point = 1000 * (tseg + CAN_CALC_SYNC_SEG - tseg2) / (tseg + CAN_CALC_SYNC_SEG);
+ sample_point_error = abs(sample_point_nominal - sample_point);
+
+ if ((sample_point <= sample_point_nominal) && (sample_point_error < best_sample_point_error)) {
+ best_sample_point = sample_point;
+ best_sample_point_error = sample_point_error;
+ *tseg1_ptr = tseg1;
+ *tseg2_ptr = tseg2;
+ }
}
- return 1000 * (tseg + 1 - *tseg2) / (tseg + 1);
+
+ if (sample_point_error_ptr)
+ *sample_point_error_ptr = best_sample_point_error;
+
+ return best_sample_point;
}
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 bitrate; /* current bitrate */
+ unsigned int bitrate_error; /* difference between current and nominal value */
+ unsigned int best_bitrate_error = UINT_MAX;
+ unsigned int sample_point_error; /* difference between current and nominal value */
+ unsigned int best_sample_point_error = UINT_MAX;
+ unsigned int sample_point_nominal; /* nominal 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 = 0, tseg2 = 0;
u64 v64;
/* Use CiA recommended sample points */
if (bt->sample_point) {
- sampl_pt = bt->sample_point;
+ sample_point_nominal = bt->sample_point;
} else {
if (bt->bitrate > 800000)
- sampl_pt = 750;
+ sample_point_nominal = 750;
else if (bt->bitrate > 500000)
- sampl_pt = 800;
+ sample_point_nominal = 800;
else
- sampl_pt = 875;
+ sample_point_nominal = 875;
}
/* tseg even = round down, odd = round up */
for (tseg = (btc->tseg1_max + btc->tseg2_max) * 2 + 1;
tseg >= (btc->tseg1_min + btc->tseg2_min) * 2; tseg--) {
- tsegall = 1 + tseg / 2;
+ tsegall = CAN_CALC_SYNC_SEG + tseg / 2;
+
/* 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;
+
+ bitrate = priv->clock.freq / (brp * tsegall);
+ bitrate_error = abs(bt->bitrate - bitrate);
+
/* tseg brp biterror */
- if (error < 0)
- error = -error;
- if (error > best_error)
+ if (bitrate_error > best_bitrate_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 (bitrate_error < best_bitrate_error)
+ best_sample_point_error = UINT_MAX;
+
+ can_update_sample_point(btc, sample_point_nominal, tseg / 2, &tseg1, &tseg2, &sample_point_error);
+ if (sample_point_error > best_sample_point_error)
+ continue;
+
+ best_sample_point_error = sample_point_error;
+ best_bitrate_error = bitrate_error;
best_tseg = tseg / 2;
best_brp = brp;
- if (error == 0)
+
+ if (bitrate_error == 0 && sample_point_error == 0)
break;
}
- if (best_error) {
+ if (best_bitrate_error) {
/* Error in one-tenth of a percent */
- error = (best_error * 1000) / bt->bitrate;
- if (error > CAN_CALC_MAX_ERROR) {
+ v64 = (u64)best_bitrate_error * 1000;
+ do_div(v64, bt->bitrate);
+ bitrate_error = (u32)v64;
+ if (bitrate_error > CAN_CALC_MAX_ERROR) {
netdev_err(dev,
- "bitrate error %ld.%ld%% too high\n",
- error / 10, error % 10);
+ "bitrate error %d.%d%% too high\n",
+ bitrate_error / 10, bitrate_error % 10);
return -EDOM;
- } else {
- netdev_warn(dev, "bitrate error %ld.%ld%%\n",
- error / 10, error % 10);
}
+ netdev_warn(dev, "bitrate error %d.%d%%\n",
+ bitrate_error / 10, bitrate_error % 10);
}
/* real sample point */
- bt->sample_point = can_update_spt(btc, sampl_pt, best_tseg,
- &tseg1, &tseg2);
+ bt->sample_point = can_update_sample_point(btc, sample_point_nominal, 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 * (tseg1 + tseg2 + 1));
+
+ /* real bitrate */
+ bt->bitrate = priv->clock.freq / (bt->brp * (CAN_CALC_SYNC_SEG + tseg1 + tseg2));
return 0;
}
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