I2S Microphone and K22F

[eduardoumana]

I am trying to set up the INMP441 digital I2S microphone with the Kinetis K22F Freedom Board. The microphone data sheet is at:

http://www.invensense.com/mems/microphone/documents/INMP441.pdf

I have been able to implement the correct settings for the Bit Clock and Frame Sync (64 clocks per frame, 2 words per frame, etc...) through the 5 I2Sx_RCR registers. I am now trying to quickly obtain data from the microphone but have not been successful. Here is my code.

    CHIPEN = 1;

    L = 1;

    //Pins Init

    SIM_SCGC5 |= 0x42B82;       //Enables PORTC

    PORTC_PCR5 |= 0x400;        //PTC5 --> I2S0_RXD0 -> DATA (coming from Microphone)

    PORTC_PCR7 |= 0x400;        //PTC7 --> I2S0_RX_FS -> FRAME (Sent to Microphone)

    PORTC_PCR9 |= 0x400;        //PTC9 --> I2S0_RX_BCLK -> BITCLOCK (Sent to Microphone)

    //Clock Init

    SIM_SCGC6 |= 0x8000;            //Turn on I2S Clock Gate

    SIM_SOPT2 |= 0x30000;           //I2S Clocking Sourced from 48MHz IRC48MCLK

    I2S0_MCR |= 0x43000000;      //Output Enable. Mux IRC48MCLK into Fractional Divider

    I2S0_RCR2 |= 0x4000000;       //MCLK MSEL to BCLK

    I2S0_MDR |= 0x1F07C;            //Set I2S Master Clock to 12.2880MHz

    I2S0_RCR2 |= 0x300000D;       //DIV is 13 - > 9000kHz Sample Rate. BCD = 1

    SIM_SCGC6 |= 0x8000;             //Re-Enable I2S Module

    //Receive Init

    I2S0_RCSR = 0x0;                      //Disable Receive as per Datasheet

    I2S0_RCR1 |= 0x1;                    //Sets FIFO Watermark to 1

    I2S0_RCR3 |= 0x10000;            //Enable Receive Data Channel

    I2S0_RCR4 |= 0x11F19;            //Internal Frame Sync. Early Frame Sync. 32 SYWD. FRSZ 2.

    I2S0_RCR5 |= 0x1F1F1F00;       //32 Bits per Word. 32 Bits in First Word. Shifted 32.

    I2S0_RCSR = 0x2000000;          //FIFO Reset

    I2S0_RCSR |= 0x80000100;       //Enable and FIFO Enable

while(1) {

        if(I2S0_RCSR & 0x10000){

            pr(&I2S0_RDR0);               //Reads content from data register, problem is that is constantly 0

            led_red = 0;

        }

    }

}

The problem is that the I2S0_RDR0 register is stuck at 0. So evidently I am not getting data from the microphone. Any ideas? (The microphone is indeed sending data on the right channel as confirmed with an oscilloscope)

[xiangjun_rong]

Hi, Eduardo,

has your issue fixed yet? If not, can you use interrupt mechanism to read the I2S0_RDR0 without FIFO?

BR

XiangJun Rong

[eduardoumana · Accepted solution]

The FIFO was overflowing, an error flag was raised and never cleared so the FIFO didn't accept more data. The fix is setting FCONNT and clearing the error:

if(I2S0_RCSR & 0x10000){

            pr(&I2S0_RDR0); 

            led_red = 0;

        }       

        if (I2S0_RCSR & 0x20000){

            I2S0_RCSR |= 0x20000;

        }

[eduardoumana]

Some updates: The FIFO request flag is going high, so I am able to read I2S0_RDR0. However, the FIFO then overflows. The FIFO error flag rises.

Any hints as to how to keep the FIFO from overflowing?

[xiangjun_rong]

Hi, Eduardo,

As you know that the RFW bits in I2Sx_RCR1 register specifies the watermark level, for example, if you set RFW bits as 3, once the FRF bit in I2Sx_RCSR register is set, you can read the I2S0_RDR register 4 times to empty the FIFO.

BR

XiangJun Rong

[xiangjun_rong]

Hi, Eduardo,

Regarding your question, I do not think you have the code to poll the status register to check if the I2S has received the data, then read the I2S0_RDR0 register.

how about using the code:

    while(1){

       //  wait(0.01);

     if(I2S0_RCSR&0x10000) //check the FIFO Request Flag

{

         pr(&I2S0_RDR0);  //Prints register address and contents

         led_red = 0;

    }

I do not debug your code, pls have a try to test the code.

BR

XiangJun Rong

[eduardoumana]

Unfortunately that didn't work. The FIFO request flag is not raised, so the contents of I2S0_RDR0 are never read.

I think the issue is the micro controller not "interpreting/receiving" the data because the microphone is indeed sending it. Two possible issues come to mind:

1) The data from the microphone should be connected to I2S0_RDX0, right?

2) The data sheet talks about enabling the receive channel to access the FIFO. Am I forgetting to enable a channel, a FIFO or something along those lines?