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Re: MCU mimicking a SPI flash slave

From rickman <gnuarm@gmail.com>
Newsgroups comp.arch.embedded
Subject Re: MCU mimicking a SPI flash slave
Date 2017-06-15 16:52 -0400
Organization A noiseless patient Spider
Message-ID <ohurrv$bbq$1@dont-email.me> (permalink)
References <ohrsl0$1i36$1@gioia.aioe.org> <ohsp5r$79v$1@dont-email.me> <8hq0B.195995$B23.172267@fx37.am4> <ohubh3$a2g$1@dont-email.me> <q3z0B.72490$wG6.62543@fx38.am4>

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Tom Gardner wrote on 6/15/2017 1:01 PM:
> On 15/06/17 17:13, rickman wrote:
>> Tom Gardner wrote on 6/15/2017 3:01 AM:
>>> On 15/06/17 02:54, rickman wrote:
>>>> John Speth wrote on 6/14/2017 1:44 PM:
>>>>> Hi folks-
>>>>>
>>>>> I'm hoping to tap into your various experiences to see if what I'm
>>>>> thinking
>>>>> is practical.
>>>>>
>>>>> Our customer has a device into which a Datakey is plugged to extract data
>>>>> stored in the device.  The Datakey is a really just a trade name for a SPI
>>>>> flash with ergonomic features that resemble a real key (see datakey.com).
>>>>> Our customer would like to replace the Datakey with a new design that will
>>>>> transmit the data wirelessly instead of storing it to the Datakey SPI
>>>>> flash.
>>>>>
>>>>> We're proposing a design based on an MCU which will appear as a SPI slave
>>>>> flash device, store the data pumped to it from the customer's device, and
>>>>> forward it wirelessly.  I'm wondering if it's practical to accomplish it.
>>>>> The firmware would have to be totally responsive temporally and in data
>>>>> content.  That sounds like a tough hill to climb that requires getting the
>>>>> interface just right, nearly perfect.  I see a lot of pitfalls that could
>>>>> make the effort a dead end.
>>>>>
>>>>> Does anybody have any success or failure stories to relate that would help
>>>>> us gauge the feasibility of the proposed design?
>>>>
>>>> I have no experience in building such a product, but why not use an actual
>>>> SPI
>>>> data flash as the intermediate storage while the MCU monitors the action
>>>> and
>>>> forwards the data?  This would require periods when the MCU could read the
>>>> data
>>>> flash.  Is that possible or practical?
>>>>
>>>> I had a design that needed a 30 MHz SPI like interface (not entirely
>>>> compatible
>>>> though) which was designed to read/write registers.  I considered using a
>>>> fast
>>>> CPU to emulate the interface in software, but it just couldn't meet the
>>>> timing.
>>>> Even with a 700 MIPS processor I wasn't sure it could receive the
>>>> command to
>>>> read a register and then get the data onto the output fast enough.  I'm
>>>> not sure
>>>> of the timing of the SPI interface you have, but it will likely be hard to
>>>> emulate the SPI in software.
>>>
>>> That sounds easy for the XMOS processors:
>>>  - multicore (up to 32 100MIPS cores)
>>>  - FPGA-like i/o, e.g. SERDES, buffers, programmable
>>>    clocks to 250Mb/s, separate timer for each port
>>>  - i/o timing changes can be specified/measured in
>>>    software with 4ns resolution
>>>  - guaranteed latencies <100ns
>>>  - *excellent* programming model based on CSP
>>>    (summary: of "Occam in C")
>>>  - Eclipse-based dev environment
>>
>> Any yet the XMOS can't run fast enough to return a result in the time
>> available.  What a pity, all dressed up an nowhere to go.
>
> You'll have to explain that, because I don't understand
> what you are referring to.

Maybe I don't understand the speed of the XMOS.  Nothing you write above 
says to me it is any faster than the 700 MIPS processor I considered. 
Nothing written above would allow it to perform the task any differently 
than the bit banging approach I initially considered.

So what are you confused about?

Maybe you don't understand the problem.  A bit serial data port (two bits 
wide actually, but that is not relevant) provides data, address and a two 
bit command word serially.  The last bit of the command work is indicated by 
a "command" signal going high during that bit.  Data is clocked in on the 
rising edge of the clock.  When the command word is a read, the read data is 
provided serially starting on the subsequent falling edge.  This provides 15 
ns from rising edge to falling edge.  It is possible to prefetch the read 
data based on the shifted address on each rising edge until the command 
signal is asserted.  This helps with timing of the memory fetch, but still, 
that data has to be presented to the serial port output in 15 ns and updated 
every 30 ns.

I'd like to see code that will make this work.  Or maybe you weren't 
addressing my previous application?  For the OP, can the XMOS emulate a 30 
Mbps SPI port?


>>> Currently I'm managing to count transitions in
>>> software on two 50Mb/s inputs, plus do
>>> simultaneous USB comms to a host computer.
>>
>> Can you output a result before the next input transition?
>
> Yes and no.
>
> Yes: the output (to a host processor and/or LCD)
> proceeds in parallel with the next capture phase.

I'm referring to bit I/O using the same 50 MHz clock.


> No: in the current incarnation there is a short gap
> between capture phases as the results are passed
> from one core to another and the next capture phase
> is started. While it isn't important in my application,
> I may be able to remove that limitation in future
> incarnations.

That's a lot more than a "short" gap in the context of a fast clock.


>>> Processors plus £10 devkit available from Farnell
>>> and DigiKey.
>>
>> Not a very good processor to use in cost conscious applications.  The lowest
>> price at Digikey is $3 at qty 1000.  They can't make a part in the sub-dollar
>> range?
>
> Don't presume everybody has your constraints.

I don't, but not everyone has *your* constraints.  If a processor can't be 
sold in a low cost product, it cuts off the largest volume parts of the 
market including the app I am looking at presently.

-- 

Rick C

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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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