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Per Westermark
06/18/10 02:49
Read: 576 times
Sweden


 
#176739 - Huge FIFO because max baudrate also much higher
Responding to: Andy Neil's previous message
Both USB and PCI introduces latencies. These latencies means that bit-banging does not work well. You can't react instantly to control signal change. Extra latencies means that a FIFO is needed.

But the big reason for really huge FIFOs on the USB-connected serial ports is that they not only have a high latency from USB and PCI. They normally also supports baudrates of 1Mbit/s or more - the 16-entry FIFO is much used and appreciated already at 115200 baud. Step up the baudrate a factor 10 and it is also reasonable to have ten times larger FIFO to allow caching for the same number of milliseconds. At 1Mbit/s you get 100k characters/second or 100 characters/ms. 1ms is also the framing speed of the USB protocol so a FIFO must be able to span (at the very least) this time frame.

List of 23 messages in thread
TopicAuthorDate
Serial Port monitor software      David Good      06/15/10 13:42      
   Docklight      Rob Klein      06/15/10 14:00      
      I use...      Michael Karas      06/15/10 20:49      
   monitor and control      Juergen Christoph      06/16/10 02:14      
      br@y terminal??      Jerson Fernandes      06/16/10 02:31      
         But that's "just" (sic?) another terminal, surely?      Andy Neil      06/16/10 03:25      
      RE: Portmon from Sysinternals      Andy Neil      06/16/10 02:35      
         "pi" cable and two serial ports to log rx and tx      Per Westermark      06/16/10 03:23      
            OK for simple data logging...      Andy Neil      06/16/10 03:27      
               timing etc is just a question of program and OS      Per Westermark      06/16/10 03:56      
            Command-response sync?      Oliver Sedlacek      06/16/10 04:41      
               Don't blame windows here!      Andy Neil      06/16/10 05:14      
                  Don't blame the driver or the adapter      Justin Fontes      06/17/10 14:58      
                     Eh?      Andy Neil      06/17/10 16:42      
                        Huge FIFO because max baudrate also much higher      Per Westermark      06/18/10 02:49      
                  USB-Windows-drivers      Oliver Sedlacek      06/18/10 08:01      
                     Digressing: Multiple USB-to-Serial      Andy Neil      06/18/10 08:24      
                        Digressing Further...      Michael Karas      06/19/10 06:57      
                        Nice      Oliver Sedlacek      06/21/10 02:10      
                           RE: It's a shame I can't tell the service guys what to buy      Andy Neil      06/21/10 02:28      
               8052-based analyser      Andy Neil      06/16/10 05:18      
               Timing just depends on OS and where the data is sampled      Per Westermark      06/16/10 05:38      
      Scripting for development and testing      David Good      06/18/10 10:10      

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