kbscan: Hardware mode?

[crawfxrd]

As a follow up to #362: can most of the kbscan logic be done by hardware?

• Configure matrix scan via SDC1R, SDC2R, SDC3R
  • Set matrix dimensions via SDC2R@KSOPCS
  • What does "The following timing is based on clk_ec = 8MHz" imply for the values?
  • What do the other fields really do?
    • "Scan Loop Select"?
    • "Wait KSO High/Low Delay"?
    • "Spacing Delay Between Rounds"?
• Enable scan data via SDC1R@SDEN
• Check SDSR@SDV to see if matrix data is valid
• Read matrix state from KSOnLSDR
• Write-clear SDSR@SDV

There is also an interrupt for Scan Data Valid (INT84) that can be enabled (in addition to the one for KSI (INT11) that is for waking the system).

[crawfxrd]

It works, but doesn't really improve anything over the software-based solution.