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SPI slowing down in OMAP L-137

Radek Semerad
Prodigy 110 points
Other Parts Discussed in Thread: OMAPL138

Hi,

I have to slow down the SPI speed in OMAP L-137, where only PLL0 is present. Max. SPI1 CLK frequency 400kHz is required.

Is it really necessary to have fixed ratio SYSCLK2 = SYSCLK1 / 2?  

What would happen if SYSCLK2 = SYSCLK1 / 3?

Is the only possibility to slow down the CPU operating frequency (i.e. maximum SYSCLK1 = 2 *256 * 400kHz = 204.8MHz )?

Thank you.

Radek

  • 0
    TI__Guru** 116170 points

    Radek,

    On OMAPL137, the minimum and maximum SPI frequency is tied to the CPU operating freq. This as been described in the SPI timings in the datasheet. The SYSCLK2 which is the SPI module clock needs to maintain a fixed ratio of 1:2 with the SYSCLK1(CPU operating frequency) for normal operation as described in the system reference manual for the device. If you are still in the design stage, you should consider OMAPL138 part for the design as this part has two PLLs (PLL0,PLL1) and the SPI1 on the device can be optionally driven by PLL1 and allows for additional programmable clock dividers that can be configured to attain the lower frequencies that you hope to attain.

    If this is not possible, are there any other serial interfaces on the device you can consider for your design. Perhaps if you describe what you wish to perfornm using the SPI interface, we could suggest some options. Also note OMAPL137 can be configured to dynamically change the operating frequency, so if your design permits you could drop down the CPU clock to the lower frequency when SPI communication is required and drive it back up when the communication is done.

    Regards,

    Rahul

  • 0 in reply to Rahul Prabhu
    Prodigy 110 points

    Thank you for your reply.

    I use SPI interface for communication with SD card in SPI mode (because a SD card controller inside the microcontroller is not available due to EMIFA utilization). For initial SD card identification, max. 400KHz clock is required (acording to the SD card SPI mode specification). So, I could also ask the SDCard organization to explain these low speed data transfer at the beginning of SD card identifation...

    Radek