mirror of https://github.com/hsoft/collapseos.git
57 lines
2.2 KiB
Plaintext
57 lines
2.2 KiB
Plaintext
# Programming AVR chips
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(In this documentation, you are expected to have an AVR binary
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ready to send. To assemble an AVR binary from source, see
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asm.txt)
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To program AVR chips, you need a device that provides the SPI
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protocol. The device built in the rc2014/sdcard recipe fits the
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bill. Make sure you can override the SPI clock because the sys-
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tem clock will be too fast for most AVR chips, which are usually
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running at 1MHz. Because the SPI clock needs to be a 4th of
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that, a safe frequency for SPI communication would be 250kHz.
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The AVR programmer device is really simple: Wire SPI connections
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to proper AVR pins as described in the MCU's datasheet. Note
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that this device will be the same as the one you'll use for any
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modern SPI-based AVR programmer, with RESET replacing SS.
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The AVR programming code is at B160.
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Before you begin programming the chip, the device must be desel-
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ected. Ensure with "0 (spie)".
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Then, you initiate programming mode with "asp$", and then issue
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your commands.
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Each command will verify that it's in sync, that is, that its
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3rd exchange echoes the byte that was sent in the 2nd exchange.
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If it doesn't, the command aborts with "AVR err".
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# Access fuses
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You get/set they values with "aspfx@/aspfx!", x being one of "l"
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(low fuse), "h" (high fuse), "e" (extended fuse).
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# Access flash
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Writing to AVR's flash is done in batch mode, page by page. To
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this end, the chip has a buffer which is writable byte-by-byte.
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Writing to the flash begins with a call to asperase, which
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erases the whole chip. It seems possible to erase flash page-by-
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page through parallel programming, but the SPI protocol doesn't
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expose it, we have to erase the whole chip. Then, you write to
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the buffer using aspfb! and then write to a page using aspfp!.
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Example to write 0x1234 to the first byte of the first page:
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asperase 0x1234 0 aspfb! 0 aspfp!
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Please note that aspfb! deals with *words*, not bytes. If, for
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example, you want to hook it to A!*, make sure you use AMOVEW
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instead of AMOVE. You will need to create a wrapper word around
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aspfb! that divides dst addr by 2 because AMOVEW use byte-based
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addresses but aspfb! uses word-based ones. You also have to make
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sure that A@* points to @ (or another word-based fetcher)
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instead of its default value of C@.
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