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Date: Wed, 18 Jan 2012 12:45:23 +0800
From: realmz paranoid <realmz6@...il.com>
To: Marc Kleine-Budde <mkl@...gutronix.de>
Cc: Wolfgang Grandegger <wg@...ndegger.com>,
"linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
Netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] socket-can: bit-timing calculation
Hi Marc,
On Tue, Jan 17, 2012 at 10:34 PM, Marc Kleine-Budde <mkl@...gutronix.de> wrote:
> Hello,
>
> Realmz Paranoid, a hint from David Miller:
>> Nobody is seeing any of your postings because of "open list: NETWORKING
>> DRIVERS" stuff in the email headers.
>
> On 01/17/2012 11:25 AM, Marc Kleine-Budde wrote:
>> On 01/17/2012 11:18 AM, realmz paranoid wrote:
>> [...]
>>
>>>>>> This is worse because it does not find the best match. The first
>>>>>> match might not be the best.
>>>>>>
>>>>>> I got it, because the tseg1_max and tseg2_max limit, the first found
>>>> best
>>>>> error will not get the best sample point on some hardware.
>>>>> So I'd tweak the blackfin can code.
>>>>
>>>> The algorithm does *not* work well for all configs, especially when the
>>>> clock frequency is not a multiple of 8 MHz. Instead of tweaking the
>>>> algorithm just for your hardware it does make more sense to provide the
>>>> parameters manually using "tq= ...". Also setting "sjw > 1" helps if the
>>>> bit-timing is not optimal.
>>
>> I've an improved version (somewhere) that minimizes sample point error,
>> too. Give me some minutes to find it.
>
> Here it is. Wolfgang wrote the can-calc-bit-timing tool, which he used to generate
> the table in the other mail. It's part of can-utils. I've pushed my improvement
> to my repo (better-bitrate-calculation branch):
>
> https://gitorious.org/~bet-frogger/linux-can/mkl-can-utils
>
> Here's the patch:
>
> From 4df04420f128ec326e536fe55fc819b893a5c9ef Mon Sep 17 00:00:00 2001
> From: Marc Kleine-Budde <mkl@...gutronix.de>
> Date: Sat, 15 May 2010 18:26:03 +0200
> Subject: [PATCH] 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 <mkl@...gutronix.de>
> ---
> 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 f8c04ba..27bf41d 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 <wg@...ndegger.com>
> + * Copyright (C) 2010 Marc Kleine-Budde <mkl@...gutronix.de>
> *
> * Derived from:
> * can_baud.c - CAN baudrate calculation
> @@ -372,18 +373,17 @@ 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);
> }
> @@ -391,11 +391,15 @@ 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)
> @@ -417,48 +421,51 @@ 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);
> }
> }
> -- 1.7.4.1
>
I added bfin-can to can-calc-bit-timing.c and tried with your
better-bitrate-calculation branch, it did improve the sample error.
Thank you.
Here's the result:
Bit timing parameters for bfin-can with 131.250000 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 251 1 1 1 1 33 994318 0.6% 75.0% 75.0% 0.0%
clock 0x00000020 timing 0x00000001
800000 312 1 1 1 1 41 800304 0.0% 80.0% 75.0% 6.2%
clock 0x00000028 timing 0x00000001
- 500000 502 1 1 1 1 66 497159 0.6% 87.5% 75.0% 14.3%
clock 0x00000041 timing 0x00000001
+ 500000 251 3 3 1 1 33 497159 0.6% 87.5% 87.5% 0.0%
clock 0x00000020 timing 0x00000005
250000 266 6 6 2 1 35 250000 0.0% 87.5% 86.6% 1.0%
clock 0x00000022 timing 0x0000001b
125000 533 6 6 2 1 70 125000 0.0% 87.5% 86.6% 1.0%
clock 0x00000045 timing 0x0000001b
- 100000 2499 1 1 1 1 328 100038 0.0% 87.5% 75.0% 14.3%
clock 0x00000147 timing 0x00000001
+ 100000 1249 3 3 1 1 164 100038 0.0% 87.5% 87.5% 0.0%
clock 0x000000a3 timing 0x00000005
50000 1333 6 6 2 1 175 50000 0.0% 87.5% 86.6% 1.0%
clock 0x000000ae timing 0x0000001b
20000 2940 6 7 3 1 386 20001 0.0% 87.5% 82.3% 5.9%
clock 0x00000181 timing 0x0000002c
10000 6666 6 6 2 1 875 10000 0.0% 87.5% 86.6% 1.0%
clock 0x0000036a timing 0x0000001b
@@ -15,7 +15,7 @@
Bit timing parameters for bfin-can with 125.000000 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 40 8 8 8 1 5 1000000 0.0% 75.0% 68.0% 9.3%
clock 0x00000004 timing 0x0000007f
- 800000 312 1 1 1 1 39 801282 0.2% 80.0% 75.0% 6.2%
clock 0x00000026 timing 0x00000001
+ 800000 96 4 5 3 1 12 801282 0.2% 80.0% 76.9% 3.9%
clock 0x0000000b timing 0x00000028
500000 400 1 2 1 1 50 500000 0.0% 87.5% 80.0% 8.6%
clock 0x00000031 timing 0x00000002
250000 200 8 8 3 1 25 250000 0.0% 87.5% 85.0% 2.9%
clock 0x00000018 timing 0x0000002f
125000 1000 3 3 1 1 125 125000 0.0% 87.5% 87.5% 0.0%
clock 0x0000007c timing 0x00000005
-steven
> --
> Pengutronix e.K. | Marc Kleine-Budde |
> Industrial Linux Solutions | Phone: +49-231-2826-924 |
> Vertretung West/Dortmund | Fax: +49-5121-206917-5555 |
> Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |
>
>
>
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