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diff --git a/upgrade/technical details.txt b/upgrade/technical details.txt deleted file mode 100644 index 45fa7ee..0000000 --- a/upgrade/technical details.txt +++ /dev/null @@ -1,51 +0,0 @@ -Technical Details -================= - -A summary of how 'upgrade' works - - --- build process: - -1) Manually run the generate-data.rb ruby script with the new bootloader's hex file: - ruby generate-data.rb new_firmware.hex - If you have trouble running it, make sure you're using ruby version 1.9. 1.8 is too old! - - generate-data.rb creates the bootloader_data.c file, which defines some variables containing - the entire raw byte data of the bootloader as an array stored in flash memory. It also - calculates and writes in the start address of the bootloader. The hex file supplied can be any - bootloader which works similarly to USBaspLoader-tiny85 - which is most (all?) tiny85 bootloaders - and likely some for other avr chips which lack hardware bootloader stuff. - -2) Generate the hex file using make: - make clean; make - - The upgrader hex file is built in the usual way, then combined with upgrade-prefix.hex (which - I wrote by hand) to prefix a fake interrupt vector table in the start of the upgrader. This is - necessary because bootloaders like micronucleus and Fast Tiny & Mega Bootloader only work with - firmwares which begin with an interrupt vector table, because of the way they mangle the table - to forward some interrupts to themselves. - -3) Upload the resulting upgrade.hex file to a chip you have some means of recovering. If all works - correctly, consider now uploading it to other chips which maybe more difficult to recover but are - otherwise identical. - - --- how it works: - -Taking inspiration from computer viruses, when upgrade runs it goes through this process: - -1) Brick the chip: - The first thing upgrade does is erase the ISR vector table. Erasing it sets the first page to - 0xFF bytes - creating a NOP sled. If the chip looses power or otherwise resets, it wont enter - the bootloader, sliding in to the upgrader restarting the process. - -2) erase and write bootloader: - The flash pages for the new bootloader are erased and rewritten from start to finish. - -3) install the trampoline: - The fake ISR table which was erased in step one is now written to - a trampoline is added, simply - forwarding any requests to the new bootloader's interrupt vector table. At this point the viral - upgrader has completed it's life cycle and has disabled itself. It should never run again, booting - directly in to the bootloader instead. - - |