All,
Currently we are investigating whether we can use a Rabbit RCM3200 uC to read in data on 4 serial ports (at 115200) and to write it to an UDP port. The Rabbit only has a 1 byte 'FIFO', so it is most likely we need an external UART. A complicating factor is that we need to timestamp (1 byte) every single byte that is received.
What type/brand of UART do you guys advice and is it possible to write this timestamp byte into the FIFO directly?
Any suggestion is most welcome.
Ko.
One possibility is to use a UART and a FIFO combined implemented in an FPGA. The FIFO would be wide enough to store the character and a timestamp. The width of the timestamp counter would depend on the resolution needed.
At 115200 bps, characters could arrive every 86.8 microseconds or so per UART. Multiply this by 4 receive streams and you get 21.7us. This would be tough to do on a sustained basis, depending on the processor and structure of your program.
regards, Darcy Roberts
kotido wrote:
To timestamp correctly you need _NO_ HW fifo on RX, and a fast SW routine that grabs the RXchar, and TimeByte, and puts BOTH into a SW FIFO. Once the info is in the (4) FIFOs, unloading it becomes an average data rate/packet size problem, and the hard real time has been taken care of.
-jg
I have written a timestamped serial acquisition routine (only 2 serial ports was needed, though) and I can safely tell you that off the shelf UARTs can't do the timestamping -- it's the ISR that can attach a timestamp to the data received. I'm not sure what 1 byte can do for you, I was attaching a 16 bit tick (from the 8054) and a 24 bit time from the BIOS timer.
I can think of two HW solutions: a) custom UART made out of an FPGA that does time stamping b) a regular UART with a dedicated uC that can read and timestamp data very quickly and reliably, then pass them to the host PC
though my favorite is c) a DOS PC with my own proggy ;-)
Hi, simplest way is I think: 4 ring buffers, ones will are filled by hardware interrupt only received byte+timestamp; process(to UDP or else) its in main loop by difference poiters for "for input" & "for processing'.
Cheers
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