INTL 3:770/1 3:770/3
REPLYADDR tnp@invalid.invalid
REPLYTO 3:770/3.0 UUCP
MSGID: f158f9b4
REPLY: 7baa214b
PID: SoupGate-Win32 v1.05
XPost: sci.electronics.design
On 22/09/2024 00:11, john larkin wrote:
> On Sat, 21 Sep 2024 20:46:52 -0000 (UTC), Phil Hobbs
> wrote:
>
>> john larkin wrote:
>>> On Sat, 21 Sep 2024 19:50:34 -0000 (UTC), Phil Hobbs
>>> wrote:
>>>
>>>> john larkin wrote:
>>>>> 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.
>>>>>
>>>>>
>>>>
>>>> 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
--- SoupGate-Win32 v1.05
* Origin: Agency HUB, Dunedin - New Zealand | Fido<>Usenet Gateway (3:770/3)
SEEN-BY: 10/0 1 90/1 103/705 105/81 106/201 124/5016 129/305 153/757
SEEN-BY: 153/7715 218/0 1 601 700 840 870 930 220/70 221/1 6 360 226/17
SEEN-BY: 226/30 100 227/114 229/110 111 114 200 206 300 317 400 426
SEEN-BY: 229/428 470 550 616 664 700 240/1120 266/512 267/800 282/1038
SEEN-BY: 291/111 292/854 301/1 113 812 310/31 320/219 322/757 335/364
SEEN-BY: 341/66 342/200 396/45 460/58 633/280 712/848 770/1 3 100
SEEN-BY: 770/330 340 772/210 220 230 5020/400 1042 5058/104 5075/35
PATH: 770/3 1 218/840 221/6 301/1 218/700 229/426
|
