Description of DMA "sosf" field missing in technical reference manual

[kolban]

When working with DMA (in my case I2S), I see that there is a data structure that represents a linked list of buffers. See section 6.3.2 of the ESP32 technical references manual. When I compare this against the data structure called "lldesc_t", I find that there is a mysterious additional bit field called "sosf" which seems to be described as "start of sub frame". My question/puzzle is "What does this mean?" I can't seem to find any description of this concept within the documentation.

[ESP_Sprite]

From memory, I2S doesn't use that bit. The DMA engine of most peripherals are based on the same design, and some of them (the WiFi ones, for example) need subframes as well, hence the bit.

[BuddyCasino]

I don't know what that is, so I searched for "DMA subframe", yet couldn't find a decent explanation. Do you have a link or something?

[Baldhead]

If I2S "sosf" does not use this bit, why in the link below is this bit set ???

https://github.com/espressif/esp-iot-so ... lcd.c#L106