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Tue Oct 2 03:46:01 CEST 2007

dsPIC

maybe it's time to try it out, and gently grow it into being. some
challenges:

- 3 bytes / instruction
- 16 bit datapath
- addressing modes

flash block erase size is 96 bytes, but address-wize this counts as 32
instruction words.

  The dsPIC30F Flash program memory is organized into rows and
  panels. Each row consists of 32 instructions, or 96 bytes. Each
  panel consists of 128 rows, or 4K x 24 instructions. RTSP allows the
  user to erase one row (32 instructions) at a time and to program
  four instructions at one time. RTSP may be used to program multiple
  program memory panels, but the table pointer must be changed at each
  panel boundary.

I don't understand why it says 'four instructions at a time' and then
later on talks about 32 at a time: "The instruction words loaded must
always be from a group of 32 boundary."

And the confusion goes on "32 TBLWTL and four TBLWTH instructions are
required to load the 32 instructions."

this looks like a typo.. let's download a new version of the
sheet. got DS70138C now. they're at version E. it's got the same typo.

so assume i need to write per 32 instructions + some magic every
4K instructions (updating a page pointer?). apart from the latter it's
quite similar to the 18f, just a larger row size size.

it looks like this thing is byte addressed, but for each 2 bytes,
there's an extra 'hidden' byte! lol

ok, there is a sane way of looking at it: the architecture is 16-bit
word addressed, but every odd word is only half implemented:
instruction width is 3 bytes.

it looks like it's best to steer the forth away from all the special
purpose DSP tricks like X/Y memory and weird addressing modes. looks
like an interesting target for some functional dataflow dsl though.

there are 2 kinds of instructions: PIC-like instructions that operate
on WREG0 and some memory location, and DSP-like instructions that use
the 16 registers.

roadmap:
- find a 8bit -> 16bit migration guide from microchip
- partially implement the assembler to PIC18 functionality




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