Today I stumbled across a piece of information that surprised me. Apparently there is a minimum cable length for SATA. From Seagate, a reputable manufacturer of SATA devices:
Serial ATA (SATA) data cable lengths
Serial ATA cables are available in many lengths up to 1 meter. Minimum cable length is 12 inches, using shorter cables can cause timing, or noise interference on the cable.
That is all the information they offer, and I could not find much information elsewhere. It is obvious that a cable can be too long: Signals will arrive too late, and eventually become attenuated. This is the first time I hear about cables being too short.
Since they measure the minimum length in inches it makes me think that it is not in the official standard, and something that they have found by trial-and-error, but can someone explain why this would be a problem in a (presumably well designed) standardized high frequency serial protocol?
Best Answer
I have designed SATA asic serdes circuits and do not recall issues with short cables.
However, we do test for very long and very short length test cases to ensure sufficient signal integrity at either extreme, as sometimes a timing circuit or equalizer misbehaves when the signal is too clean.
For instance the timing recovery relies on a sloped transition between 0 and 1, and if the cable is too short, then the 0-to-1 and 1-to-0 slopes are too steep, and the timing recovery can become noisy (it's a long story). This can be an issue in asic test set-ups, but hardly in real deployments.
However, 12in seems to be a ridiculously high minimum.