Arm, gdb and jtag

Alaric B Snell wrote:
> 
> Ralph Malph wrote:
> 
> >>So a dependency upon the Xilinx software :-( Which I bet they don't
> >>provide a version of that will run on a Z80 to dynamically reconfigure
> >>an IO glue FPGA, eh? :-)
> 
> > If you are talking about using different bit streams, then you don't
> > need anything special on the Z80 other than the code to bit bang the
> > configuration data into the part.  If you are talking about *changing*
> > the bit stream in the Z80, then you are working on a very long and
> > tedious project.
> 
> I'd like to be able to generate my own bit stream. I'm not worried about
> the requirements of compiling a logical specification to a description
> of how the PLD should wire itself up, based upon the documentation of
> the PLD's routing capabilities; I can do that, it's just that I can't
> find documentation for how to generate the actual bit stream that will
> make the PLD wire itself up as I wish.
> 
> I've experimented with compiling hardware descriptions for my own design
> of *simulated* PLD :-)

PLDs come in two flavors, simple and complex.  There *are* specs for the
simple PLDs because they consist of only the AND fuse array (AFAIK). 
All 16L8's use the same fuse map, for example.  

The complex CPLDs are all different.  But if you are smart enough to
write your own routing software, you should be clever enough to reverse
engineer the parts from various downloads.  This may be tedious, but it
will work.  The structures in a CPLD are very regular so that you only
need to figure out a part of the device and you then have a much larger
hunk.  

FPGAs are a whole new level of complexity.  But again a lot of the
device is very regular.  But there is a lot more to the irregular part.

Ralph Malph wrote:

> PLDs come in two flavors, simple and complex.  There *are* specs for the
> simple PLDs because they consist of only the AND fuse array (AFAIK). 
> All 16L8's use the same fuse map, for example.  

Aye.

> The complex CPLDs are all different.  But if you are smart enough to
> write your own routing software, you should be clever enough to reverse
> engineer the parts from various downloads.  This may be tedious, but it
> will work. 

You don't have to be very smart to write software to decide how to 
program a PLD unless you're doing what the development tools do and 
accepting arbitrary logic equations. Then you need to allocate logic to 
PALs (or across multiple PALs) within the device based on what 
macrocells need to be connected to what and the capacities of the PALs, 
but then in the PAL generation phase you may find enough common terms 
between equations in a given PAL that it has space left over so other 
bits of logic could be implemented there, saving interconnection matrix 
space... All textbook optimisation techniques, but tricky to develop due 
to a lot of details that need attention.

My application would more be to hand-produce a number of 'macrocell' 
designs, and then at run time decide which 'macrocell' to put into each 
of a number of 'slots', and how to wire them to each other. Which is 
relatively trivial - just compose the bit streams for each macrocell to 
create the fuse maps for the PAL blocks, then work out an interconnect 
fuse map to tie them together.

 > The structures in a CPLD are very regular so that you only
> need to figure out a part of the device and you then have a much larger
> hunk.  

The ones I have lying around consist of four PALs with special I/O 
macrocells (that can be a range of flip flops, mainly) connected with an 
interconnect matrix to each other and the outputs of the chip. I reckon 
the four PAL blocks should be relatively easy to find in the fusemaps, 
particularly since I could probably isolate them by compiling designs 
with varying options for the macrocells to see where the macrocells are 
defined... but it would be much nicer to just get the programming 
documentation for the part :-)

> FPGAs are a whole new level of complexity.  But again a lot of the
> device is very regular.  But there is a lot more to the irregular part.

Yes!

ABS