Hello, while writing the commit message I noticed the "the sample point error must be equal or smaller" in condition 2 (see below).
This means if there are more than one timing parameters which provide the same bit rate and sample point error the algorithm chooses the one with the highest brp, resulting in a shorter time quanta. >From my non CAN expert point of view this affects the parameters which have a fixed value of "1" timequanta. e.g. the SJW. Can the real CAN expert comment on this? Is it better to have a small or a large timequanta? cheers, Marc >From b91926f0c706fa05425a58b92cedb690577d10cb Mon Sep 17 00:00:00 2001 From: Marc Kleine-Budde <[email protected]> Date: Sat, 15 May 2010 18:26:03 +0200 Subject: [PATCH 5/5] can-calc-bit-timing: better sample point calculation This patch tries to optimize the calculation of the sample point. To understand what it does have a look at the original implementation. If there is a combination of timing parameters where both the bitrate and sample point error are 0 the current implementation has a pretty good change of finding it (maybe it will always do, but I'm to lazy to proof this). However if the reference clock doesn't allow an optimal bitrate (this means the bitrate error is always != 0) there might be several timing parameter combinations having the same bitrate error. The original implementation will allways choose the one with the highest brp. The actual sample point error isn't taken into account. This patch changes the algorithm to minimize the sample point error, too. Now a brp/tseg combination is accepted as better if one of these condition are fulfilled: 1) the bit rate error must be smaller, or 2) the bit rate error must be equal and the sample point error must be equal or smaller If a smaller bit rate error is found the sample point error is reset. This ensures that we first optimize for small bit rate error and then for small sample point errors. The following diff shows the sample point error improvements. --- orig.txt 2010-05-17 00:10:21.000000000 +0200 +++ new.txt 2010-05-17 00:10:05.000000000 +0200 @@ -27,9 +27,9 @@ Bit timing parameters for mscan with 33.000000 MHz ref clock nominal real Bitrt nom real SampP Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error BTR0 BTR1 1000000 90 3 4 3 1 3 1000000 0.0% 75.0% 72.7% 3.1% 0x02 0x26 - 800000 181 2 2 2 1 6 785714 1.8% 80.0% 71.4% 10.8% 0x05 0x13 + 800000 90 5 5 3 1 3 785714 1.8% 80.0% 78.5% 1.9% 0x02 0x29 500000 181 4 4 2 1 6 500000 0.0% 87.5% 81.8% 6.5% 0x05 0x17 250000 333 4 5 2 1 11 250000 0.0% 87.5% 83.3% 4.8% 0x0a 0x18 125000 666 4 5 2 1 22 125000 0.0% 87.5% 83.3% 4.8% 0x15 0x18 100000 666 6 6 2 1 22 100000 0.0% 87.5% 86.6% 1.0% 0x15 0x1b @@ -40,12 +40,12 @@ Bit timing parameters for mscan with 33.300000 MHz ref clock nominal real Bitrt nom real SampP Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error BTR0 BTR1 1000000 90 3 4 3 1 3 1009090 0.9% 75.0% 72.7% 3.1% 0x02 0x26 - 800000 180 2 2 2 1 6 792857 0.9% 80.0% 71.4% 10.8% 0x05 0x13 + 800000 90 5 5 3 1 3 792857 0.9% 80.0% 78.5% 1.9% 0x02 0x29 500000 180 4 4 2 1 6 504545 0.9% 87.5% 81.8% 6.5% 0x05 0x17 - 250000 570 2 2 2 1 19 250375 0.1% 87.5% 71.4% 18.4% 0x12 0x13 - 125000 1141 2 2 2 1 38 125187 0.1% 87.5% 71.4% 18.4% 0x25 0x13 + 250000 210 7 8 3 1 7 250375 0.1% 87.5% 84.2% 3.8% 0x06 0x2e + 125000 570 5 