S32K144 SPI baudrate

[lyz]

How do caculate S32K144 SPI Baudrate. How is computational formula？I see that in SDK. As fllow:

realBaudrate = (sourceClockInHz / (s_baudratePrescaler[prescaler] * (scaler + (uint32_t)2U)));

but， I do not understand. please tell me how is computational formula! thanks.

[VaneB · Accepted solution]

Hi @lyz 

The SPI baud rate is calculated as:

Baud Rate = (Functional clock / PRESCALE) / (SCKDIV+2)

PRESCALE: Configured in the Transmit Command Register (TCR).

SCKDIV: Configured in the Clock Configuration Register (CCR).

If you find the SDK implementation confusing, refer to section 2.8 of the S32K1xx Series Cookbook. It is a good starting point for understanding how to configure the LPSPI.

BR, VaneB

[lyz]

Project from example config delay in SDK, as follow. Why? I do not understand:

  

in S32K1xx Series Cookbook.

so,

How config SCKPCS of SCK-to-PCS Delay？

How config PCSSCK of PCS-to-SCK Delay？

How config DBT of Delay Between Transfers？

[VaneB]

Hi @lyz 

The bestScaler is used to configure delay registers because these delays scale with the SPI clock. Applying a right shift by 2 (>> 2U, equivalent to dividing by 4) ensures the delay values remain proportional to the baud rate without being excessively large, providing balanced timing margins for PCS-to-SCK, SCK-to-PCS, and Delay Between Transfers.

[lyz]

hello, @VaneB 

    Project from example config delay in SDK, as follow

the logic (>> 2U, equivalent to dividing by 4) refence where describe, Why?

I fell that it is diffent the logic whitch the reference of S32K-RM.pdf provide, as follow:

I do not understand!

What is the configuration logic, about SCKPCS / PCSSCK / and PCSSCK ? 

Please tell me.

Thank you very much!

[VaneB]

Hi @lyz 

The use of >> 2U (equivalent to dividing by 4) for delay calculations is not documented in the reference manual as a strict formula. Instead, it originates from SDK timing guidelines intended to ensure proper functionality.

[lyz]

I understand logic in SDK code, but the logic (>> 2U, equivalent to dividing by 4) refence where describe. The reference of S32K-RM.pdf provide of the logic, as follow:

so, What is the configuration logic, about SCKPCS / PCSSCK / and PCSSCK ?

How config SCKPCS of SCK-to-PCS Delay？

How config PCSSCK of PCS-to-SCK Delay？

How config DBT of Delay Between Transfers

in detail.

[lyz]

ok, thank you. 

[lyz]

 I do not understand these:

The SCK period is equal to (SCKDIV+2) cycles of the LPSPI functional clock divided by the Prescaler Value TCR[PRESCALE] configuration.

realBaudrate = (sourceClockInHz / (s_baudratePrescaler[prescaler] * (scaler + (uint32_t)2U)));