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   XPost: sci.electronics.design   
      
   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.   
      
      
   --   
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