Re: New ARM Cortex Microcontroller Product Family from STMicroelectronics

"Jim Granville" wrote...
One clarify : How credible is your ST contact ? - as I cannot see "share
the same packet buffer" anywhere in the user manual, or drawings, and
nothing suggests that conflict.
Search cannot find 'USB' inside the CAN chapter, nor 'CAN' inside the
USB chapter ?
It also does not make chip-design sense, surely it is harder to
lock/overlap some block resource like that, in this cut/paste world ?

That said, it is a strange thing to 'make up'/ admit to if untrue, so
perhaps it is coming via the errata pipeline ?

-jg

My contacts are very credible. And, unfortunately, what we are discussing is something
that would not be made obvious in data*** diagrams. Data*** diagrams are mean to
provide an overview of functionality in as clear a visual format as possible. Like the
model of the atom, it almost never reflects 100% what's inside the chip.

Chip buffers are RAM, and RAM is very greedy when it comes to die area. Allowing for an
extra buffer could price out the chip as non-competitive, or it could be unwieldy from a
layout POV.

My GUESS - the chip was designed for a primary customer, who wanted either USB or CAN
(but not both). During chip design, a smart marketing person asked about adding the
extra peripheral. Adding the CAN or USB adds small pieces of a penny to the chip cost.
But adding an extra buffer probably priced the chip beyond what was quoted to the target
customer.

Jim, if you want to take this off-line, I can be reached at the first email address on
this page:
http://www.microcontroller.com/Embedded.asp?did=23

-Bill.





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