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Re: MCU mimicking a SPI flash slave

From David Brown <david.brown@hesbynett.no>
Newsgroups comp.arch.embedded
Subject Re: MCU mimicking a SPI flash slave
Date 2017-06-15 14:20 +0200
Organization A noiseless patient Spider
Message-ID <ohttrn$nf0$1@dont-email.me> (permalink)
References (2 earlier) <9Eq0B.74561$7A4.41458@fx19.am4> <ohtena$7s5$1@dont-email.me> <gLr0B.74079$O06.57510@fx43.am4> <ohtpct$91f$1@dont-email.me> <Deu0B.62929$z%2.11532@fx27.am4>

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On 15/06/17 13:31, Tom Gardner wrote:
> On 15/06/17 12:04, David Brown wrote:
>> On 15/06/17 10:41, Tom Gardner wrote:
>>> On 15/06/17 09:02, David Brown wrote:
<snip>
>> I think XMOS should go further, and include hardware peripherals for
>> common features - in particular, UARTs, I2C, SPI, timers.  A simple
>> hardware UART peripheral is a small and easy part to make in a chip
>> design.  With the XMOS, you can do it in software - you can write a
>> nice, clear UART software block, without much coding space.  But it
>> takes two hardware threads - a quarter of your chip's power if you have
>> a small device.  Turned into cash, that's about $2 for a UART.  On a
>> chip microcontroller, you have lots of UARTs and they don't take
>> significant resources - it's a "cost" of perhaps $0.02.  For peripherals
>> that you often need, it is /much/ cheaper to have dedicated hardware
>> than to have them in software.
> 
> Hmmm. I understand why you are saying that, but
> dayOfWeek%2==1, so I'll disagree. The questions
> with such peripherals are:
> - where do you stop
> - switch matrix connections
> - apis
> The last is an extra learning curve, especially
> w.r.t. configuration.
> 

I am not sure you really /are/ disagreeing - because I agree that there
is a balance here, and "where do you stop?" is an important question.

The answer is somewhere between "I use this peripheral a lot, it is
cheap in hardware but expensive in software" and "I use this peripheral
occasionally, it is expensive in hardware but cheap in software".  I.e.,
no, there is no clear dividing point, and different developers will have
wildly different opinions.  And different hardware designers have had
different opinions too - from FPGA, through XMOS, PSoC, 68332/MPC5xxx
with TPUs, to microcontrollers with configurable pin selections.  A
common theme is that while the more flexible systems let you make
marvellously complicated peripherals that fit just right for a
specialised need, most of the time they are used for simple UARTs, SPI,
timers with capture or PWM, etc., and they are mostly very inefficient
for those uses.

And I agree that a simple peripheral is easier to use than a complicated
one, and gives an easier interface.  So if you want an 11-bit UART, and
you have an XMOS UART, it is an easy matter to change the
"NUMBER_OF_BITS" from 8 in the sample code to 11.  But a hardware UART
that is that flexible is likely to have scores of pages of register
definitions to wade through to find the right options.

> 
>>> XMOS does provide some techniques (e.g. composable
>>> and interfaces) to reduce the sharpness of the cliffs,
>>> but not to eliminate them. But then the same is true
>>> of ARM+RTOS etc etc.
>>
>> Yes, there are learning curves everywhere.  And scope for getting things
>> wrong :-)  XMOS gives a different balance amongst many of the challenges
>> facing designers - it is better in some ways, worse in other ways.
> 
> Agreed. Horses for courses.
> 
> I feel comfortable with XMOS for bit-banging, DSP and
> similar. I am unclear about having non-trivial ethernet
> protocol stacks and similar.
> 
> 
> 
>>>> Yes, CSP is a great tool.  I was taught it by some of the folks behind
>>>> it.  (Tony Hoare himself was head of the department, but I didn't have
>>>> him as a lecturer.)
>>>
>>> My only contact with him was via his Elliott 803
>>> Algol-60 compiler - and thanking him for it ~30
>>> years later :)
>>
>> At the end of my degree course, I had the chance to stay and do a
>> doctorate with Professor Hoare as one of my supervisors.  But I choose
>> to emigrate to Norway, get married, and try to find a job.  It was the
>> right choice.
> 
> Curiously I made similar choices, although the
> University (Southampton) and destination were
> different.

