Other Parts Discussed in Thread: AM1806
Hi All,
I would like to ask some questions on timer module.
I notice that there are differences in the reference signal for timer module on different TI chips.
For DM6437, according to page 8 of SPRU989, the timer has source from within the chip and is fixed, which does NOT change with the speed of external oscillator used to drive the DSP.
For C5510, according to page 12 of SPRU595c, the timer uses CPU clock, which is therefore subject to change.
For AM1806, according to page 8 of SPRUFV9a, its Real-Time clock module requires an external crystal with fixed 32,768-KHz frequency, which RTC uses as the base for time and calendar counting.
So are these difference just design choices to suit different needs? For ARM chips, the RTC module even has calendar in addition to normal timing interrupts/(periodical signal) functionality, together with the requirement on 32,758 KHz external clock, should be all designed for ease of programming as a general purpose processor.
For 6437, if the chip has within itself a fixed frequency clock, then the use timing functionalities is also made easy. For example, for a chip whose maximum clock rate is 700MHz, not matter what actual clock rate it is running at (400, 500, 600MHz), code relating to timing doesn’t need to be changed.
And for C5510 whose clock signal changes with CPU clock, then once the CPU clock changes, either due to change in internal PLL or external oscillator, all timing functions needs to be updated to accord with the new clock cycle period. This made programming harder and more prone to clock cycle period counting error.
So this comparison shows that DM6437 and AM1x are has timing module that are easier to use than C5510. Between DM6437 and AM1x, DM6437 is even more stable in the sense that no additional caution needs to be taken on timing crystal. For AM1x, if we supply a wrong crystal oscillator, say 75,536-KHz which is two times of 32,768-KHz, then its timing module runs two times faster than it should, hence will give the wrong timing.
Are these correct?
In this post (Different clock rate, different count?) Brad Griffis suggested that
Brad Griffis said:You mentioned in one of your other posts that xdctools platform wizard specifies the frequency as 594 MHz for DM6437. That's because the OS has its own internal time base and so it needs to know how fast it is being clocked.
But for DM6437, since CPU clock rate doesn’t affect timer clock rate, supplying the wrong clock rate information in the Platform Wizard, say, 594MHz to a DSP running at 700MHz, actually will NOT cause any error in timing functions.
Is this correct?
Sincerely,
Zheng
