Tony wrote:
The software may be 'free',
I specifically didn't use that word because it definitely is not
"Free Software".
Agreed.
but the machine to run it on, and the OS to
run it under, most certainly aren't.
I didn't pay any money for the Linux OS I run it on. And it will
I didn't realise there was a linux version out now. I've only ever seen
Windows versions...
run (perhaps slowly) on cast-off Pentium machines that
people simply
throw away.
For the <nth> time, I have never been offered a Pentium machine. In fact
I've never been offered a PC more powerful than a 286. On the other hand,
all 4 of my PERQs, most of my PDP11s, most of my HP desktops, etc were
free...
When DECUS gives you a "free" C compiler for the PDP-11, do you
complain about having to pay for the PDP-11 computer and the
RT11 operating system?
No, but there's a big different. The only real use for a PDP11 C compiler
is to program PDP11s. If you don't have a PDP11, you probably don't want
a C compiler for it. This is not the case for FPGA development tools (you
could want to program an FPGA without owning any specific type of computer).
And another difference was that if I want to program in C, I have a large
choice of possible machines. I could use DECUS C on a PDP11. I could use
GCC on just about anything. I could even try writing my own compiler (the
C standard is available, albeit most certainly not free, the programming
specs for many computers are available). But if I want to use these
FPGAs, I have to use the manufacturer's software on their choice of
computers.
And I do have an objection to
trusting my design to a piece of binary-only software that I have no easy
way of checking if it's doing the right thing
The Xilinx FPGA Editor lets you see *exactly* how the resulting logic
is wired in the device. However, unfortunately the FPGA Editor is not
included in the no-charge dowloadable software; it's only in the paid
version, which costs US$500 and up.
Having done battle with older Xilinx chips (and hated every minute of it!
[1]), I found the editor to be absolutely essential to undo the damage
done by the rest of the software. If that's not included, then IMHO the
package is worthless for serious work.
[1] This was about 10 years ago, on a high-spec PC for the time. A
compilation cycle took _overnight_. Which meant that if I made a small
change to the design I couldn't test if until the next morning. I could
have hand-wired the darn design quicker.
(it's very difficult to be
sure a CPLD or FPGA is doing the right thing under _all_ conditions).
It's difficult to tell whether any collection of thousands, tens of
thousands, or hundreds of thousands of gates are doing the right thing
under all conditions, regardless of whether they're in an FPGA, or a
bunch of 7400 NAND gates you've wire-wrapped. In fact, it's
essentially impossible.
But it's a darn sight easier if you can probe 'internal' signals...
I would mind if they'd properly document the
chips so I could write my
one CAD software if I wanted to. But they don't. AFAIK there is no 100%
documented CPLD or FPGA available (100% documented meaning you can go
from design to chip without proprietary software or a proprietary
programmer).
There are plenty of completely documented CPLDs, and no completely
documented FPGAs.
You're saying there's a CPLD that I can program without using a single
piece of proprietary software or a proprietary programmmer (In other
words, I can start from my schematic/logic equations, turn it into the
programming data, by hand if need be, and then get that into the chip
without having to use anything undocuemtned)? Can you please tell me some
familes/companies?
Xilinx did completely document one FPGA family (XC5200? XC6200? I've
forgotten). It didn't sell well, so they discontinued it.
XC6200 (there were going to be at least 2 chips the XC6216 and the
XC6264). I got the data sheets and connected the UK distributors. By the
time they thought they could get me some 'sample quantity' chips, the
darn things had been discontinued. That's why I never used them/
However, I don't *really* think you want to spend
the rest of your
life writing your own FPGA development software. It's a hard problem
and there are hundreds of thousands of man-years of development effort
Sure. I am not saying I want to write the tools myself, but if the specs
were available, I am sure some clever programmers would start writing
open-sourcce versions (as has happened with so many other things!).
-tony