Date: Mon, 20 Dec 2021 10:48:38 +1100 From: MJ <mafsys1234@gmail.com> Cc: freebsd-arm@freebsd.org Subject: Re: Dealing with slow USB disks, was: Re: Saving environment variables in u-boot Message-ID: <b0fbd30e-53f9-fe72-568d-1cd368e76285@gmail.com> In-Reply-To: <1387CAB3-CFE7-4C47-8A9C-24D6E56D8C3C@yahoo.com> References: <20211217013613.GA4452@www.zefox.net> <E2F6D50B-694A-4108-BD84-C85BC96AD832@yahoo.com> <20211218005946.GA7670@www.zefox.net> <5C44D0E6-2FF1-4EEB-B21A-83333D6FCF46@yahoo.com> <9D416106-660F-40BB-98D2-1354B53D2FEF@yahoo.com> <EC6CC83C-BC0A-4A12-866A-9FA24083FF7E@yahoo.com> <20211218223543.GA9484@www.zefox.net> <6105a8a6-e760-2183-72fd-92e5a60aa8df@gmail.com> <20211219005134.GA12292@www.zefox.net> <4910504f-3051-9a95-d8e4-95434042196d@gmail.com> <20211219161816.GA14873@www.zefox.net> <6edfdb4a-8ed3-7ef3-c3b2-7d2d7fd3206c@gmail.com> <1387CAB3-CFE7-4C47-8A9C-24D6E56D8C3C@yahoo.com>
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On 20/12/2021 9:55 am, Mark Millard wrote: > On 2021-Dec-19, at 13:39, MJ <mafsys1234@gmail.com> wrote: > >> On 20/12/2021 3:18 am, bob prohaska wrote: >>> On Sun, Dec 19, 2021 at 10:03:47PM +1100, MJ wrote: >>>> >>>> I would think a mechanical USB is going to pull a "lot" of power when beginning spin-up, but once rotating should be easily powered by a USB hub. Though this would not explain how it works on RPI4 unless the powered hub you're using is USB2. >>>> >>> That's what I thought too. I certainly didn't expect the disk to work >>> without a powered hub. The Pi4 is a different animal; it has USB3 ports >>> and more power available. That the mechanical disk works at all on the >>> Pi3's USB2 ports without assistance is quite surprising. >> >> See here: https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#typical-power-requirements >> It mentions 1.2A, which covers your load, but, I would suspect if you attached, for example, a USB 'thumb' drive or other devices you would cause problems. > > Unfortunately there is more involved: USB2's standard > indicates 500mA (0.5A) at maximum on 1 standard USB2 > port. It takes 2 USB2 ports to get to a total of 1000mA > (1A) (unless a port is designed to go beyond the > standard). To my knowledge most RPi*'s are not designed > to support more than the standard USB2 power on any of > its USB2 ports. (The 3A+, Zero W/WH, and Zero are > apparently exceptions, depending on the power supply > used and such.) You are correct, however, it seems the RPI foundation violates the "standard" and creates their own for Bs: https://raspberrypi.stackexchange.com/questions/51615/raspberry-pi-power-limitations (Section: How much current can be drawn from the USB ports?) M
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