Re: kernel threads etc

[Lee Revell <rlrevell@joe-job.com>]

On Tue, 2006-03-07 at 21:19 +0000, Adrian McMenamin wrote:
> 0. Create a DMA buffer in SH4 space - this is used as the source for
> the
> dma transfer (the target is in the ARM7's memory space). Alsa seems to
> fill up this buffer easily enough
> 
> 1. Fill the ring buffer completely with first DMA transfer (ring
> buffer
> has space for 8 periods) on receiving the SNDDRV_PCM_TRIGGER_START,
> then
> start the ARM7 playback
> 
> 2. ARM7 fires interrupt on SH4 bus every time period is played
> 
> 3. SH4 interrupt handler counts interrupts - have 4 elapsed? if yes
> then
> fill up first half of ring buffer - have 8 elapsed? then fill up
> second
> half
> 
> 4. However the data in the DMA buffer never seems to change - ie I
> just
> play the same 8 periods worth of sound, and the buffer never fills up
> with new material from the user space/application/alsa middle layer -
> and the calling app blocks ad infinitum, because clearly it is never
> told to send any more data
> 

You should be transferring one period of data every interrupt - why are
you transferring 4 at a time?

Lee



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