Which SPI Host Adapter Works Best to Interface with an MCU Device for High Speed Framing with DMA Enabled?

Question from the Customer:

I am interfacing a TI MCU (TM4C129x series) with the Aardvark SPI/I2C Host Adapter configured to slave mode. The MCU is sending 10 bytes consecutively out its SPI port in a single frame forming a single message (slave select signal is asserted for the entire 10 byte frame). The clock rate is 2 MHz.

I have observed that the Aardvark adapter is dropping some of these bytes. Looking at the Aardvark User Manual, I see there is a 4 us delay between each byte in a frame. Is there any way around this?

Also, I don't see a way to insert a delay in the output stream from the MCU without disabling DMA, which I need for this setup, as well as the high speed framing.

Can the Cheetah SPI Host Adapter meet these timing requirements - receive 8-byte messages without any delays between bytes?

Response from Technical Support:

Thanks for your questions!  For your application, we recommend the Promira Serial Platform with the SPI Active -Level 1 Application.  In SPI slave mode, the Promira platform can send multiple SPI bytes without delay in one transaction when SS is asserted for the entire transaction.  The Aardvark adapter’s slave speed will not meet your requirement and the Cheetah adapter functions as a SPI master only.

The SPI signaling diagram and bullet points below compares the setup timing of the Promira platform and the Aardvark adapter and may help shed some light on the subject:

SPI Byte Waveform for SS, MOSI and MISO signals Figure 1: SPI Byte Timing (td is setup time)

 

  • For the Promira platform, the SPI slave setup time is 0 μs.
  • For the Aardvark adapter, the SPI slave setup time is 7-9 μs.

Since the Promira platform has 0 set up time, it will be able to receive all the bytes in the entire SPI frame. For more information about the Promira platform SPI signal characteristics, please refer to section 6.2.1 of the Promira Serial Platform User Manual. For more information about the Aardvark adapter SPI signal characteristics, please refer to section 2.4 of the Aardvark I2C/SPI Host Adapter User Manual.

The Promira platform is an advanced serial device. In addition to meeting your timing specifications, the Promira platform supports:

  • High speed master/slave programming, up to 1 MHz I2C and 12.5 MHz SPI
  • Level shifting 0.9 V – 3.3 V
  • USB 2.0/Ethernet connectivity

The features of the Promira platform are expandable - applications can be downloaded. Today, both I2C Active - Level 1 and SPI Active – Level 1 applications are available.  Additional applications for the Promira platform are scheduled to be released within the next quarter. New features will include higher I2C and SPI speeds, quad and dual I/O, and additional protocols.

Additional resources that you may find helpful include the following:

We hope this answers your questions. If you have other questions about our host adapters or other Total Phase products, feel free to email us at sales@totalphase.com, or if you already own one of our devices and have a technical question, please submit a request for technical support.

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