Date: Fri, 25 Nov 2016 10:46:26 -0700 From: Ian Lepore <ian@freebsd.org> To: "Rodney W. Grimes" <freebsd-rwg@pdx.rh.CN85.dnsmgr.net> Cc: Michael Sperber <sperber@deinprogramm.de>, freebsd-arm@freebsd.org Subject: Re: Can't get 11.0-RELEASE to boot on Banana PI M3 Message-ID: <1480095986.1889.76.camel@freebsd.org> In-Reply-To: <201611251707.uAPH7Y4K022170@pdx.rh.CN85.dnsmgr.net> References: <201611251707.uAPH7Y4K022170@pdx.rh.CN85.dnsmgr.net>
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On Fri, 2016-11-25 at 09:07 -0800, Rodney W. Grimes wrote: > [ Charset ISO-8859-1 unsupported, converting... ] > > > > On Fri, 2016-11-25 at 08:42 -0800, Rodney W. Grimes wrote: > > > > > > > > > > > > > > > > > > > sperber@deinprogramm.de said: > > > > > > > > > > > > > > > Ah, thanks ... but that's not standard RS232, right???(BPI > > > > > homepages says > > > > > "TTL".)??If it isn't, what kind of hardware connects to > > > > > that?? > > > > The normal setup for RS232 is that the transmit and receive > > > > signals > > > > come out? > > > > of a big chip (SOC, or PCI UART, or USB UART, or ...) and then > > > > go > > > > through a? > > > > level converter which is typically a MAX-232 or one of many > > > > clones > > > > or? > > > > variants.??The "TTL" is telling you that it doesn't have that > > > > level > > > > converter? > > > > chip. > > > > > > > > You can either add a level converter chip and then plug it into > > > > a > > > > real RS-232? > > > > port, or find some setup that also doesn't have the level > > > > converter > > > > and? > > > > speaks TTL levels.??Adafruit and probably many others sell a > > > > USB > > > > UART without? > > > > the level converter for applications like this. > > > > ? https://www.adafruit.com/product/954 > > > > > > > > Sometimes, TTL means 3V CMOS levels and 5V from real TTL/CMOS > > > > will > > > > fry your? > > > > expensive chip.??Best to check carefully.??The above part says > > > > 3V.??It also? > > > > has an extra power wire that you get to ignore. > > > Be SURE to ignore that extra power wire!??If your USB/Serial > > > adapter > > > also has > > > a power wire DO NOT CONNECT IT.??Many of these embeded boards > > > provide > > > a power > > > pin with the serial interface that can be used to power something > > > external, > > > like a level shifter, and many of the USB/Serial adapters also > > > bring > > > out the > > > USB 5V rail on a wire.??DO NOT CONNECT THE TWO!? > > > > > Ummm... say what? > > > > I power my rpi boards using the 5v power from the USB serial > > adapter > > connected to the 5v pin on the rpi header. ?I can't imagine any > > reason > > not to. > You either have a USB port wiling to supply more than the 500mA > from the standard, or are running your RPI under very light load. > This is NOT the recomended path to power a RPI, and if the RPI is > getting power from the micro usb port your connecting 2 power > supplies in parallel, which is bad. > And why exactly is two sources of +5v a problem (not that I said I was doing that, but I have at times done that, and it works just fine)? > If you plub a USB device into your RPI that draws significant > current it well probably reboot due to power loss. > > For information on how much power your PI wants/needs: > https://www.raspberrypi.org/help/faqs/#powerReqs > > > > > > > > > > That being said, there are many aftermarket USB/Serial cables > > > avaliable, > > > usually a 3.3V version of these well work everywhere as long as > > > it > > > has > > > 5V tolerent inputs, which most of the newer ones do, check the > > > specs > > > from the vendor.??3.3V outputs well satisfy the input > > > requirements of > > > a 5V TTL/CMOS circuit and not cause it problems, the opposite is > > > not > > > always true. > > > > > Usb serial adapter based on Prolific chipsets are NOT 5v tolerant. > > ?Those based on FTDI chips are. ?Those are the two big names in > > usb- > > serial chips, but there are others out there too; you have to check > > the > > datasheet to be sure. > From my read of the Prolific data sheet that is not clear, they > specify > 3.3v and 3.3v 5v tolerent, but then they do not clearly state which > pins are 3.3v and which are 3.3v+5v tolerent. I'll take your word > that they don't like 5V on the serial rx pin. > They are actually very clear that of the IO pins, only the RESET_N pin is 5v tolerant. > > > > > > > > Watch your lead length and wire sizes if you need to do anything > > > funny > > > to get this connected, capacitive loading of any kind on this > > > type of > > > signal can cause character loss, especially at speeds above 9600 > > > baud. > > > > > Ummm... that sounds pretty bogus too, considering that I've run > > ftdi > > chips at 12mbps using breadboards with a rat's nest of wiring to > > carry > > the comms signals to other boards. > Iout of most of these chips is 4mA, you are welcome to do the RC > calculations. You can often get away with amazingly poor setups, > then suddenly get bitten by what looks to be just fine but drops > characters. > > Full level RS-232 specifies cable length of 50ft at 19200, your > not going to get away with that using CMOS 4mA drivers unless > you have very low loss cable. Nice introduction of a red herring. Who said anything about 50 foot cables? Oh wait... you did. Only you. -- Ian
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