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TMS320F280049: Maximum speed of FSI used as SPI

Brian Wang0
Expert 5230 points
Part Number: TMS320F280049

Hi team,

A short question:

According to my knowledge, the fasted speed of SPI in F280049 is 100Mhz/4=25Mhz.

What about the SPI achieved FSI in SPI mode? Will this have a higher speed?

Thanks!

  • 0
    TI__Guru** 113755 points

    Hi Brian,

    Even though FSI interface can work at higher speed, there is SW overhead when used as SPI hence will not give higher thoughput hence would recommend to use actual SPI interface instead of SPI mode of FSI.

    Regards,

    Vivek Singh

  • 0 in reply to Vivek Singh
    TI__Expert 5230 points

    Hi Vivek,

    What do you mean by SW overhead? In fact, I went through the source code of fsi_ex11_spifsi_full_duplex, and I did not noticed obvious difference comparing to using other communication peripherals.

    What is the condition FSI is designed to work as SPI interface?

    Regards,

    Brian

  • 0 in reply to Brian Wang0
    TI__Guru 52020 points

    What Vivek mentioned is,

    Every time you send data through fsi in SPI mode and it is received at an Mcu using the SPI peripheral, it will be receiving the frame tag, user data, then it will receive the data it self, then the crc and so on. The over head of reading all of these in the SPI module of the receiving mcu will slow things down. Then when you want to send data, you have to first send the frame tag, user data and so on using your SPI module. The device with fsi in SPI mode will automatically read those without user interaction.

    Nima

  • 0 in reply to Nima Eskandari
    TI__Expert 5230 points

    Hi Nima,

    Thanks for your reply but I am still a little bit confused.

    In fact, my customer is trying to use SPI as the interface betweeen F280049 and an ethercat controller. Thus, they are expecting higher SPI speed than 25Mhz we supported. Regarding our Fsi can support 50Mhz, they would like to use FSI as SPI.

    I understand we need to transmitt some addtional information in additional to the data it self to follow the protocol of the receiver device. But it is not related to whether we are using SPI module or FSI in SPI mode is that correct? Did you mean SPI mode FSI will require addtional tranmitting than the SPI module?

    Besides, when we are talking about the transmitting speed(25M or 50M), we are mainly talking about the bit rate. If FSI is used SPI, will it still run at 50Mhz?

    Regards,

    Brian

  • 0 in reply to Brian Wang0
    TI__Guru 52020 points

    Okay now that I know your device setup I can make it more clear.

    You f28004x device will transmit data easily using fsi in SPI mode at 50 MHz

    Your ethercat controller will receive the data plus extra information like the tags and the crc using SPI. On the ethercat controller side you will have to parse the frame and grab the data.

    Nima Eskandari