Re: RP2040 reset idea

From	The Natural Philosopher <tnp@invalid.invalid>
Newsgroups	sci.electronics.design, comp.sys.raspberry-pi
Subject	Re: RP2040 reset idea
Date	2024-09-22 09:33 +0100
Organization	A little, after lunch
Message-ID	<vcokpc$24ol2$6@dont-email.me> (permalink)
References	(9 earlier) <057uejd09fhuk7ktcqljburd969bv3vfdc@4ax.com> <vcn82a$1net1$1@dont-email.me> <l39uejlvspoestr2od47ob2klth3m1bf9u@4ax.com> <vcnbbs$1nt8a$1@dont-email.me> <bqjuej5vjt4urj5ds16hoi7f2n3elts7q9@4ax.com>

Cross-posted to 2 groups.

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On 22/09/2024 00:11, john larkin wrote:
> On Sat, 21 Sep 2024 20:46:52 -0000 (UTC), Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
> 
>> john larkin <JL@gct.com> wrote:
>>> On Sat, 21 Sep 2024 19:50:34 -0000 (UTC), Phil Hobbs
>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>
>>>> john larkin <JL@gct.com> wrote:
>>>>> On Sat, 21 Sep 2024 19:29:26 +0100, The Natural Philosopher
>>>>> <tnp@invalid.invalid> wrote:
>>>>>
>>>>>> On 21/09/2024 16:08, john larkin wrote:
>>>>>>> On Sat, 21 Sep 2024 09:12:06 +0100, The Natural Philosopher
>>>>>>> <tnp@invalid.invalid> wrote:
>>>>>>>
>>>>>>>> On 20/09/2024 19:00, john larkin wrote:
>>>>>>>>> On 20 Sep 2024 11:30:13 +0100 (BST), Theo
>>>>>>>>> <theom+news@chiark.greenend.org.uk> wrote:
>>>>>>>>>
>>>>>>>>>> In comp.sys.raspberry-pi The Natural Philosopher <tnp@invalid.invalid> wrote:
>>>>>>>>>>> On 19/09/2024 23:09, Lasse Langwadt wrote:
>>>>>>>>>>>> On 9/18/24 00:33, john larkin wrote:
>>>>>>>>>>>
>>>>>>>>>>>>> It looks like a USB memory stick. You can delete or add files if you
>>>>>>>>>>>>> want.
>>>>>>>>>>>>>
>>>>>>>>>>>>> It boots CPU 0 (the one we call Alice) from a file with the extension
>>>>>>>>>>>>> .UL2
>>>>>>>>>>>>>
>>>>>>>>>>>>> Why   .UL2   one wonders.
>>>>>>>>>>>>>
>>>>>>>>>>>>> We'll put a bunch of files into the flash. Code for Bob, the 2nd CPU.
>>>>>>>>>>>>> An FPGA bitstream file. A prototype calibration table. A README file
>>>>>>>>>>>>> to explain everything in plain English.
>>>>>>>>>>>>
>>>>>>>>>>>> sure it's not UF2?
>>>>>>>>>>>>
>>>>>>>>>>>> https://github.com/microsoft/uf2
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>> Definitely uf2 here.
>>>>>>>>>>>
>>>>>>>>>>> And no, you cannot 'delete or add files' to it.
>>>>>>>>>>> The action of pretending to download a uf2 file into what appears to be
>>>>>>>>>>> an empty drive, erases everything on it and programs the flash.
>>>>>>>>>>>
>>>>>>>>>>> There are no visible files to delete.
>>>>>>>>>>
>>>>>>>>>> Neat.  So basically you throw some files at it, which causes a series of
>>>>>>>>>> block writes.  UF2 picks out specially tagged block writes and uses that to
>>>>>>>>>> program the flash.  It doesn't actually care what other stuff is written to
>>>>>>>>>> the flash as it ignores all of that, so it doesn't care about all the FAT
>>>>>>>>>> stuff or whatever junk your OS decides to put on there.
>>>>>>>>>>
>>>>>>>>>> Means you can write any kind of files to it and it'll only pay attention to
>>>>>>>>>> the specific tagged blocks.  If the OS is happy to cache the medium (as many
>>>>>>>>>> do) you could maybe even reformat it as some other filesystem like NTFS and
>>>>>>>>>> it would still handle writing the UF2 file correctly.
>>>>>>>>>>
>>>>>>>>>> Theo
>>>>>>>>>
>>>>>>>>> My Pi guy says that you can only write one file, and the act of
>>>>>>>>> writing that file wipes anything that was there before. So the flash
>>>>>>>>> probably doesn't have a file structure, and the USB memory-stick write
>>>>>>>>> is, well, a sort of cheap trick.
>>>>>>>>>
