Question on setting pd->length to same as pd->size

[nkolban]

In the sample code in the function called dma_desc_init() we find the creation of the DMA descriptors in a linked list. In the initialization of an element of this list, we find that we are creating and populating instances of lldesc_t structures.

In this structure we set (among others):

• buf - A pointer to a malloced RAM biffer of size=buf_size
• size - We record the size of the buffer (=buf_size)
• length - The sample code also sets this to be buf_size

This causes me to be puzzled. I understand that buf is the storage to be written into and I understand that size is the amount of storage that the DMA subsystem can write into. It is length that is causing me pause. I had understood that the value of this would be the length of data actually written into the buffer by DMA. At initialization time, I would thus have imagined that its value would be 0 as opposed to the size of the buffer itself. I would have thought that 0 would indicate that no bytes within the buffer have been utilized to store DMA retrieved data?

[igrr]

You are right, i think the value does not matter when I2S is writing data into the buffer. It would have mattered if I2S was reading data from the buffer. Will fix this.