From 350b7c5939c2e43a29f2986f89b33fd9e11ad0e4 Mon Sep 17 00:00:00 2001 From: Virgil Dupras Date: Sat, 5 Sep 2020 16:52:46 -0400 Subject: [PATCH] avr: improve docs The batch mode thing seems to have been caused by bad timing on my prototype. Now that I've corrected it, live interaction seems to work fine. --- doc/avr.txt | 32 ++++++++++++++------------------ 1 file changed, 14 insertions(+), 18 deletions(-) diff --git a/doc/avr.txt b/doc/avr.txt index 70b3a47..5fd70a0 100644 --- a/doc/avr.txt +++ b/doc/avr.txt @@ -35,26 +35,27 @@ with "(spid)". Then, you initiate programming mode with "asp$", and then issue your commands. -At this time, only fuse commands are implemented. You get/set they values with -"aspfx@/aspfx!", x being one of "l" (low fuse), "h" (high fuse), "e" (extended -fuse). - Each command will verify that it's in sync, that is, that its 3rd exchange echoes the byte that was sent in the 2nd exchange. If it doesn't, the command aborts with "AVR err". -At the time of this writing, it is recommended that you perform your commands in -batch, that is, running your commands right after the "asp$" command, ending -your batch with "(spid)" so that the next batch works. In my tests, interacting -with the chip "live" in a single "asp$" session sometimes resulted in unreliable -data that didn't properly detect sync errors. TODO: investigate further. +# Access fuses + +You get/set they values with "aspfx@/aspfx!", x being one of "l" (low fuse), +"h" (high fuse), "e" (extended fuse). -# Writing data to Flash +# Access flash Writing to AVR's flash is done in batch mode, page by page. To this end, the -chip has a buffer which is writable byte-by-byte. To write to the flash, you -begin by writing to that buffer using aspfb! and then write to a page using -aspfp!. +chip has a buffer which is writable byte-by-byte. + +Writing to the flash begins with a call to asperase, which erases the whole +chip. It seems possible to erase flash page-by-page through parallel +programming, but the SPI protocol doesn't expose it, we have to erase the whole +chip. Then, you write to the buffer using aspfb! and then write to a page using +aspfp!. Example to write 0x1234 to the first byte of the first page: + +asperase 0x1234 0 aspfb! 0 aspfp! Please note that aspfb! deals with *words*, not bytes. If, for example, you want to hook it to A!*, make sure you use AMOVEW instead of AMOVE. You will need to @@ -62,8 +63,3 @@ create a wrapper word around aspfb! that divides dst addr by 2 because AMOVEW use byte-based addresses but aspfb! uses word-based ones. You also have to make sure that A@* points to @ (or another word-based fetcher) instead of its default value of C@. - -Beware of bootloader sections! By default, AVR chips have a bootloader using the -first few pages (by default, the ATMega328P uses 4 pages for its bootloader). -Check (or modify) the BOOTSZ fuses to confirm where you whould start writing -your program.