>>>>>>>>> That's workable, if inelegant. We can pack everything we need into
>>>>>>>>> that one big file and users can upgrade box code in the field pretty
>>>>>>>>> easily.
>>>>>>>>>
>>>>>>>>
>>>>>>>> It gets nastier if you want to preserve config info across reboots.
>>>>>>>> It is possible to read and write areas of flash from the code, but its
>>>>>>>> no picnic.
>>>>>>>> And it gets wiped when new code is uploaded
>>>>>>>>
>>>>>>>>
>>>>>>>> It is an area I will have to tackle for one project tho.
>>>>>>>
>>>>>>> Yes, writing to flash from the running application is nasty.
>>>>>>>
>>>>>>> We have to calibrate each box. We'll store the prototype calibration
>>>>>>> table inside the big flash image. At factory test, we'll grab that,
>>>>>>> edit it for this particular unit, and save it to a small SPI eeprom
>>>>>>> chip. That costs 24 cents and one chip select pin.
>>>>>>>
>>>>>>> My guy says that there are a few magic integers at the start of the
>>>>>>> UF2 file that identifies it, well, as a UF2 file. That confirms that
>>>>>>> the Pico flash doesn't have a file structure, it just stores one giant
>>>>>>> chunk of stuff starting at the start.
>>>>>>>
>>>>>>> It's Windows who lies about it acting like a USB memory stick that
>>>>>>> stores files.
>>>>>>>
>>>>>>> We did consider saving the real cal table at some fixed physical
>>>>>>> address near the end of the flash , on the theory that nobody will
>>>>>>> ever write a bootable image that big. That might work.
>>>>>>>
>>>>>> That seems to be the case.
>>>>>>
>>>>>> I looked into it enough to see that it would be possible to store NV
>>>>>> data in a high part of the flash.
>>>>>>
>>>>>> I think that the runtime provides access to a memory location that
>>>>>> indicates the end of the uploaded flash image, so in theory flash above
>>>>>> that is free to write, with the proviso it has to be done in large
>>>>>> blocks on specific address boundaries.
>>>>>>
>>>>>> All this is at least Pi Pico specific anyway.
>>>>>
>>>>> We're using the RP2040 chip, so will have a huge flash chip. We will
>>>>> sometimes store an FPGA config file that could be too big for the 2
>>>>> MByte part on the Pico.
>>>>>
>>>>>
>>>>>>
>>>>>> Will keep me busy through the dark winter days...:-)
>>>>>
>>>>> Storing anything in high flash still has the problem that you can't
>>>>> run flash-cached code while the write is going on, unless you are very
>>>>> careful.
>>>>>
>>>>>
>>>>
>>>> It?s good to have a warm relationship with your linker mapfile. ;)
>>>>
>>>> Cheers
>>>>
>>>> Phil Hobbs
>>>
>>> Interrupts might get nasty, demanding swaps into the flash cache when
>>> the flash is busy writing.
>>>
>>>
>>
>> That’s where the mapfile comes in. Assuming that you can update one flash
>> page while updating another, that is.
>>
>> Cheers
>>
>> Phil Hobbs
> 
> The RP2040 usually executes code out of a small 16 Kbyte sram that
> caches code from the flash, so users don't have obvious control over
> which flash pages are being read. To write to flash, one has to do
> things to ensure that nothing needs to read the flash chip for the
> duration of the write.
> 
> That's a big hassle to save 24 cents of SPI flash chip off to the
> side.

And the price of a circuit board!

> 
> I guess the flash cache approach might trash IRQ latency. The flash is
> 4-lane SPI.  I think we can tell the compiler to put the ISRs and some
> bits of time-critical code into the bigger (256 Kbytes) SRAM.
> 
> Our biggish sine lookup table could be plopped into SRAM too, to
> reduce thrashing.
> 

-- 
“But what a weak barrier is truth when it stands in the way of an 
hypothesis!”

