Hanns-Konrad Unger <[EMAIL PROTECTED]> wrote: > How about a standard USB-RS-232 converter with application AVR910? > Pros: very cheap, no smd > Cons: ??? (what are the known problems of AVR910?)
It will be dog slow, as the AVR910 protocol is a one-byte-at-a-time protocol. USB however is a packet-oriented protocol, so each single byte has to travel across the bus as a separate packet. Also, as the converter stands no chance of knowing whether any further data will follow, it imposes a timeout before assembling a packet and transmitting it, further delaying the processing. Our computer grandfathers already knew that request-response protocols are seriously flawed from a performance point of view, so even protocols like UUCP or Kermit use some kind of "window" where each side can send unacknowledged data in advance. (TCP then improved this method again by introducing a window that adapts itself to the latency and packet error rate of the transmission line.) More intelligent programming protocols like the STK500 one don't suffer that much from being packeted into USB as they send larger blocks of data for anything that has a larger performance impact. (Still, reducing the device's timeout improves the transfer speed, at the cost of cranking up the interrupt rate to be processed by the host, even while the chip is idle.) What's your grief with soldering SMD? It's not all that hard, at least not with the pitch used for the devices in question (0.8 mm). It starts to get messy with 0.5 mm pitch, or with BGAs. -- cheers, J"org .-.-. --... ...-- -.. . DL8DTL http://www.sax.de/~joerg/ NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-) _______________________________________________ AVR-chat mailing list [email protected] http://lists.nongnu.org/mailman/listinfo/avr-chat
