HP Prime too complicated

[cyrille de brébisson]

Hello,

About USB and serial.
As far as I Can tell, serial is going away as an external data path.
Serial is still used INSIDE systems, to comunicate (like SPI and I²C), but it has been a very long time since I have seen anything with an external serial com (exception for old systems of course)...

USB-Serial convertors are usually crap. Not only do they nearly all require specific drivers, but in addition, they never work well. And the reason is that USB is a milisecond, packet based system while serial is a 1/10th of a ms byte based system.

As a result, on top of serial, most systems will implement some type of packet based system (xModem for example), and this system will require ack bytes to be sent back within some time frame.

Put it all together and you get this:
On the PC, the "sender" sends a bunch of bits doing FileWrite calls.
The converter driver will wait until it has a full packet, or for a given amount of time if not and send the bytes (note the first delay there).
The receiver will reply and send bytes back to the converter.
It, itself will wait for a full packet or a delay before sending a full USB packet.
All these delays cause, at best the serial protocols that are riding on top of the converter to slow down, or even to stop working due to timeouts (depends on the protocol and how good/bad the serial converter an it's drivers are)...

I actually had to change the timeouts in the latest versions of the 49 xmodem code (at the time) to try to mitigate the problem with the USB convertors that were comming up at the time.



I like HW tinkering and, yes, it woudl be great to be able to do this on something like Prime...
However, HW tinkering can easely lead to HW failures, and then guess who would see the units comming back under waranty :-( So, if anything ever got done, it would most likey be done through a separate HW board that connects to Prime through USB or the like. With issues similar to the one that I just described.

Cyrille