6 2 1 19 125187 0.1% 87.5% 85.7% 2.1% 0x12 0x1a 100000 1111 3 3 2 1 37 100000 0.0% 87.5% 77.7% 11.2% 0x24 0x15 50000 1111 7 7 3 1 37 50000 0.0% 87.5% 83.3% 4.8% 0x24 0x2d 20000 ***bitrate not possible*** 10000 ***bitrate not possible*** @@ -53,12 +53,12 @@ Bit timing parameters for mscan with 33.333333 MHz ref clock nominal real Bitrt nom real SampP Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error BTR0 BTR1 1000000 90 3 4 3 1 3 1010101 1.0% 75.0% 72.7% 3.1% 0x02 0x26 - 800000 180 2 2 2 1 6 793650 0.8% 80.0% 71.4% 10.8% 0x05 0x13 + 800000 90 5 5 3 1 3 793650 0.8% 80.0% 78.5% 1.9% 0x02 0x29 500000 180 4 4 2 1 6 505050 1.0% 87.5% 81.8% 6.5% 0x05 0x17 - 250000 570 2 2 2 1 19 250626 0.3% 87.5% 71.4% 18.4% 0x12 0x13 - 125000 1140 2 2 2 1 38 125313 0.3% 87.5% 71.4% 18.4% 0x25 0x13 + 250000 210 7 8 3 1 7 250626 0.3% 87.5% 84.2% 3.8% 0x06 0x2e + 125000 570 5 6 2 1 19 125313 0.3% 87.5% 85.7% 2.1% 0x12 0x1a 100000 1110 3 3 2 1 37 100100 0.1% 87.5% 77.7% 11.2% 0x24 0x15 50000 870 8 8 6 1 29 49975 0.1% 87.5% 73.9% 15.5% 0x1c 0x5f 20000 ***bitrate not possible*** 10000 ***bitrate not possible*** @@ -78,12 +78,12 @@ Bit timing parameters for at91 with 99.532800 MHz ref clock nominal real Bitrt nom real SampP Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error CAN_BR -1000000 100 3 3 3 1 10 995328 0.5% 75.0% 70.0% 6.7% 0x00090222 +1000000 50 7 7 5 1 5 995328 0.5% 75.0% 75.0% 0.0% 0x00040664 800000 50 8 8 8 1 5 796262 0.5% 80.0% 68.0% 15.0% 0x00040777 - 500000 251 2 3 2 1 25 497664 0.5% 87.5% 75.0% 14.3% 0x00180121 - 250000 572 2 2 2 1 57 249455 0.2% 87.5% 71.4% 18.4% 0x00380111 + 500000 100 8 8 3 1 10 497664 0.5% 87.5% 85.0% 2.9% 0x00090772 + 250000 210 7 8 3 1 21 249455 0.2% 87.5% 84.2% 3.8% 0x00140672 125000 532 6 6 2 1 53 125198 0.2% 87.5% 86.6% 1.0% 0x00340551 100000 833 4 5 2 1 83 99932 0.1% 87.5% 83.3% 4.8% 0x00520341 50000 833 8 8 7 1 83 49966 0.1% 87.5% 70.8% 19.1% 0x00520776 20000 ***bitrate not possible*** @@ -92,22 +92,22 @@ Bit timing parameters for flexcan with 49.875000 MHz ref clock nominal real Bitrt nom real SampP Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error CAN_CTRL 1000000 100 3 3 3 1 5 997500 0.2% 75.0% 70.0% 6.7% 0x04120002 - 800000 180 2 2 2 1 9 791666 1.0% 80.0% 71.4% 10.8% 0x08090001 - 500000 200 3 4 2 1 10 498750 0.2% 87.5% 80.0% 8.6% 0x09190002 - 250000 501 2 3 2 1 25 249375 0.2% 87.5% 75.0% 14.3% 0x18110001 + 800000 140 3 3 2 1 7 791666 1.0% 80.0% 77.7% 2.9% 0x06110002 + 500000 100 8 8 3 1 5 498750 0.2% 87.5% 85.0% 2.9% 0x043a0007 + 250000 200 8 8 3 1 10 249375 0.2% 87.5% 85.0% 2.9% 0x093a0007 125000 421 7 8 3 1 21 125000 0.0% 87.5% 84.2% 3.8% 0x143a0006 - 100000 1002 3 4 2 1 50 99750 0.2% 87.5% 80.0% 8.6% 0x31190002 + 100000 501 8 8 3 1 25 99750 0.2% 87.5% 85.0% 2.9% 0x183a0007 50000 1664 4 5 2 1 83 50075 0.1% 87.5% 83.3% 4.8% 0x52210003 20000 3568 5 6 2 1 178 20014 0.1% 87.5% 85.7% 2.1% 0xb1290004 10000 4350 8 8 6 1 217 9992 0.1% 87.5% 73.9% 15.5% 0xd83d0007 Bit timing parameters for flexcan with 66.500000 MHz ref clock nominal real Bitrt nom real SampP Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error CAN_CTRL 1000000 90 3 4 3 1 6 1007575 0.8% 75.0% 72.7% 3.1% 0x051a0002 - 800000 180 2 2 2 1 12 791666 1.0% 80.0% 71.4% 10.8% 0x0b090001 + 800000 90 5 5 3 1 6 791666 1.0% 80.0% 78.5% 1.9% 0x05220004 500000 105 7 8 3 1 7 500000 0.0% 87.5% 