Re: Microcontroller selection

linnix wrote:
On Jun 27, 5:00 pm, Jim Granville <no.s...@xxxxxxxxxxxxxxxxxxxxxx>

Since you are targeting JTAG, I'd suggest a simple Compression wrapper
on the USB link. The JTAG clock data has to be uncompressed, but
you can stream the USB data compressed, and that will remove any USB
bottleneck. - and it is the long datastreams that will benefit the most
from compression.


It's not always so simple. I have an ARM chip with a slow Jtag/debug
wire. Fast USB datastreams would overrun the ARM state machine. I
have to slow down the USB side just to avoid overrunning the ARM
chip.

Of course, I'd expect any half-decent implementation to allow control
of the JTAG clock speed, and to have handshakes so that any JTAG clock speed was supported.
A smarter system might even allow block-setable JTAG speeds, and
even a CPLD to fan-out the JTAG, so that systems might have a FAST and
SLOW jtag branches.

Mostly I was focusing on getting the highest possible streaming speed,
on a std system. Once you have that, it's pretty trivial to slow it down
later :)

-jg

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