Re: Dealing with slow USB disks, was: Re: Saving environment variables in u-boot
- Reply: Mark Millard via freebsd-arm : "Re: Dealing with slow USB disks, was: Re: Saving environment variables in u-boot"
- In reply to: Mark Millard via freebsd-arm : "Re: Dealing with slow USB disks, was: Re: Saving environment variables in u-boot"
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Date: Sun, 19 Dec 2021 23:48:38 UTC
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