Hi,

I'm working with a custom sound chip with its own DMA hardware. The figure shows how the I2S DMA expects data to be prepared:

IRQ1 +----------------+ | page_3 (right) |\ +----------------+ > double buffer 1 | page_2 (left) |/ IRQ0 +----------------+ | page_1 (right) |\ +----------------+ > double buffer 0 | page_0 (left) |/ +----------------+

The hardware has 2 double buffers, each containing left and right sample regions, i.e. it alternately transmits samples from page_0 and page_1, i.e. double buffer 0, then generates an interrupt and starts transmitting page_2 and page_3. After that another interrupt is generated and the process begins again with double buffer 0.

So my question is, how to tell ALSA about this memory layout? Is it possible to operate in MMAP mode with SNDRV_PCM_INFO_NONINTERLEAVED? But then, how to tell the application that it should either fill double buffer 0 or 1? Or should I use RW mode? Or something else?

Furthermore, since the hardware doesn't provide a 'current' DMA pointer containing the DMA address being transmitted at the moment (I only have interrupts generated after each double buffer has been transmitted), what should the pcm_pointer() callback return?

(I guess it should return 0 when called before IRQ0 and sizeof(double buffer 0) between IRQ0 and IRQ1?)

Best regards, Markus Korber