Pi lightweight server with USB SSD instead of powered HDD?

Well I did the research and it seems that what makes the difference is the use of a LAN9514 chip which contains all the Ethernet and 4 x USB circuitry, and carries power limiting circuitry too.

A definite example of creeping featurism...

--
"First, find out who are the people you can not criticise. They are your  
oppressors." 
      - George Orwell

On some models - those with ethernet - it appears that they use a chip (LAN2514) which takes it upon itself to monitor and limit power. Obviously its intended for kit that has limited internal power supplies, but it becomes pointless if you have an external one.

Why they don't bypass its power stuff and feed power straight to the USBs, only some pointy headed Pi designer knows.

I am frankly flabbergasted that such a crap piece of design was incorporated

As an electronic designer I simply didn't believe they could be that stupid.

Apologies to all I offended by doubting them.

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"Nature does not give up the winter because people dislike the cold." 

? Confucius

DRS3000 (Intel) and DRS6000 (SPARC) running Unix. This was in the 1990s. The source code that we bought was written for Intel, and we had to do a *lot* of #ifdefs for SPARC to reverse the byte ordering of multi-byte integers between the format in the packets received and the native format of the CPU.

Would be unusual to mean bit in that context. I can believe a 1984 Z80 based computer to have 64 KiB! They also write "12 Kg" so I don't trust their capitalisation skills.

Interesting: that was after my time on ICL kit. The really odd one for me was 18 months in NYC (1976/77) building an sales and accounting system for a toy manufacturer on a 2903. At that time, although the 2903 was always capable of handling multiple 24x80 green screen terminals, there was no system or skeleton for managing a set of screens accessing a common set of indexed access files, so I designed and built one. Somewhat to my surprise it ran successfully the first time we tried it. FWIW this skeleton was written in PLAN, with the file handler and application code in COBOL. Officially, there was no PLAN assembler on the 2903, so we took a disk to the only 1900 installation in NYC and copied the PLAN3 software and libraries. It was sometimes useful to be hired by ICL!

The last major project I did on ICL kit was at the BBC, building ORPHEUS, the original Radio Three music planning system. That was on a dual 2966 installation, so much bigger than the ex-Tarmac 2966 at NMOC. The project started in 1980, went live in 1982. It was written in COBOL using an IDMSX database.

My last contact with anything connected with ICL was around 1986. By that time I was at Logica - easily the best place I ever worked.

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Martin    | martin at 
Gregorie  | gregorie dot org

Wouldn't that require much wider power rails? Maybe there simply wasn't enough space on the PCB to accommodate that without making the PCB bigger?

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Martin    | martin at 
Gregorie  | gregorie dot org

That might be the case for your Pi, but UNIX/Linux filing system permissions are a lot more flexible than that.

---druck

These are all multilayer boards

--
Truth welcomes investigation because truth knows investigation will lead  
to converts. It is deception that uses all the other techniques.

It was not unusual in some 8 bit micros to have paged RAM and ROM. It made stuff pretty tricky to program tho

--
Truth welcomes investigation because truth knows investigation will lead  
to converts. It is deception that uses all the other techniques.

It's not a crap design, it's deliberate to prevent to prevent damage to both the Pi, who's circuit board is not designed to take high current, and the power supply, which may be some cheap one which may overheat when trying to supply too much current.

If you want large currents use a powered hub, rather than trying to turn the Pi in to a toaster.

---druck

By 1984 paged memory was common on Z80 systems 256K DRAM chips were getting cheap so 256KiB was an easy option, with a little care you could build the board to take either size chip.

--
Steve O'Hara-Smith                          |   Directable Mirror Arrays 
C:\>WIN                                     | A better way to focus the sun 
The computer obeys and wins.                |    licences available see 
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Understood, but are the ground and positive rails duplicated on more than one layer? Or are they significantly wider than signal lines? Its difficult to tell from visual inspection.

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Martin    | martin at 
Gregorie  | gregorie dot org

On Sun, 18 Jul 2021 08:28:38 +0100, The Natural Philosopher declaimed the following:

Partly because the USB spec itself says devices must start in the 100mA mode and negotiate with the host if they want the 500mA load.

""" The limit to device power draw is stated in terms of a unit load which is

100 mA, or 150 mA for SuperSpeed devices. Low-power devices may draw at most 1 unit load, and all devices must act as low-power devices before they are configured. A high-powered device must be configured, after which it may draw up to 5 unit loads (500 mA), or 6 unit loads (900 mA) for SuperSpeed devices, as specified in its configuration (i.e. because the maximum power may not be available).[42][43][44][45] """

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	Wulfraed                 Dennis Lee Bieber         AF6VN 
	wlfraed@ix.netcom.com    http://wlfraed.microdiversity.freeddns.org/

Typically a digital board will have entire layers dedicated to + and ground, but there may not be high-current access to them, only small vias. It's a matter of minimising coupling through the rails rather than supplying lots of current.

I think this issue has been settled by quoting the USB spec. In any case, a Pi isn't a power supply, and any significant current required by a peripheral should be fed directly to it. Using a Pi as a power supply will make it run hotter, an important consideration for a Pi4.

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Joe

The tendency used to be to have ground on top solid as a shield, and another layer was the power supply lines.

But I never designed a surface mount board :-)

signal wiring could then go north south in one layer and east west on another!

--
In a Time of Universal Deceit, Telling the Truth Is a Revolutionary Act. 

- George Orwell

Nice!

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Martin    | martin at 
Gregorie  | gregorie dot org

Maybe I've been lucky, YMMV, etc, but I've had an RPi 3B+ with a WD Elements portable hard drive (no separate power supply) working for several years without any problems that I've noticed.

John

Yes, me too with a Seagate Expansion Portable (2.5" usb powered hdd) before I replaced it with a Pi 4 with ssd. Was my home web server etc. for years, never crashed.

I've only ever done two layers, where that strategy was good for minimising vias.

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Joe