On the NS7520 you can choose to use a crystal with or without the PLL enabled (this was not possible in NET+50 as I understand it, but is possible on NS7520?). According to the BSP Porting Guide the PLLTST_SELECT defines which clock source to use. The only options are an external clock (SELECT_THE_XTAL1_INPUT) or crystal with PLL (SELECT_THE_CRYSTAL_OSCILLATOR_INPUT). If SELECT_THE_CRYSTAL_OSCILLATOR_INPUT is selected the SYS_CLK is defined by the PLL_CONTROL_REGISTER_N_VALUE. There is no option for crystal without PLL. How do I setup my BSP so that the timing will be correct when I use a crystal but with the PLL disabled?
You CANNOT use crystal without PLL on any of NetArm chips.
If you are correct than “muscleman” (which as i understand it work at netsilicon) doesn’t know what he is talking about. Below you can read a response by muscleman in Jan 2003 regarding the oscillator on NS7520. “7520 is a completely new chip not like the 50 because it allows people to run with external oscillator with or with out pll disabled.” And I hope that you are wrong and “muscleman” is correct but it would be could to get it confirmed.
I know what I am talking about!!! We have lately discovered that we have problems with the pll that it might come up at half clock. Check the latest errata for it’s workaround. Based on this we no longer can say “7520 is a completely new chip not like the 50 because it allows people to run with external oscillator with or with out pll disabled.” Hope this clarifies.
I don’t want to use the PLL so the PLL problem shouldn’t cause any problems for me? I still haven’t got any answer to the real question of this topic. I have analyzed the code (NAgetSysClkFreq and NAgetXtalFreq functions) and it looks like if I select the SELECT_THE_XTAL1_INPUT the timing will be correct but I have to force the PLLTST_SELECT to SELECT_THE_XTAL1_INPUT instead of using the usesTheInternalOscillator() function since this will set it to SELECT_THE_CRYSTAL_OSCILLATOR_INPUT. Will setting the PLLTST_SELECT cause any other problems? It looks like it is only used in the NAgetSysClkFreq and NAgetXtalFreq functions but I am not certain. PS. My intention wasn’t to criticize you (muscleman) just to point out that I had read the hardware reference (and this forum) and I know that you can use a crystal without the PLL otherwise I hadn’t asked the question.
The answer in short NO.