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Which Tools Can Emulate an SPI Slave Device without Inter-Byte Delay?
Rena Ayeras

Question from the Customer:

I need to emulate an SPI slave device that operates at 4 MHz. I am looking at the Promira Serial Platform and the applications. Would the SPI Active - Level 1 Application fulfill these requirements?

  • The data packet is 40 bits in length.
  • There is no inter-byte delay during 1 CS active event: 5 bytes continuously clocked out.
Response from Technical Support:

Thanks for your question! In summary, the Promira platform supports bitrates from 31 kHz to 80 MHz, and data can be delivered without inter-byte delay. With the SPI Active - Level 1 Application, the maximum bitrate in slave mode is 8 MHz so your bus speed of 4 MHz is supported. Detailed capabilities are provided in the following sections.

Transmitting Data Packets

The data transmission to the Promira platform occurs through a buffer. The implementation uses buffer sizes of 2 MB less 1 byte (2 MB – 1 B) for sending and receiving transactions as an SPI master or an SPI slave.

  • The maximum data size of single command is 1 MB.
  • The maximum amount of data in a queue is 64 MB – 1 B.

Packets in Slave Mode

Continuous Data. The word size can be set from 2 bytes to 32 bytes without inter-byte delay. For continuous data, assert Slave Select (SS) for the entire transaction.

The maximum amount of slave data to collect is 2 MB -1 B. To avoid losing data, we recommend collecting the SPI slave data as soon as possible.

Speed and Latency

Here is additional information, which can be important for the system interface of your setup.

For many reasons, latency occurs. For example, the Promira Software API and the computer operating system (OS) may add delay due to internal overhead. The Promira platform also has latency caused by the Ethernet/USB link to the computer. Although rare, there can be also delays across the Ethernet/USB bus within a transaction. There are methods to reduce latency:

  • The USB round-trip latency is reduced to 250us when using the High-speed USB over Ethernet connectivity.
  • The duration of the USB round-trip latency is further reduced when using Ethernet connectivity.
  • The Promira platform also supports API queuing, which may provide additional speed-up.
  • Although rare, delays may occur with the Ethernet/USB bus within a transaction. For more information, please refer to SPI Signaling Characteristics section of the Promira Serial Platform I2C/SPI Active User Manual.

We hope this answers your questions. Additional resources that you may find helpful include the following:

If you want more information, feel free to contact us with your questions, or request a demo that applies to your application.

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