How do I use the LWB5+ DVK with an SDR104 capable external slot?

Sterling-LWB5+

Answer

The LWB5+ is an embedded SDIO module and using an external slot may introduce some challenges. The external slot likely starts at 3.3 VIO and steps down to 1.8 VIO. If this is not the case, the following also addresses fixed VIO for both 1v8 and 3v3. As noted below, the M.2 variant only supports 1.8 VIO.

  1. Run the LWB5+ at 3.3 VIO SD High Speed mode (module only, not M.2)
    1. Configure the LWB5+ DVK for 3.3 VIO via strapping switches (1,0) and VDDIO switched to 3v3
    2. Add no-1-8-v to the SDIO device node in the device tree
    3. Confirm the voltage step-down is disabled on the host
  2. Run the LWB5+ at SDR speed by syncing VIO via jumper wire (module only, not M.2)
    1. If the host board exposes VIO of the external slot, depopulate the VDDIO switch on the LWB5+ DVK and wire the center pin directly to VIO on the host.
      1. An example is TP709 on the i.MX6UL EVK from NXP
    2. The external slot may not be fully capable of SDR104 @200MHz and the bus speed may have to be limited
      1. Example 100MHz device tree property: max-frequency = <100000000>;
  3. Force the host to run at 1.8 VIO all the time (module and M.2)
    1. This requires modification to the host and is up to you to weigh the risk and devise a resolution
    2. The LWB5+ M.2 DVK will not need modification
    3. Configure the LWB5+ module DVK for 1.8 VIO via strapping switches (1,1) and VDDIO switched to 1v8
    4. The slot may not be capable of full 200MHz SDR104 operation, see note above about limiting bus speed