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   PID: SoupGate-Win32 v1.05   
   XPost: sci.electronics.design   
      
   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.   
      
   Will keep me busy through the dark winter days...:-)   
      
      
      
   --   
   There’s a mighty big difference between good, sound reasons and reasons   
   that sound good.   
      
   Burton Hillis (William Vaughn, American columnist)   
      
   --- SoupGate-Win32 v1.05   
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