Date: Sat, 06 Jan 2018 15:23:51 -0700 From: Ian Lepore <ian@freebsd.org> To: "Rodney W. Grimes" <freebsd-rwg@pdx.rh.CN85.dnsmgr.net>, Mark Millard <markmi@dsl-only.net> Cc: Mark Linimon <linimon@lonesome.com>, Freebsd-arm <freebsd-arm@freebsd.org> Subject: Re: I now have access to a Rock64-4GB (Rock64_V2.0 board); I hope to put FreeBSD on it someday Message-ID: <1515277431.1865.20.camel@freebsd.org> In-Reply-To: <201801062158.w06LwbY1013783@pdx.rh.CN85.dnsmgr.net> References: <201801062158.w06LwbY1013783@pdx.rh.CN85.dnsmgr.net>
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On Sat, 2018-01-06 at 13:58 -0800, Rodney W. Grimes wrote: > > > > On 2018-Jan-6, at 8:45 AM, Emmanuel Vadot <manu at > > bidouilliste.com> wrote: > > > > > > > > On 2018-01-06 17:43, Emmanuel Vadot wrote: > > > > > > > > On 2018-01-05 15:45, Mark Linimon wrote: > > > > > > > > > > On Fri, Jan 05, 2018 at 06:27:41AM -0800, Mark Millard wrote: > > > > > > > > > > > > the early boot baudrate for the console is apparently > > > > > > 1.5Mbit/s > > > > > I've had to use minicom. That's the only thing that I'm sure > > > > > supports it. > > > > > mcl > > > > Works fine with tip(1) here using an FDTI usb<->serial, using a > > > > PL2303XA doesn't work (but should based on the datasheet), and > > > > my > > > > CP2108 should work but I haven't tested yet. > > > Also my PL2303XA adapter works on linux using minicom but only > > > for RX, that might be a driver issue. > > I've been using Serial on an old MacOS X laptop. > > I've done more experiments. Here is what I've > > observed. . . > > > > For a CH340G, Serial did not allow 1500000 > > (built-in driver for USB ID 1a86:7523:0254) > > but Serial is being updated to allow it. (I > > have a preliminary release now, so I have > > 1500000 support now.) > I have to seriously laugh at the idea of doing > TTL serial ports at 1.5MHz down unbalanced, > unterminated single end wires. Just not a > reliable way to communicate. > I've validated ftdi<->ftdi and ftdi<->imx6-uart at 3.3v ttl level over 24ga jumper wires about 20 inches long at 4mpbs. Purposely not a good signal environment, just bare jumpers strung across my desk. I've also tested transfers between pairs of good-quality end-user type usb-serial adapters connected with a null modem adapter at 2mbps; those connections amounted to a couple meters of wire, but they were at rs232 line level. I've never found adapters that can go faster than 2mpbs, because of the cheap ttl<->rs232 chips they contain (most of them max out around 1mbps). > Hopefully your doing this at 5V, at least > then you have a good noise margin, at 3.3V > you lose another 33% of that. > > Also most of these USB/232 adapters have no > way to do flow control, so you better have > a darn big fifo or your host usb stack better > be darn fast at getting data off the chip. > Modern ftdi chips have 2K or 4K fifo. I would expect other modern ubs- serial chips to have similarly big fifos, but even the older ones all had 256 or 384 bytes. And on a usb 2.0 bus it can empty out 512b every 125us. -- Ian
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