Hi,
I’m trying to get I2S2 and DMA working on a ezDSP5535 board am reading I2S frame-sync and overflow errors every time the HW ISR executes (I2SINTFL = 0x0003).
The I2S is configured as: stereo, packed, 16-bit word, master, left-justified, 1-bit delay. The PLL is configured to run the CPU at 98.304 MHz. The I2S clock is divided by 64 to give 1.536 MHz. The I2S frame sync divides the clock by 32 to give a 48 KHz frame rate.
DMA controller1 configuration is: ping/pong, auto reload, channels 0 and 1 are synchronized to I2S Tx events. Channel 0 handles I2S Tx left transfers channel 1 handles I2S Tx right transfers. DMA interrupts are only enabled for channel 1 (I2S right channel), as the I2S Tx sync event is triggered after the right-channel event occurs. The DMA interrupts occur after every 48 transfers – in theory, every 1 millisecond.
At the moment, no I2S Rx events are sync’d with DMA for debug purposes.
In my DMA HW ISR handler, I read the I2S INTFL register and also snapshot the current time with the BIOS CLK_gethtime(). I compute the delta-time between HW interrupts and save that info to a buffer. If the ISRs were happening at exactly 1 ms, I would expect the delta-time to be 0xC000 every time. Instead I’m measuring delta values that indicate dropped interrupt events. The timing shows a periodicity to the HW interrupt timing – about 8 consecutive interrupts that are ‘close to’ 1 ms but still beyond what I expect, then about 5 consecutive interrupts where the delta time is on the order of 2 ms. This pattern can be seen in the memory snapshot below: each row shows three variables saved-off in during my ISR: the left column is delta-time from the last ISR, the middle column is the dmaifr event, and the third column is a global counter variable that is incremented from a periodic timer function that executes at a 1-ms rate. When the delta-time indicates a missing interrupt, the global timer variable has incremented by 2.
The I2S2 CTRL register is programmed to 0x8092, ISSRATE register is programmed to 0x0015.
I’m at a loss as to what could be causing these timing fluctuations and missed interrupts. Does anyone have any suggestions?
Thanks,
Jim
0000BFD4 00000020 001DA604
0000BFCE 00000020 001DA605
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00016FFB 00000020 001DA621
000177F7 00000020 001DA623
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