Date: Fri, 25 Nov 2016 09:07:34 -0800 (PST) From: "Rodney W. Grimes" <freebsd-rwg@pdx.rh.CN85.dnsmgr.net> To: Ian Lepore <ian@freebsd.org> Cc: Hal Murray <hmurray@megapathdsl.net>, freebsd-arm@freebsd.org, Michael Sperber <sperber@deinprogramm.de> Subject: Re: Can't get 11.0-RELEASE to boot on Banana PI M3 Message-ID: <201611251707.uAPH7Y4K022170@pdx.rh.CN85.dnsmgr.net> In-Reply-To: <1480092564.1889.70.camel@freebsd.org>
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[ 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. 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. > > 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. -- Rod Grimes rgrimes@freebsd.org
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