Setting up the Clock System (CS) in TI-RTOS for MSP432

Hi Julian,

You can modify the clock frequencies in PowerMSP432.c but you need to make sure that the core voltage value and flash wait states work with that frequency.  Also, make sure not to overclock the device.  There is no support in PowerMSP432.c for using the external oscillator.  DCO is the only supported clock source. The values in the PowerMSP432 performance levels were worked out by the MSP432 team to handle most cases.  There is a plan in a future release of TI-RTOS to make this more configurable by the user.

The BIOS CPU frequency just tells BIOS what the CPU frequency is actually running at, but does not change the frequency.  This is important since it may be used in setting up the Clock timer period.  For example if the Clock module is using the lm4 timer (as for Tiva devices), the timer period is a function of BIOS.cpuFreq and Clock.tickPeriod.  If BIOS.cpuFreq does not reflect the actual frequency that the CPU is running at, the Clock ticks will occur at the wrong rate.

The ClockFreqs for MSP432 is used in setting the msp432 Timer period.  It can also be used by other TI-RTOS drivers that need the ACLK frequency.

I'm not sure I understand your question 2.  Is this something you are seeing in XGConf?

Best regards,

Janet

Hi Janet,

When you say "There is no support in PowerMSP432.c for using the external oscillator", are you saying "don't do it", or "we haven't done it yet"? We would like to use the external oscillator and TI-RTOS, so can we just start the clock and tell the RTOS what the frequencies are, or doed the power saving code rely on the DCO, and we should avoid the external oscillator?

Regards,

Josh

Hi Janet,

Thanks for your feedback. 

Regarding question 2 - for the timer module, I can click on a link "device-specific timer support" on the Timer module settings:

This takes me to the Timer-Module settings for the MSP432 which I enable.

Once MSP432 timers are enabled I can create an instance, and in the advanced settings I have the option to select the clock source for the Timer (ACLK/SMCLK).

• This setting is NOT available for instances of the HAL Timer module.
• You may need to close and reopen the .cfg file to see the MSP432 specific timer module in the outline pane.

It appears (looking at register configurations) that both the Clock module and the Timer modules use TimerA peripherals in the MSP432.

If I can set the clock source for a Timer module instance (after all, at the hardware level, it is just a register setting), how do I do the same for the clock module?

Cheers

Julian

Cheers

Julian

Hi Josh,

The PowerMSP432.c makes these assumptions (copied comments from source file):

/*
 * Notes for initial implementation of Power_setPerformanceLevel()
 *
 * 1) There are three performance levels supported:
 *
 *    Level    MCLK (MHz)    HSMCLK (MHz)    SMCLK (MHz)    ACLK (Hz)
 *    -----    ----------    ------------    -----------    ---------
 *      0         12              3              3           32768
 *      1         24              6              6           32768
 *      2         48             24             12           32768
 *      3         48             48             24           32768
 *
 *    Only three of the peformance level constraints are supported:
 *
 *        PowerMSP432_DISALLOW_PERFLEVEL_0
 *        PowerMSP432_DISALLOW_PERFLEVEL_1
 *        PowerMSP432_DISALLOW_PERFLEVEL_2
 *        PowerMSP432_DISALLOW_PERFLEVEL_3
 *
 * 2) DCO is the only supported clock source (all clocks are derived from this;
 *    LF and HF XTALs are not used)
 *
 * 3) ACLK is fixed (and not included in the PowerMSP432_PerfLevel structure)
 *
 * 4) DCDC is assumed to be available
 *
 * 5) Hardware interrupts are disabled during the change of performance level
 *
 */

So if you use the external oscillator instead of DCO, you would need to modify the PowerMSP432 code.

