> BTW, notice that there is no "serial port" USB Class. Manufactures
> that produce USB serial port adapters need to supply the drivers,
> which might or might not come preinstalled in an operating system.
The manufacturer's hardware "Serial Converter" drivers are rarely
preinstalled in an operating system.
There is another issue that can cause jitter for EXTFSK and bit bang CW
on USB ports. When more than one USB device is connected to a USB Root
Hub (the motherboard device that normally supports four USB jacks),
each device/connector generally receives data in 8 ms "bursts" if there
is date to/from more than one device.
W5XD has recognized this issue in Writelog and includes information
on configuring the USB serial devices for faster response (smaller time
slots). microHAM Router also includes the ability to set "USB Response
time" but there are limitations on what can be accomplished when an
external hub is used. Note, many commercial interfaces package a
USB hub with five or six USB to serial converters and the USB Audio
Class device.
73,
... Joe Subich, W4TV
microHAM America, LLC.
http://www.microHAM-USA.com
http://groups.yahoo.com/group/microHAM
On 6/18/2010 5:56 PM, Kok Chen wrote:
>
> On Jun 18, 2010, at 2:08 PM, Richard Ferch wrote:
>
>> However, according to the documentation for JE3HHT's implementation
>> of EXTFSK (comfsk105.zip), it uses the multimedia timer to control
>> timing.
>
> The Windows multimedia timer is specified with a granularity of 1 ms
> (http://msdn.microsoft.com/en-us/library/dd757633(v=VS.85).aspx).
>
> Isochronous transfers is something different. See for example here:
>
> http://www.silabs.com/Support%20Documents/TechnicalDocs/AN295.pdf
>
> Notice that USB isochronous transfers are only available for the USB
> Audio Class, not even for mass storage class (which don't care if you
> inject pauses now and then), for example.
>
> You can find information about other USB class here
>
> http://www.usb.org/developers/devclass_docs#approved
>
> BTW, notice that there is no "serial port" USB Class. Manufactures
> that produce USB serial port adapters need to supply the drivers,
> which might or might not come preinstalled in an operating system.
>
> 73 Chen, W7AY
>
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