I am looking into the ES18XX driver for my ES1878.

Now, I get static when using only the second DMA channel, as dma1=5, dma2=5, and no other errors. (The firstDMA channel does not work at all…) My investigation points to that there may be problems in the sample rate/filter divider calculations.

Could any knowledgeable person verify if this calculation incorrect or not:

/* set filter register */
div0 = 256 - 7160000*20/(8*82*runtime->rate);

Here is the text outlining the procedure from the Datasheet for ES1878:

This register controls the low-pass frequency of the switchcapacitor
filters inside the ES1878. Generally, the filter rolloff
should be positioned at 80% - 90% of the Sample_Rate/
2 frequency. The ratio of the roll-off frequency to the filter
clock frequency is 1:82. In other words, first determine the
desired roll-off frequency by taking 80% of the
Sample_Rate divided by 2, then multiply by 82 to find the
desired Filter Clock frequency. Use the formula below to
determine the closest divider:
Filter_Clock_Frequency = 7.16 MHz / (256-Filter_Divider_Register)

Regards From Erik

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