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[94.197.200.66]) by smtp.gmail.com with ESMTPSA id b131sm3216418wmb.34.2021.02.26.08.14.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Feb 2021 08:14:35 -0800 (PST) Date: Fri, 26 Feb 2021 16:14:34 +0000 From: Torin Cooper-Bennun To: Marc Kleine-Budde Cc: linux-can@vger.kernel.org Subject: Re: can, tcan4x5x: look to merge rpi support into rpi kernel tree Message-ID: <20210226161434.ymdrmclic6nrccj5@bigthink> References: <20210226121854.4gb5yufb23hyar73@bigthink> <7254df67-202f-ac23-c45c-fcb5172a70a3@pengutronix.de> <20210226123144.cwhjberqeyjctc6w@bigthink> <2aebafa3-6a18-7d14-b32d-e17909d3d6a8@pengutronix.de> <20210226132620.wfuvywkzmhwfmhpc@bigthink> <20210226133936.q3o7hrshyurhj3ke@pengutronix.de> <20210226134522.kd3oxtx3u4ltjxos@bigthink> <20210226140054.725kihkdgkmtl3xf@pengutronix.de> <20210226152633.dkro7ffhye4c72hb@bigthink> <20210226160135.w43onb3z25xhv4re@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210226160135.w43onb3z25xhv4re@pengutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-can@vger.kernel.org On Fri, Feb 26, 2021 at 05:01:35PM +0100, Marc Kleine-Budde wrote: > > Is timestamp-wrapping a concern for rx-offloading? > > No, as long as you provide a proper u32 timestamp, which means wrap > around at 0xffffffff to 0x0. As the tcan4x5x has only a 16 bit > timestamp, shift it to full 32 bit, like this: > > https://elixir.bootlin.com/linux/v5.11/source/drivers/net/can/flexcan.c#L805 > > On the mcp with true 32 bit timestamp there's a wraparound every 107 > seconds at 40 MHz external clock (0xffffffff / 40000000). > > The tcan has the TSS.TCP as a prescaler and increments in bit time, > which is 5MHz max. This results in a wrap around every 13ms (0xffff / > 5000000) with a prescaler of 1. With a prescaler of 16, you can increase > this to 209ms (0xffff / 5000000 * 16), which gives an accuracy of 2 > bytes. Nice, thank you, that all sounds good. I'll get to work. :) -- Regards, Torin Cooper-Bennun Software Engineer | maxiluxsystems.com