When you are the kind of nerd that is likely to end up in an ivory tower
doing all your "programming" as symbolic manipulation on a blackboard,
you don't let the chance of a lifetime with a good woman pass you by!

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Thread

MCU mimicking a SPI flash slave John Speth <johnspeth@yahoo.com> - 2017-06-14 10:44 -0700
  Re: MCU mimicking a SPI flash slave Don Y <blockedofcourse@foo.invalid> - 2017-06-14 16:30 -0700
  Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-14 21:54 -0400
    Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-15 08:01 +0100
      Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-15 12:13 -0400
        Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-15 18:01 +0100
          Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-15 16:52 -0400
            Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-15 23:37 +0200
              Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-15 18:15 -0400
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-16 09:25 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-16 13:52 -0400
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-18 22:56 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-19 00:21 -0400
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-19 09:02 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-19 08:36 -0400
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-19 14:47 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-19 09:23 -0400
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-19 15:34 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-20 00:16 -0400
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-20 09:49 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-20 22:44 -0400
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-21 12:10 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-21 12:40 -0400
                Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-21 18:19 +0100
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-21 14:34 -0400
                Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-21 21:41 +0100
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-21 17:14 -0400
                Re: MCU mimicking a SPI flash slave edward.ming.lee@gmail.com - 2017-06-21 13:54 -0700
            Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-15 23:33 +0100
              Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-15 23:12 -0400
                Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-16 07:05 +0100
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-16 02:27 -0400
  Re: MCU mimicking a SPI flash slave Tim Wescott <seemywebsite@myfooter.really> - 2017-06-14 23:17 -0500
  Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-15 08:03 +0100
  Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-15 09:14 +0200
    Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-15 08:25 +0100
      Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-15 10:02 +0200
        Re: MCU mimicking a SPI flash slave Reinhardt Behm <rbehm@hushmail.com> - 2017-06-15 16:25 +0800
          Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-15 10:32 +0200
            Re: MCU mimicking a SPI flash slave Reinhardt Behm <rbehm@hushmail.com> - 2017-06-15 21:48 +0800
          Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-15 10:09 +0100
        Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-15 09:41 +0100
          Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-15 13:04 +0200
            Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-15 12:31 +0100
              Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-15 14:20 +0200
            Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-15 17:46 -0400
              Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-16 13:21 +0200
                Re: MCU mimicking a SPI flash slave stephen@mpeforth.com (Stephen Pelc) - 2017-06-16 13:55 +0000
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-16 16:34 +0200
                Re: MCU mimicking a SPI flash slave stephen@mpeforth.com (Stephen Pelc) - 2017-06-16 15:40 +0000
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-19 00:47 +0200
                Re: MCU mimicking a SPI flash slave stephen@mpeforth.com (Stephen Pelc) - 2017-06-21 15:47 +0000
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-21 19:15 +0200
                Re: MCU mimicking a SPI flash slave stephen@mpeforth.com (Stephen Pelc) - 2017-06-21 15:50 +0000
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-21 19:16 +0200
                Re: MCU mimicking a SPI flash slave stephen@mpeforth.com (Stephen Pelc) - 2017-06-21 18:00 +0000
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-22 11:24 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-22 12:12 -0400
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-16 14:22 -0400
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-19 03:15 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-19 00:54 -0400
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-19 10:30 +0200
                Re: MCU mimicking a SPI flash slave albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-06-19 12:54 +0200
