AM2431: Setting up MCSPI bit rates

Rajeev Bharol

Part Number: AM2431

Hi experts,
I am working on AM243 processor (ALV footprint) and am using Code Composer Studio version 12.1.0.00007 and SDK version mcu_plus_sdk_am243x_08_03_00_18

We have to run MCSPI port at 15 Mhz and when I set the bit rate to be 15000000 in example.syscfg settings for MCSPI, actually generated frequency is approximately 12.5 MHz. How can set the SPI bit rate to be exactly 15Mhz?

Thanks

Rajeev

over 2 years ago

0 Ming Wei over 2 years ago

TI__Guru 55145 points

Hi Rajeev,

Unfortunately, the bit rate has to be integer divisible of the input clock (50Mhz). To get the 15Mhz for the bit rate, you will have to use either 60Mhz (/4) or 45Mhz (/3) for the MCSPI input clock frequency.

Best regards,

Ming

0 Rajeev Bharol over 2 years ago in reply to Ming Wei

Prodigy 90 points

Hi Ming,
Thanks for the response.
How do I set the input clock frequency? It is automatically set to 50 MHz in auto-generated code in ti_drivers_config.c file.

0 Ming Wei over 2 years ago in reply to Rajeev Bharol

TI__Guru 55145 points

Hi Rajeev,

I looked into the AM243x TRM The MCSPI0 functional clock input is the MAIN_SYSCLK0/10. The syscfg is set to 50Mhz. That is saying it should not be changed.

Best regards,

Ming

0 Rajeev Bharol over 2 years ago in reply to Ming Wei

Prodigy 90 points

Hi Ming
Thankyou for the response.
Does it mean we can't achieve 15Mhz SPI bit rate on this part?

0 Ming Wei over 2 years ago in reply to Rajeev Bharol

TI__Guru 55145 points

Hi Rajeev,

You are correct. The closest one will be 16.67Mhz(50/3) or 12.25Mhz (50/4).

Best regards,

Ming

0 Hong Zhang over 2 years ago in reply to Ming Wei

Intellectual 782 points

Hello Ming,

What is the MAIN_SYSCLK0 number? Could we possibly scale this up?

Could we set the input clock to be other value instead of 50MHz? Like MAIN_SYSCLK0/4?

Thanks,

Hong

0 Ming Wei over 2 years ago in reply to Hong Zhang

TI__Guru 55145 points

Hi Hong,

MAIN_SYSCLK0 is 500Mhz.

I think it is not possible to scale up the MAIN_SYSCLK0, but you should be able to scale down it. It will affect your whole system performance if you scale it down.

Best regards,

Ming

0 Hong Zhang over 2 years ago in reply to Ming Wei

Intellectual 782 points

Hello Ming,

What are the options for MAIN_SYSCLK0?

Thanks,

Hong

0 Ming Wei over 2 years ago in reply to Hong Zhang

TI__Guru 55145 points

Hi Hong,

MAIN_SYSCLK0 has to be integer divisible of 2000Mhz (default is /4)

You can play with the PLL0 (MAIN PLL) with PLLCTRL0:

However, we do not recommend this, because the MAIN_SYSCLK0 will affect 60% - 70% of the peripherals. 500Mhz is the verified default value.

Best regards,

Ming

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AM2431: Setting up MCSPI bit rates