Sorry i messed it up, my apologies !
it sould be
void *buf[NUM];
> void *buf[NUM*BUFF_SIZE];
>
> buf [0] = mmap (fd, ...);
>
> for( i = 0; i < NUM; i++ ) {
> buf [1] = buf [0] +i* BUFF_SIZE; /* GCC extension :) */
>
>
> read( iofd, buf, NUM*BUFF_SIZE );
> /* Initially u fill in all buffers with data. */
>
>
>
configure_number_of_driver_buffers_and_kick_it_to_start_xfer_of_first_buffer
> ();
> /* This one kicks off the xfer of FIRST buffer */
>
> no = 0;
>
> for( index = 0; !done(); index = (index+1)%NUM ) {
>
> /* WAIT till u get an intimation (irq_handler) */
> /* This could be done by sem, fasync+sleep, or poll, */
> /* I used fasync() here with sleep */
>
> sleep(1);
> /* The sleep time is depending on the design,
> This fills up the buffer even if its not used up by driver
> bcoz, here the data xfered is video data, delay
> is more costly than data loss. So i can do with data loss
> than delay ( NOTE: this is true for MY application )
> */
> Here the driver itself switches to next buffer xfer in irq_handler.
>
> read( iofd, buff[index], BUFF_SIZE );
>
> }
>
> Well, the n buffers are required here bcoz of bandwidth and the
> limitation
> on size of DMA capable buffers available in linux kernel.
> u get buffers through __get_dma_pages() which can give u
> max 128k most of the times.
>
> Now considering the speed of CPU (mine is 233Mhz) and speed of DMA
100
> Mbps by the device ).
> The device can finish xfering the 1st buffer before u fill in the second
> one.
> So till its finished, u need to block ( Which is not prefered ).
> To give for this spead diffs u either need a very large buffer
> or increase number of small buffers.
> U can calculate the exact buff nos and size depending on calculations
> done on disk_read_latency, driver-appl switching latency,
> actual throughput of the device etc.
>
> -nagaraj.
> \(*_*)/
>
>
>
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