topic S32K146:LPSPI Register TCR->PRESCALE in S32K

S32K146:LPSPI Register TCR->PRESCALE

ShaoTianzhi — Wed, 06 Sep 2023 08:32:54 GMT

Hello:

Recently, while studying the code, I found a problem,I set LPSPI2_CLK to 32MHz

But when I configure LPSPI2, the source clock is actually writable.

And, I haven't seen any operations to get the clock source frequency in both the LPSPI_DRV_MasterConfigureBus and LPSPI_SetBaudRate functions. Finally, when I set the Baud rate to 4MHz, the prescaler register responsible for dividing the clock (TCR->PRESCALE) was set to 0x000h, which means no division, while my understanding is that its value should be 011b, corresponding to an 8x divider. Later, I tried to change the source clock to 4MHz, but TCR->PRESCALE remained 0.

I'd like to understand the relationship between the TCR->PRESCALE register, "Baudrate", "source clock", and the "LPSPI2_CLK" configuration. How is the code arriving at a TCR->PRESCALE value of 0, and what significance does setting 'LPSPI2_CLK' have? How does it differ from or relate to the "source clock"?

Re: S32K146:LPSPI Register TCR->PRESCALE

Senlent — Thu, 07 Sep 2023 03:16:19 GMT

Hi@ShaoTianzhi

1. The Baudrate here is actually the expected Baudrate
LPSPI_SetBaudRate()
This function will calculate an optimal frequency division value according to the expected baud rate you input and the module clock: tcrPrescaleValue

The following function is the function to set the TCR register:
LPSPI_SetTxCommandReg();

2.Source clock

It should be consistent with the clock configuration value in the frist picture you provided.

Re: S32K146:LPSPI Register TCR->PRESCALE

ShaoTianzhi — Thu, 07 Sep 2023 05:29:51 GMT

Why, when I set the source clock to 32MHz and the Baud rate to 4MHz, do I see that the calculated value for tcrPrescaleValue is 0 instead of 3 when I check in Debug mode?

Re: S32K146:LPSPI Register TCR->PRESCALE

Senlent — Thu, 07 Sep 2023 07:04:34 GMT

Hi@ShaoTianzhi

for SPI master mode:

baudrate should equal to : functional clock / (TCR->PRESCALE) / (CCR->SCKDIV + 2)

for example: clock source is 32Mhz, 4M baudrare

test result:

TCR->PRESCALE = 0 -> Divide by 1

CCR->PRESCALE = 0x06

baudrate = 32 / 1 / (0x06 + 2) = 4Mhz.

Re: S32K146:LPSPI Register TCR->PRESCALE

ShaoTianzhi — Thu, 07 Sep 2023 07:44:04 GMT

Thank you for your answer.