From: Dong Aisheng <b29396@freescale.com>
To: Oliver Hartkopp <socketcan@hartkopp.net>
Cc: Marc Kleine-Budde <mkl@pengutronix.de>,
linux-can@vger.kernel.org, wg@grandegger.com,
varkabhadram@gmail.com, netdev@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: M_CAN message RAM initialization AppNote - was: Re: [PATCH V3 3/3] can: m_can: workaround for transmit data less than 4 bytes
Date: Thu, 6 Nov 2014 09:57:17 +0800 [thread overview]
Message-ID: <20141106015716.GB7642@shlinux1.ap.freescale.net> (raw)
In-Reply-To: <545A692E.40002@hartkopp.net>
On Wed, Nov 05, 2014 at 07:15:10PM +0100, Oliver Hartkopp wrote:
> Hi all,
>
> just to close this application note relevant point ...
>
> I got an answer from Florian Hartwich (Mr. CAN) from Bosch regarding
> the bit error detection found by Dong Aisheng.
>
> The relevant interrupts IR.BEU or IR.BEC monitor the message RAM:
>
> Bit 21 BEU: Bit Error Uncorrected
> Message RAM bit error detected, uncorrected. Controlled by input
> signal m_can_aeim_berr[1] generated by an optional external parity /
> ECC logic attached to the Message RAM. An uncorrected Message RAM
> bit error sets CCCR.INIT to ‘1’. This is done to avoid transmission
> of corrupted data.
>
> 0= No bit error detected when reading from Message RAM
> 1= Bit error detected, uncorrected (e.g. parity logic)
>
> Bit 20 BEC: Bit Error Corrected
> Message RAM bit error detected and corrected. Controlled by input
> signal m_can_aeim_berr[0] generated by an optional external parity /
> ECC logic attached to the Message RAM.
>
> 0= No bit error detected when reading from Message RAM
> 1= Bit error detected and corrected (e.g. ECC)
>
> ---
>
> The Message RAM is usually equipped with a parity or ECC functionality.
> But RAM cells suffer a hardware reset and can therefore hold
> arbitrary content at startup - including parity and/or ECC bits.
>
> So when you write only the CAN ID and the first four bytes the last
> four bytes remain untouched. Then the M_CAN starts to read in 32bit
> words from the start of the Tx Message element. So it is very likely
> to trigger the message RAM error when reading the uninitialized
> 32bit word from the last four bytes.
>
> Finally it turns out that an initial writing (with any kind of data)
> to the entire message RAM is mandatory to create valid parity/ECC
> checksums.
>
> That's it.
>
Thanks for sharing this information.
Does it mean this issue is related to the nature of Message RAM and is
supposed to exist on all M_CAN IP versions?
> Regards,
> Oliver
>
Regards
Dong Aisheng
next prev parent reply other threads:[~2014-11-06 2:27 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-05 13:16 [PATCH V3 1/3] can: add can_is_canfd_skb() API Dong Aisheng
2014-11-05 13:16 ` [PATCH V3 2/3] can: m_can: update to support CAN FD features Dong Aisheng
2014-11-05 14:31 ` Marc Kleine-Budde
2014-11-05 14:42 ` Oliver Hartkopp
2014-11-05 13:16 ` [PATCH V3 3/3] can: m_can: workaround for transmit data less than 4 bytes Dong Aisheng
2014-11-05 14:29 ` Marc Kleine-Budde
2014-11-05 18:15 ` M_CAN message RAM initialization AppNote - was: " Oliver Hartkopp
2014-11-06 1:57 ` Dong Aisheng [this message]
2014-11-06 7:04 ` Oliver Hartkopp
2014-11-06 8:09 ` Dong Aisheng
2014-11-06 12:33 ` Oliver Hartkopp
2014-11-06 12:47 ` Marc Kleine-Budde
[not found] ` <545BA039.7080108@hartkopp.net>
2014-11-07 8:15 ` Dong Aisheng
2015-02-05 19:04 ` new M_CAN IP rev 3.2.x documentation available - was: Re: M_CAN message RAM initialization AppNote Oliver Hartkopp
2014-11-07 8:40 ` M_CAN message RAM initialization AppNote - was: Re: [PATCH V3 3/3] can: m_can: workaround for transmit data less than 4 bytes Dong Aisheng
2014-11-07 8:34 ` Dong Aisheng
2014-11-06 9:00 ` Marc Kleine-Budde
2014-11-05 16:22 ` [PATCH V3 1/3] can: add can_is_canfd_skb() API Eric Dumazet
2014-11-05 17:33 ` Oliver Hartkopp
2014-11-06 1:52 ` Dong Aisheng
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