linux-kernel - Re: [PATCH v2 0/5] minitty: a minimal TTY layer alternative for embedded systems

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Date:   Mon, 3 Apr 2017 21:46:08 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Stuart Longland <stuartl@...glandclan.id.au>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andi Kleen <andi@...stfloor.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 0/5] minitty: a minimal TTY layer alternative for
 embedded systems

On Mon, Apr 3, 2017 at 8:57 PM, Rob Herring <robh@...nel.org> wrote:
> On Mon, Apr 3, 2017 at 1:14 PM, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>> On Mon, Apr 3, 2017 at 12:44 AM, Stuart Longland
>> <stuartl@...glandclan.id.au> wrote:
>>> On 03/04/17 07:41, Nicolas Pitre wrote:
>>>>> No PTYs seems like a big limitation. This means no sshd?
>>>> Again, my ultimate system target is in the sub-megabyte of RAM.  I
>>>> really doubt you'll be able to fit an SSH server in there even if PTYs
>>>> were supported, unless sshd (or dropbear) can be made really tiny.
>>>> Otherwise you most probably have sufficient resources to run the regular
>>>> TTY code.
>>>
>>> Are we talking small microcontrollers here?  The smallest machine in
>>> terms of RAM I ever recall running Linux on was a 386SX/25 MHz with 4MB
>>> RAM, and that had a MMU.
>>
>> Let's halve that. I once tried and ran Linux in 2 MiB, incl. X, twm, and xterm.
>> Of course with swap enabled.  And swapping like hell.
>
> These are different target uses. We're talking about fixed function,
> statically linked user space at the minimum (some may want no
> userspace even). Applications that could use an RTOS instead but
> benefit from the Linux hardware support, features and ecosystem. It's
> not a whole new code base or environment to learn. Maybe Zephyr will
> have traction and improve things, but projects I've been involved with
> using RTOSs generally have discussions around needing to re-write the
> crappy RTOS.

Sure. I just wanted to point out that there was a time you could have
_more_ than you need for small fixed function embedded systems in
2 MiB of RAM.

> The absolute amount of RAM target is not so important. What's
> important is getting to a size feasible for onchip RAM. That's always
> moving (up), but has generally been out of reach for Linux.

DigiKey shows 39 ARM SoCs with 1 MiB or more of RAM.
But once you want 3 MiB or more, the lone winner is Renesas' RZ/A1 (up to
10 MiB).

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds