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AM4378: PRU-ICSS spread spectrum clocking

Kris Ganev
Intellectual 385 points

Part Number: AM4378

Hello,

We will be driving a graphic LED display with PRU core on AM4378 Sitara processor. We are currently using BeagleBone Black board for development. I reviewed the Technical Reference Manuals (TRM) of the AM335x and AM437x processors but couldn't find which exact clock drives the PRU processor cores. It sound like it may be the PRU-ICSS_OCP_CLK but it is not explicitly stated.

We need to use the spread spectrum clocking feature of the Sitara DLLs in order to reduce the EMI radiated noise from the display shift clock.

Also the Spread Spectrum Clocking section of the TRM have a confusing note - the AM335x TRM says that LCD and MPU PLLs are only supported, while the AM437x TRM states that Display and MPU PLLs are supported. Then both TRMs go on the say that DISP PLL does not support SSC. As far as I can tell there are no LCD and Display PLLs, only DISP PLL. Which source can we use to enable SSC on the PRU clock?

In addition, all PLLs in the TRM have register CM_CLKMODE_DPLL_<PLL-NAME> (DISP, CORE, PER, MPU, DDR) that would allow SSC mode of operation. Do all PLLs can operate in SSC mode?

Thanks,

Kris