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-IMPORTANT NOTE - read before defining CONFIG_SYS_USE_OSCCLK in your board
- config file!!!
-
-
-WARNING: Wrong settings of this parameter have the potential to
-damage hardware by running the MBX's CPU at frequencies that exceed
-it's rating and/or overdriving the it's SPLL!
-
-
-Ramblings:
-1) Motorola offered 12 different variants of the MBX, 6 823s and 6 860s.
-2) Of these 12 variants, only 2 were entry level boards.
-3) I believe that the 2 entry level boards were the only ones that
- used OSCM clocking. I can't be completely certain of this at this
- point.
-4) Motorola never offered an MBX that ran faster than 50Mhz.
-5) The 10, non-entry level boards, ran at 40Mhz.
-6) The EXTCLK input has a minimum clock of 15Mhz for the 823/860.
-7) Motorola no longer sells MBXs.
-
-Based on this information, I can surmise that the default power-on
-reset clocking was one of the following three options.
-
-Multiplier SPLL Options
-------------------------------------
-513 OSCM is SPLL input
-5 OSCM is SPLL input
-1 EXTCLK is SPLL input
-
-The forth option:
-
-5 EXTCLK is SPLL input
-
-is not possible on MBXs. This is because the minimum EXTCLK input
-frequency is 15Mhz. 5 * 15Mhz = 75 Mhz. There was no variant that ran
-above 50 Mhz.
-
-The board I have borrowed definitely uses a multiplier of 1 for
-EXTCLK and runs at 40Mhz. I even went so far as to put a scope on it.
-
-One of the two default OSCM modes are most likely what was used on
-the entry level boards to cheapen them by eliminating the external
-crystal oscillator.
-
-To add insult to injury, the stupid 860 PLPRCR register retains it's
-multiplication factor through hard resets. You can't clear it out
-because it is battery backed and once it is set wrong, it stays
-wrong. The only way to reset it, so that it takes on it's default
-multiplier is to disconnect all power including external, batteries,
-as well discharging caps on the board. This precludes the fact that
-your 860 may be quite DEAD by this time!
-
-If you don't setup the multiplication factor for boards that use the
-OSCM input, they won't run correctly, but at least they won't be
-dead.
-
-Addtionally, there is no good way to determine the clock input source
-from CPU register data. The only way to deal with this is either hard
-code it, determine the correct value with some rather NASTY timing
-loops, or try to grok it from external data sources. Motorola
-firmware opts for the NASTY timing loops, but needs to configure the
-serial ports to do so.
-
-
-You may have a legitimate need to define CONFIG_SYS_USE_OSCCLK if your
-MBX8xx board is using the OSCM clocking mode.
-
-You better know what you are doing here.