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   PID: SoupGate-Win32 v1.05   
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   XPost: sci.electronics.design   
      
   On Sat, 21 Sep 2024 19:29:26 +0100, The Natural Philosopher   
    wrote:   
      
   >On 21/09/2024 16:08, john larkin wrote:   
   >> On Sat, 21 Sep 2024 09:12:06 +0100, The Natural Philosopher   
   >>  wrote:   
   >>   
   >>> On 20/09/2024 19:00, john larkin wrote:   
   >>>> On 20 Sep 2024 11:30:13 +0100 (BST), Theo   
   >>>>  wrote:   
   >>>>   
   >>>>> In comp.sys.raspberry-pi The Natural Philosopher    
   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.   
      
   --- SoupGate-Win32 v1.05   
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