ISELED clock configuration without SOSC

[ThijsK]

What are suitable clock setups for the ISELED component without using the external clock source (and thus without PLL source, and only with SIRC & FIRC) on a S32K144?

I've been searching the documentation, but I can't find good pointers

User guide (S32K1xxISELEDUG) gives some confusing information to me:

• The middle paragraph of Section 2.3 notes the limited accuracy of the internal RC oscillators. Does that mean the internal oscillator is not suitable?
• Section 3.1.2 highlights the XTAL interface, but doesn't say anything about it being recommended or required.
• Section 4.2.1 states a SYS_CLK of 80MHz and a BUS_CLK of 40MHz for a S32K144 as a typical configuration. What are typical configurations without SOSC?
• Figure 18 shows SIRC disabled, but Figure 20 shows Timer CLK as SIRCDIV2_CLK as its source. Also, the divisor values for weren't shown in Fig 18, so I can only guess what the actual frequencies are that go to the FlexIO peripheral.
• Section 4.2.2 says Timer CLK should be "consistent" with interface clock. Does that mean equal, or some specific ratio?

Presentation slide 14 from session AMF-AUT-T3817 (Allen Li, Oct. 2019) states internal oscillator should be feasible

There is nothing about valid clock sources, or ranges of input clock frequencies in the user manual of S32K1xx RTM 3.0.0 or the user guide of ISELED driver (v5.0, 2019)

#FS32K144ULT0VLHT

[Julián_AragónM · Accepted solution]

Hi @ThijsK,

1. The on-die oscillator described in chapter 2.3 refers to the INLC100Q16's clock circuitry:

And even though it does have limited accuracy, the whole system is designed for the +-30% variance, so there should be no issues with the on-die oscillator.

2. Section 3.1.2 showcases a hardware design reference for ISELED based on the S32K1xx family. This is the recommended circuitry also found in AN5426. It is simply the go-to reference design for an oscillator.

3. The only recommended clock configuration is as stated in chapter 4.2.1:

Since the ISELED driver also uses the FlexIO and SPI drivers, you can configure these two drivers from the MCU with any configuration. You can use AN5408 (S32K1xx Clock Calculator Guide) to help you design a clock configuration which fits your needs.

4. I think it would be better to import the example included in the ISELED driver and see the values assigned to each clock module, instead of guessing the clock dividers and configurations.

5. Consistent means that the Timer CLK should be equal to the interface clock. This is to ensure synchronization between the timer and the communication interface.

Even though this document describes the solution and how to integrate it with the S32K1xx devices, I would strongly suggest porting over to the newer RTD package instead of the older SDK; The ISELED team is not continuing to do maintenance or support for SDK ISELED anymore.

If you have further questions, please help me entering a support ticket instead of posting in the public forum.

Best regards,
Julián

[ThijsK]

hi Julián,

Thanks for the quick reply. I was worried that we needed the external oscillator for clock accuracy or a higher bus clock. I'm relieved that we can work with the FIRC.