ARM Technical Support Knowledge Articles

How do I change clocks on the Versatile Express Motherboard V2M-P1?

Applies to: V2M-P1

Scenario

The Versatile Express Motherboard has got six programmable oscillators on board. The output values for these oscillators have been selected to provide the highest performance whilst keeping system stability, however users often want to change the default clock settings for benchmarking, test purposes, etc.

An inappropriate procedure to change the clock settings can lead to system lock-up problems and as a consequence the need of issuing a hardware reset for system recovery.

In this Knowledge Article we discuss some alternative methods that can be used to change the clock settings safely.

Answer

Changing clocks from Reset

ARM recommends to change the clocks on the Motherboard Express V2M-P1 by editing the "board.txt" file, that is located in the USBMSD at the following default path \MB\HBI0190D, before reset. For more information on the Motherboard Express clocks and the safe frequency range for each clock, please refer to the Motherboard Express V2M-P1 Technical Reference Manual available from the Versatile Express DVD or the ARM Website at

infocenter.arm.com/help/index.jsp

The "[OSCCLK]" section in the "board.txt" file can be edited to modify the oscillators' output values on the Motherboard and set the clocks for the following devices:

Alternatively, the oscillators' output values can also be changed at run time by one of the following methods.

Changing clocks at run time

-Method 1: using the Boot Monitor "Configure" submenu:

Enter the Configure submenu by typing "Configure" on the Boot Monitor command line. Type "Help" to obtain the list of commands available from this submenu.

Following an example on how to view the oscillators' output values after reset and how to switch to a different frequency 

Configure> HELP DISPLAY CLOCK


DISPLAY CLOCK [MB|DB1|DB2] [POSITION <number>] OSC <device>

Note: If the first option [MB:DB1:DB2] is not specified on the command line above, the Boot Monitor will interpret "MB" by default for the motherboard oscillators.

-Method 2: Using the Debug submenu of the MCC command line (CFG command)

The Debug submenu of the MCC is only available in running mode from:

                      MBLOG: TRUE                     ;LOG MB MICRO TO UART1 in run mode

For example, to change the output value for OSC 0 on the Motherboard Express:

Cmd> DEBUG

Debug>CFG W OSC MB 0 0 40

MB OSC0 clock set = 40.000Mhz

For a detailed description of the MCC command line interface on how to use different submenus and options, please refer to the Motherboard Express TRM.

Clock Frequency =  40.000 MHz
Displays requested clock in Hz.


Configure> DISPLAY CLOCK MB OSC 0
Clock 0 Frequency =  50.000 MHz

Configure> HELP SET CLOCK
SET CLOCK [MB|DB1|DB2] [POSITION <number>] [DCC <number>] OSC <device> FREQUENCY <value>

Sets requested clock in MHz.
Configure> SET CLOCK MB 0 OSC 0 FREQUENCY 40

Configure> DISPLAY CLOCK MB OSC 0

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