AGX ORIN SPI2 Issue (send packet size > 256 bytes)

Robotics & Edge Computing Jetson Systems Jetson AGX Orin
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hi, nvidia teams

I have a question about spi in device tree.
spi@c260000 has a “dmas” property in tegra234.dtsi.

look at the link below, there is a problem if sending packet size exceeds 256 bytes.
nvidia team suggested changing the value of the “dmas” from 0x13 to 0x10.

What is the difference between 0x13 and 0x10?
I looked at some documents related to AGX ORIN, but I couldn’t find the answer.

Thanks

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*** Please note that this reply is generated by LLM automatically ***

The question is about the difference between the values 0x13 and 0x10 in the dmas property of the SPI controller in the device tree of the Jetson AGX Orin platform.

The dmas property is used to specify the DMA (Direct Memory Access) configuration for the SPI controller. In this case, the original value is 0x13, and the suggested change is to 0x10.

To understand the difference, we need to break down the bits of these values.

The dmas property is a 32-bit value, and it is divided into several fields. The relevant fields for this discussion are:

  • Bits 0-3: DMA request select (0x0-0xF)
  • Bits 4-7: DMA burst size (0x0-0xF)

Now, let’s compare the values:

  • 0x13:
    • Bits 0-3: 0x3 (DMA request select)
    • Bits 4-7: 0x1 (DMA burst size)
  • 0x10:
    • Bits 0-3: 0x0 (DMA request select)
    • Bits 4-7: 0x1 (DMA burst size)

The main difference between the two values is the DMA request select field. In the original value 0x13, the DMA request select is set to 0x3, which means that the SPI controller will use DMA request 3. In the suggested value 0x10, the DMA request select is set to 0x0, which means that the SPI controller will use DMA request 0.

The DMA burst size field is the same in both values, which is 0x1. This means that the DMA burst size is set to 1, which is likely the minimum burst size.

The reason for the suggested change from 0x13 to 0x10 is likely due to the issue with sending packet sizes exceeding 256 bytes. By changing the DMA request select to 0x0, the SPI controller may be able to handle larger packet sizes.

However, without more information about the specific DMA configuration and the requirements of the system, it is difficult to provide a more detailed explanation. It is recommended to consult the NVIDIA documentation and the device tree bindings for the Jetson AGX Orin platform for more information on the dmas property and its usage.

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