84.2% 3.8% 0x063a0006 250000 285 5 6 2 1 19 250000 0.0% 87.5% 85.7% 2.1% 0x12290004 125000 571 5 6 2 1 38 125000 0.0% 87.5% 85.7% 2.1% 0x25290004 100000 526 7 8 3 1 35 100000 0.0% 87.5% 84.2% 3.8% 0x223a0006 Signed-off-by: Marc Kleine-Budde <[email protected]> --- can-calc-bit-timing.c | 71 +++++++++++++++++++++++++++---------------------- 1 files changed, 39 insertions(+), 32 deletions(-) diff --git a/can-calc-bit-timing.c b/can-calc-bit-timing.c index 95bc796..6364cb1 100644 --- a/can-calc-bit-timing.c +++ b/can-calc-bit-timing.c @@ -1,6 +1,7 @@ /* can-calc-bit-timing.c: Calculate CAN bit timing parameters * * Copyright (C) 2008 Wolfgang Grandegger <[email protected]> + * Copyright (C) 2010 Marc Kleine-Budde <[email protected]> * * Derived from: * can_baud.c - CAN baudrate calculation @@ -401,18 +402,17 @@ static long common_bitrates[] = { #define CAN_CALC_MAX_ERROR 50 /* in one-tenth of a percent */ static int can_update_spt(const struct can_bittiming_const *btc, - int sampl_pt, int tseg, int *tseg1, int *tseg2) + unsigned int sampl_pt, unsigned int tseg, + unsigned int *tseg1, unsigned int *tseg2) { *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; + *tseg2 = clamp(*tseg2, btc->tseg2_min, btc->tseg2_max); *tseg1 = tseg - *tseg2; if (*tseg1 > btc->tseg1_max) { *tseg1 = btc->tseg1_max; *tseg2 = tseg - *tseg1; } + return 1000 * (tseg + 1 - *tseg2) / (tseg + 1); } @@ -420,11 +420,15 @@ static int can_calc_bittiming(struct net_device *dev, struct can_bittiming *bt) { struct can_priv *priv = netdev_priv(dev); const struct can_bittiming_const *btc = priv->bittiming_const; - long rate, best_rate = 0; - 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; /* current bitrate */ + long rate_error; /* difference between current and target value */ + long best_rate_error = 1000000000; + int spt; /* current sample point in thousandth */ + int spt_error; /* difference between current and target value */ + int best_spt_error = 1000; + int sampl_pt; /* target sample point */ + int best_tseg = 0, best_brp = 0; /* current best values for tseg and brp */ + unsigned int brp, tsegall, tseg, tseg1, tseg2; u64 v64; if (!priv->bittiming_const) @@ -446,48 +450,51 @@ static int can_calc_bittiming(struct net_device *dev, struct can_bittiming *bt) for (tseg = (btc->tseg1_max + btc->tseg2_max) * 2 + 1; tseg >= (btc->tseg1_min + btc->tseg2_min) * 2; tseg--) { tsegall = 1 + 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 */ 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((long)(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 = 1000; + + spt = can_update_spt(btc, sampl_pt, tseg / 2, &tseg1, &tseg2); + spt_error = abs((long)(sampl_pt - spt)); + if (spt_error > best_spt_error) + continue; + + best_spt_error = spt_error; + best_rate_error = rate_error; best_tseg = tseg / 2; best_brp = brp; - best_rate = rate; - 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) { dev_err(dev->dev.parent, "bitrate error %ld.%ld%% too high\n", - error / 10, error % 10); + rate_error / 10, rate_error % 10); return -EDOM; } else { dev_warn(dev->dev.parent, "bitrate error %ld.%ld%%\n", - error / 10, error % 10); + rate_error / 10, rate_error % 10); } } -- 1.7.1 _______________________________________________ Socketcan-core mailing list [email protected] https://lists.berlios.de/mailman/listinfo/socketcan-core