Best regards,

Janet

Hi Julian,

I think the Clock module is only displaying properties of the ITimer interface, which is why you don't see the device specific Timer settings.  You can work around your problem of setting the input source for the Clock Timer by creating your own timer and setting the Clock.tickSource = Clock.TickSource_USER ("Application code calls Clock_tick" in XGConf).  The Clock module cdoc has an example of .cfg code to do this:

 *  // Tell the Clock module that YOU are providing the periodic interrupt
 *  Clock.tickSource = Clock.TickSource_USER;
 *
 *  // this example uses the ti.sysbios.timers.dmtimer.Timer module
 *  var Timer = xdc.useModule('ti.sysbios.timers.dmtimer.Timer');
 *
 *  // Change Timer 3 frequency to 24 Mhz from default if necessary
 *  Timer.intFreqs[3] = { hi:0, lo:24000000 };
 *
 *  // create a dmtimer config parameter object
 *  var timerParams = new Timer.Params();
 *
 *  // make sure you set the period to 1000 us (1ms)
 *  timerParams.period = 1000;
 *
 *  // custom dmtimer config parameters here...
 *  timerParams.twer.ovf_wup_ena = 1;
 *
 *  // Create the timer.
 *  // This example uses timer id 3.
 *  // Provide your own timer interrupt handler function.
 *  Timer.create(3, '&myTimerTick', timerParams);
 *  @p
 *
 *  In your 'C' code, add your timer interrupt handler and have it
 *  call Clock_tick(), which will perform all of the Clock module
 *  tick duties:
 *
 *  @p(code)
 *  #include <ti/sysbios/knl/Clock.h>
 *
 *  Void myTimerTick(UArg arg)
 *  {
 *       Clock_tick();
 *       ...
 *  }

Best regards,

Janet

G'Day Janet,

Thank you for answering this question for me! This seems like a heavy solution given that the underlying hardware can solve the problem with just a register change (as we know from the Timer module), but it works and I'm happy to go ahead with it.

Unfortunately, I've realized that this was another question that was bubbling in my mind, but was not related to my original question in this thread.

Going back to your question about what I meant by point 2 in my original post.

I guess I wasn't really asking 4 different questions - just listing 4 places where "clock frequency" related settings can be made and asking what the relationship between them is.

For the second item in my list, if you create an instance of the Timer (ti.sysbios.hal) module, in the advanced settings, you can set an "External input clock frequency".

So, to ask my original question a bit differently... It seems that PowerMSP432.c is the "root" for all clock settings. If I want a clock frequency (whether its MCLK, SMCLK, HSMCLK or ACLK) that is not available, is it enough to JUST change that file and recompile or do I need to go into the GUI and change some of the items in my list?

Cheers
Julian

G'Day Janet,

> If you use SMCLK for the Clock timer, and the frequencies of SMCLK in

> PowerMSP432 change for the different performance levels, the Clock

> ticks will be off.

Does this remain true if I use the  Clock.tickSource = Clock.TickSource_USER method to change the Clock tick source?

Returning to a couple of earlier comments took from PowerMSP432.c

* 2) DCO is the only supported clock source (all clocks are derived from this;

*    LF and HF XTALs are not used)

Can be problematic where accurate timing is required.  E.g. if you want to sample at accurate intervals, or if you want to provide an accurate clock for the RTC.  But I think we can get around this in our application.  

* 4) DCDC is assumed to be available

This might be a more serious problem for us.  We found (at least in RevB silicon) that the DCDC introduces a lot of noise to ADC measurements.  Is there any way to force use of the LDO?

Finally, in my TI-RTOS install (v2.20.0.06 - seems to be the latest version) I only have 3 performance levels, while the snippet from PowerMSP432.c you included above has 4 levels (I don't have the SMCLK = 24MHz mode).  That is fine - you probably have a newer version.  In my install, the highest performance level uses a flash wait state setting of 2, but my understanding is that RevC silicon works with a flash wait state setting of 1.  I guess it has been left at 2 for compatibility, but it leaves a little performance on the table.    Do you see any harm in changing the flash wait state setting? 

Thank you for all your feedback over the last few days.  It's been invaluable.

Julian