gnupic: Kernel on PIC
Subject:
Re: Kernel on PIC
From:
"Mark J. Dulcey" ####@####.####
Date:
28 Apr 2002 16:58:50 -0000
Message-Id: <3CCC280A.6070608@buttery.org>
Antonio A Todo Bom wrote:
> With the new generation of PIC18F... will be possible to address up to 2Mb ROM or Dyn-RAM, then I thinking if is possible to port a lite version of Kernel to it.
> Is there anybody thinking about?
> Will be possible to have a quick turn back projects with kernel environment with some libs.
The 18F PICs that are currently available (and I use the term
"available" loosely), the 18F252 and 18F452, do not have an external
address bus. You could create an external memory interface for them
using some of the I/O ports, but it would be a lot slower than using
internal RAM, and you could not execute code from the external memory.
Some of the future products, such as the 18F8720, will have external
program memory addressing capability (up to 2 megabytes). Those are
bigger chips with lots of pins; they will only come in 80-pin TQFP
surface-mount packages. (You lose a bunch of I/O pins when you use the
external memory interface - there are 16 multiplexed address/data lines
and 4 dedicated address lines, plus 7 lines for various control signals
- but on an 80-pin chip, there are still a lot of I/O lines to use.)
There is no DRAM controller on the chip, so it would likely be easier to
use SRAM instead.
Oddly enough, there is no provision for external DATA memory, so you're
stuck with slower programmed methods for doing that, just like on
earlier PICs. It would seem to me that there would be more applications
calling for a couple of megabytes of data than a couple of megabytes of
code, but maybe I just use chips differently than the majority of their
customers do. (Yes, I know about the TBLRD and TBLWT instructions that
let you easily transfer information between program memory and data
memory, but they're still not an ideal solution.)
