Hi, I posted the following question/mail to the ALSA development mailing list and somebody suggested posting it to the LKML, but I thought, perhaps it is better to ask you, the Linux PPC embedded experts first, since it is right about that topic.
It would be nice if somebody can say, if the described architecture makes sense and will work or if it is a complete no-go. -------- Forwarded Message -------- From: Joachim Förster <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Subject: [alsa-devel] embedded sound architecture question Date: Wed, 09 May 2007 22:47:34 +0200 Hi ALSA devs, I'm going to write an ALSA driver for a not yet existing AC97 controller, which is going to be "written" (VHDL), too (at the same time). Platform/Board is a Xilinx ML403 with Virtex-4 FPGA, PowerPC 405 architecture, OPB/OCP bus, AC97 Codec LM4550. Before presenting my question, I have to say, that I'm a beginner with ALSA/Linux driver development. My question is: Does the architecture described below make sense/is reasonable with ALSA and Linux? The problem is, that there is no DMA controller and implementing an OPB master device which would be able to do DMA itself is not an option at this time. So our thoughts were: Integrate the "DMA ring buffer" (which is usually somewhere in main memory/RAM) into the AC97 controller. Make ALSA access this HW buffer as if it was in main memory. This way, the device (AC97 controller) has "direct access" to its buffer "memory" - this could be called "fake DMA". The AC97 controller would have tell us where it is while playing and firing interrupts after one period, so that we don't write to values which are in the current period, instead update the area where of the past played periods etc. ... The buffer should be a "ring buffer", right? Mapping this "IO memory" into kernel space should be possible with io_remap_page_range(), right? I would have to implement the mmap() callback in my driver, to setup the given VMA (with the above function), right? So, ALSA library/applications will be able to use MMAP mode, which is what we want to achieve? [We don't want copy()/silence(). An intermediate buffer with ack()/tasklet/workqueue + FIFO in HW would be an alternative.] [snip] Thanks for reading & your time, Joachim _______________________________________________ Linuxppc-embedded mailing list Linuxppc-embedded@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-embedded
