USB ERROR CORRECTION?

[pilgrum]

I would like to know how you can have error correction with out a memory buffer and whats the delay involved when using a dac with bi directional talk and error correction? I was wondering because several dac's state they do this but by looking at one or two of the boards i don't see any memory modules that would hold the data and analyse it. I am not an computer or electrical engineer but it struck me as odd. I was under the assumption that in order to compare the data you would need 2 file locations. Is there memory built into the a dac chip itself or the usb controller? Or is this a false statement?

 

[pilgrum]

it's very common for complete designs (computer, program ROM, data RAM, and interface logic) to be inside one chip. often these are FPGAs (field-programmable gate arrays), essentially hardware that can become whatever you want it to be. the designer works as if he's drawing a normal schematic (or uses a logic language like verilog), and the design tool spits out data that goes into a little PROM, which is loaded into the FPGA at power up. Error detection is embedded in the data stream and corrections applied one block at a time.

 

The format of the data stream determines how robust the detection and correction can be.

 

Data file transfers can be guaranteed error free. Media streaming assumes that the transfer will continue even if there are uncorrectable errors. They are filled in fro the before and after parts of the stream.

 

Then there's the business of jitter. A great DAC will have it's own clock and will reconstruct the waveform before converting it to analog.

 

you MUST have a memory buffer to stream anything from USB. it has nothing to do with error correction. USB is bursty (sends small packets at high speed, with pauses in between), and the DAC wants one sample per sample clock tick.