Mity CPU Platforms » MityDSP-L138 (ARM9 Based Platforms)

Hi,

Is the HD not ever detected, or does it occasionally not attach?

-Mike

Hi Jun Mo,

For layout recommendations, be very careful with the SATA layout. Below are some guidelines to verify before building the PCB:

• Use controlled impedance
• Avoid vias
  • Completely avoid them if possible
• If vias cannot be avoided
  • Minimize via stubs - go top to bottom layer transition, use a blind via, or back drill
  • At the layer transitions, make sure there is a return current path by adding GND vias near the signal vias to connect the reference planes
• Ensure there is a continuous reference plane (GND) under the SATA tracks with a path to the GND connections on the edge connector
• Maintain sufficient spacing to other copper (even GND, but especially active signals) around the SATA pairs, such as 3X the trace width
• For clean power, keep VCC and GND planes coupled together with as much area as possible
  • Bypass caps have a limit to the high frequency response
  • At high frequencies, the plane capacitance responds
• For cleaner bypass caps, connect vias to side of pads instead of ends (lower parasitic inductance)
• Layout power connections to minimize routed lines - instead go nearly direct to vias to get the power or ground plane with minimal parasitics
• Read up on high speed layout
  • There are lots of resources on the web
  • Could start here: http://www.ti.com/lit/an/scaa082/scaa082.pdf
• Use sufficient bypass caps of large and small values
  • Kemet has a nice Cap spice sim for evaluating options: http://www.kemet.com/Spice

Thank you for your reply.
The HD is occacionally not attached. And the possibility of attahement depend on the brand of SSD. Intel SSD can be connected most of the time, Kingston has lower possibility on connection, and Samsung has very low possibility on connection.
And when I look at the wire on the SOM module, it is hard to say whether the length of the wire in each pair identical from the pin of the chip to the edge of the module. So I do not know whether I need to do any wire length compensation on my own mother board, or I only need to make sure the length of each pair identical from the SODIMM connector to the SATA cable connector on my own board.

I am fairly certain that the lengths on the module for the SATA lines are matched. I will check with our PCB designer.

Do your boards ever negotiate to SATA-I speeds instead of SATA-II speeds? You should be able to see the negotiated speed by checking the kernel log messages with dmesg.

-Mike

From the kernel boot message, occasionally it failed to link to 3G speed, it linked up to 1.5G, but most of the time if link to 3G failed, it failed totally at all. Even though it linked up at 1.5G, it failed to mount the file system.

Jun Mo

What version of the kernel are you using?

The SW developer told me the kernel version is 2.6.34
Does that affect the quality of link?