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-19 13:49 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-19 09:28 -0400
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-19 09:19 -0400
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-19 16:23 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-19 23:57 -0400
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-20 12:36 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-20 08:20 -0400
                Re: MCU mimicking a SPI flash slave anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-06-19 14:44 +0000
                Re: MCU mimicking a SPI flash slave albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-06-19 21:39 +0200
                Re: MCU mimicking a SPI flash slave Cecil Bayona <cbayona@cbayona.com> - 2017-06-19 14:59 -0500
                Re: MCU mimicking a SPI flash slave albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-06-20 09:25 +0200
                Re: MCU mimicking a SPI flash slave Cecil Bayona <cbayona@cbayona.com> - 2017-06-20 11:50 -0500
                Re: MCU mimicking a SPI flash slave anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-06-20 12:37 +0000
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-19 22:59 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-20 00:12 -0400
                Re: MCU mimicking a SPI flash slave Dimiter_Popoff <dp@tgi-sci.com> - 2017-06-20 10:25 +0300
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-20 10:44 +0200
                Re: MCU mimicking a SPI flash slave dp <dp@tgi-sci.com> - 2017-06-20 02:36 -0700
                Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-20 11:25 +0100
                Re: MCU mimicking a SPI flash slave Dimiter_Popoff <dp@tgi-sci.com> - 2017-06-20 13:49 +0300
                Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-20 12:54 +0100
                Re: MCU mimicking a SPI flash slave Dimiter_Popoff <dp@tgi-sci.com> - 2017-06-20 16:09 +0300
                Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-20 15:24 +0100
                Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-20 17:46 +0100
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-20 22:28 +0200
                Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-21 00:58 +0100
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-21 13:08 +0200
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-20 16:28 +0200
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-20 12:58 +0200
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-20 12:57 +0200
                Re: MCU mimicking a SPI flash slave Dimiter_Popoff <dp@tgi-sci.com> - 2017-06-20 14:19 +0300
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-20 16:19 +0200
                Re: MCU mimicking a SPI flash slave anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-06-20 12:12 +0000
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-20 16:48 +0200
                Re: MCU mimicking a SPI flash slave Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2017-06-20 21:16 +0100
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-20 23:15 +0200
                Re: MCU mimicking a SPI flash slave Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2017-06-21 07:30 +0100
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-21 12:54 -0400
                Re: MCU mimicking a SPI flash slave David Brown <david.brown@hesbynett.no> - 2017-06-21 19:29 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-21 15:05 -0400
                Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-21 21:34 +0100
                Re: MCU mimicking a SPI flash slave "Elizabeth D. Rather" <erather@forth.com> - 2017-06-21 18:04 -1000
                Re: MCU mimicking a SPI flash slave albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-06-22 10:26 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-22 11:56 -0400
                Re: MCU mimicking a SPI flash slave stephen@mpeforth.com (Stephen Pelc) - 2017-06-22 09:20 +0000
                Re: MCU mimicking a SPI flash slave Wasell <from_usenet@wasell.eu> - 2017-06-22 14:02 +0200
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-22 11:59 -0400
                Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-22 11:58 -0400
                Re: MCU mimicking a SPI flash slave anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-06-22 08:19 +0000
                Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-19 09:53 +0100
        Re: MCU mimicking a SPI flash slave Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-06-15 10:16 +0100
  Re: MCU mimicking a SPI flash slave John Speth <johnspeth@yahoo.com> - 2017-06-15 13:56 -0700
    Re: MCU mimicking a SPI flash slave Don Y <blockedofcourse@foo.invalid> - 2017-06-15 14:41 -0700
      Re: MCU mimicking a SPI flash slave John Speth <johnspeth@yahoo.com> - 2017-06-15 15:08 -0700
        Re: MCU mimicking a SPI flash slave Don Y <blockedofcourse@foo.invalid> - 2017-06-16 11:34 -0700
    Re: MCU mimicking a SPI flash slave rickman <gnuarm@gmail.com> - 2017-06-15 18:20 -0400
    Re: MCU mimicking a SPI flash slave edward.ming.lee@gmail.com - 2017-06-21 07:58 -0700
  Re: MCU mimicking a SPI flash slave Walter Banks <walter@bytecraft.com> - 2017-06-19 12:23 -0400

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