Choose between Raspberry Pi 4B 4GB and ROCKPro64

[Bernd Walter]

On Wed, Nov 13, 2019 at 02:37:29PM -0700, Ian Lepore wrote:
> On Wed, 2019-11-13 at 22:31 +0100, Bernd Walter wrote:
> > On Wed, Nov 13, 2019 at 01:42:13PM -0700, Ian Lepore wrote:
> > > On Wed, 2019-11-13 at 17:48 +0100, Bernd Walter wrote:
> > > > I just remembered that I own an FTDI FT4232H module.
> > > > This one is capable of 12Mbps with 2k Buffers and high speed USB.
> > > > I have it at a different location - guess I will have to drive
> > > > and
> > > > pick it up.
> > > 
> > > You'll certainly have no trouble with the ftdi 4232.  I've tested
> > > those
> > > at 6mpbs in both directions concurrently without any data loss.
> > > 
> > > IMO, breaking free of the 115200 barrier is long overdue, but it
> > > would
> > > have been nice if the step up everyone took was to 921600, because
> > > virtually all usb-serial support that.  With line-level rather than
> > > ttl-level adapters, 1mpbs is often the effective speed limit
> > > because of
> > > the cheap rs232 line-level chips they use.
> > 
> > I don't think many USB uarts are capable to divide 48MHz into 921600
> > *
> > oversampling without being off too much.
> > The high speed ones are a different beast, since they likely have a
> > PLL and run with an internal 480MHz clock.
> > 
> 
> I don't think I've ever heard of a usb-serial chip that can't do
> 921600, it's a "standard" speed (115200 * 4).  The newer ftdi chips
> still use an external 12mhz clock/crystal, but now they have an
> internal pll that kicks it up to 60mhz, then the baudrate generator
> divides that down.

Ah right - I just thought about 48MHz USB, but of course that already
requires a PLL.

-- 
B.Walter <bernd at bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.