Mary Wollstonecraft

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RP2040 reset idea john larkin <JL@gct.com> - 2024-09-16 19:58 -0700
  Re: RP2040 reset idea Sylvia Else <sylvia@email.invalid> - 2024-09-17 12:16 +0800
    Re: RP2040 reset idea john larkin <JL@gct.com> - 2024-09-17 07:10 -0700
  Re: RP2040 reset idea Arie de Muijnck <noreply@ademu.nl> - 2024-09-17 10:49 +0200
    Re: RP2040 reset idea john larkin <JL@gct.com> - 2024-09-17 07:15 -0700
      Re: RP2040 reset idea Arie de Muijnck <noreply@ademu.nl> - 2024-09-17 17:39 +0200
  Re: RP2040 reset idea The Natural Philosopher <tnp@invalid.invalid> - 2024-09-17 11:07 +0100
    Re: RP2040 reset idea john larkin <JL@gct.com> - 2024-09-17 07:20 -0700
    Re: RP2040 reset idea john larkin <JL@gct.com> - 2024-09-17 09:09 -0700
      Re: RP2040 reset idea The Natural Philosopher <tnp@invalid.invalid> - 2024-09-17 17:21 +0100
        Re: RP2040 reset idea john larkin <jl@650pot.com> - 2024-09-17 15:33 -0700
          Re: RP2040 reset idea john larkin <jl@650pot.com> - 2024-09-18 12:56 -0700
            Re: RP2040 reset idea Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-09-19 02:45 +0000
              Re: RP2040 reset idea John R Walliker <jrwalliker@gmail.com> - 2024-09-19 10:02 +0100
          Re: RP2040 reset idea Lasse Langwadt <llc@fonz.dk> - 2024-09-20 00:09 +0200
            Re: RP2040 reset idea The Natural Philosopher <tnp@invalid.invalid> - 2024-09-20 09:20 +0100
              Re: RP2040 reset idea Theo <theom+news@chiark.greenend.org.uk> - 2024-09-20 11:30 +0100
                Re: RP2040 reset idea john larkin <jl@650pot.com> - 2024-09-20 11:00 -0700
                Re: RP2040 reset idea The Natural Philosopher <tnp@invalid.invalid> - 2024-09-21 09:12 +0100
                Re: RP2040 reset idea john larkin <JL@gct.com> - 2024-09-21 08:08 -0700
                Re: RP2040 reset idea The Natural Philosopher <tnp@invalid.invalid> - 2024-09-21 19:29 +0100
                Re: RP2040 reset idea john larkin <JL@gct.com> - 2024-09-21 12:43 -0700
                Re: RP2040 reset idea Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2024-09-21 19:50 +0000
                Re: RP2040 reset idea john larkin <JL@gct.com> - 2024-09-21 12:56 -0700
                Re: RP2040 reset idea Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2024-09-21 20:46 +0000
                Re: RP2040 reset idea john larkin <JL@gct.com> - 2024-09-21 16:11 -0700
                Re: RP2040 reset idea The Natural Philosopher <tnp@invalid.invalid> - 2024-09-22 09:33 +0100
                Re: RP2040 reset idea john larkin <JL@gct.com> - 2024-09-22 08:28 -0700
                Re: RP2040 reset idea druck <news@druck.org.uk> - 2024-09-23 11:52 +0100
                Re: RP2040 reset idea Bob Martin <bob.martin@excite.com> - 2024-09-24 04:40 +0000
                Re: RP2040 reset idea The Natural Philosopher <tnp@invalid.invalid> - 2024-09-22 09:32 +0100
                Re: RP2040 reset idea john larkin <JL@gct.com> - 2024-09-22 10:46 -0700
                Re: RP2040 reset idea The Natural Philosopher <tnp@invalid.invalid> - 2024-09-22 09:30 +0100
                Re: RP2040 reset idea john larkin <JL@gct.com> - 2024-09-22 10:51 -0700
                Re: RP2040 reset idea dplatt@coop.radagast.org (Dave Platt) - 2024-09-21 20:08 -0700
                Re: RP2040 reset idea The Natural Philosopher <tnp@invalid.invalid> - 2024-09-22 09:37 +0100
  Re: RP2040 reset idea Theo <theom+news@chiark.greenend.org.uk> - 2024-09-17 16:42 +0100
    Re: RP2040 reset idea john larkin <JL@gct.com> - 2024-09-17 19:02 -0700

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