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I2S decoder

Created Wed, 11 Sep 2013 14:07:43 +0000 by ecolomato

ecolomato

Wed, 11 Sep 2013 14:07:43 +0000

Hi all,

I'm trying to talk to an I2S audio decoder with my uC32 board, but i get in trouble with timers. Could anyone help me with an example that works on MPIDE.

Thanks!

majenko

Thu, 12 Sep 2013 15:15:50 +0000

What is the trouble you're having with timers? What can't you do, or what doesn't do what you want to do?

ecolomato

Fri, 13 Sep 2013 07:05:45 +0000

The problem refers to me! I'm not an expert and don´t understand timers and OC configuration. Even reading the manual. So with an example, i could do some tests to understand them better.

Thank you very much!

ecolomato

Fri, 13 Sep 2013 07:21:09 +0000

Sorry!

I need a 44100Hz pulse, another 64 times faster, and another 256 times faster. And then output serial 16bit data at 44100Hz*64. One pin for each signal. But above all this, i need the processor not to be so busy doing that, because it has some other tasks to do.

Thanks again!

majenko

Fri, 13 Sep 2013 07:49:17 +0000

Ah, so what you want is to drive a CODEC chip then?

The PIC32 has hardware support for that built in to the SPI interface. You should check out the data sheet for the Serial Peripheral interface and look at framed mode.

The only thing it can't do is generate the 256x clock needed by most CODEC chips. You might be able to do it with a timer / OC pair, but getting that kind of clock accuracy at high frequencies may be tricky. 11289600Hz is an odd value to try and generate from an 80MHz base clock. Dividing by 7 (PS=1:1, PR=7 OC=3) yields 11428571.43Hz, which may be as close as you can get, and that won't be exactly 50% duty either. You may be better off with an external clock circuit to generate that signal.

ecolomato

Fri, 13 Sep 2013 19:44:10 +0000

Thank you very much! If there is no other way, i'll try external clock. I found out this code for MPLAB. It's supposed to drive a CODEC? If so, how could I export this code to MPIDE for some testing? Sorry for the large "paste":

/********************************************************************* *

  •  PIC32MX Audio I2S Communication and Reference Clock Output
  • FileName: audio_i2s.c
  • Dependencies: plib.h
  •              test_sine.c
  • Processor: PIC32
  • Complier: MPLAB C32
  •              MPLAB IDE v8+
  • Company: Microchip Technology Inc.
  • Software License Agreement
  • The software supplied herewith by Microchip Technology Incorporated
  • (the ?Company?) for its PIC32 Microcontroller is intended
  • and supplied to you, the Company?s customer, for use solely and
  • exclusively on Microchip PIC32 Microcontroller products.
  • The software is owned by the Company and/or its supplier, and is
  • protected under applicable copyright laws. All rights are reserved.
  • Any use in violation of the foregoing restrictions may subject the
  • user to criminal sanctions under applicable laws, as well as to
  • civil liability for the breach of the terms and conditions of this
  • license.
  • THIS SOFTWARE IS PROVIDED IN AN ?AS IS? CONDITION. NO WARRANTIES,
  • WHETHER EXPRESS, IMPLIED OR STATUTORY, INCLUDING, BUT NOT LIMITED
  • TO, IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  • PARTICULAR PURPOSE APPLY TO THIS SOFTWARE. THE COMPANY SHALL NOT,
  • IN ANY CIRCUMSTANCES, BE LIABLE FOR SPECIAL, INCIDENTAL OR
  • CONSEQUENTIAL DAMAGES, FOR ANY REASON WHATSOEVER.
  • Platform: Explorer-16 with PIC32MX PIM
  • Description:
  •  The example generates 12.288MHz Reference Clock Output and

  •  is configured for 48kHz sample rate 24-bit I2S stereo

  •  communication. A sinusoid tone sampled at 48kHz is transmitted

  •  over I2S output. REFOCLK, SS, SDO and SDI pins use the

  •  Peripheral Pin Select functionality for flexible mapping of I2S

  •  functionality on desired pins. The readme file states the pins

  •  that can be probed to observe the I2S and Reference Clock Output

  •  signals.

********************************************************************/ #include <plib.h>

#if defined (32MX360F512L) || (32MX460F512L) || (32MX795F512L) || (32MX430F064L) // Configuration Bit settings // SYSCLK = 80 MHz (8MHz Crystal / FPLLIDIV * FPLLMUL / FPLLODIV) // PBCLK = 80 MHz (SYSCLK / FPBDIV) // Primary Osc w/PLL (XT+,HS+,EC+PLL) // WDT OFF // Other options are don't care #pragma config FPLLMUL = MUL_20, FPLLIDIV = DIV_2, FPLLODIV = DIV_1, FWDTEN = OFF #pragma config POSCMOD = HS, FNOSC = PRIPLL, FPBDIV = DIV_1 #define SYS_FREQ (80000000L)

#elif defined (32MX220F032D) || (32MX250F128D) // Configuration Bit settings // SYSCLK = 48 MHz (8MHz Crystal / FPLLIDIV * FPLLMUL / FPLLODIV) // PBCLK = 48 MHz (SYSCLK / FPBDIV) // Primary Osc w/PLL (XT+,HS+,EC+PLL) // WDT OFF // Other options are don't care #pragma config FPLLMUL = MUL_24, FPLLIDIV = DIV_2, FPLLODIV = DIV_2, FWDTEN = OFF #pragma config POSCMOD = HS, FNOSC = PRIPLL, FPBDIV = DIV_1 #define SYS_FREQ (48000000L) #endif

//Definitions. #define SAMPLE_RATE 48000 #define FRAME_SIZE (SAMPLE_RATE/1000) #define RODIV 3 #define REFTRIM 464

//Stereo audio structure for 24-bit I2S data.

typedef union {

struct {
    INT32 rightChannel;
    INT32 leftChannel;
};
UINT64 audioWord;

} AudioStereo; AudioStereo* txBuffer;

/* Main entry function */ int main(void) { UINT spi_con1 = 0, spi_con2 = 0; UINT baud_rate = SAMPLE_RATE * 64; UINT mclk = SAMPLE_RATE * 256; extern AudioStereo test_sine[];

//Congigure MIPS, Prefetch Cache module.
SYSTEMConfig(SYS_FREQ, SYS_CFG_WAIT_STATES | SYS_CFG_PCACHE);
INTEnableSystemMultiVectoredInt();

//Test tone vector sampled at 48kHz.
txBuffer = test_sine;

//Configure the direction of used pins and
//configure as digital pins.
#if defined (__32MX220F032D__) || defined (__32MX250F128D__)
PORTSetPinsDigitalOut(IOPORT_A, BIT_1);
PORTSetPinsDigitalOut(IOPORT_B, BIT_4);
PORTSetPinsDigitalIn(IOPORT_B, BIT_5);
PORTSetPinsDigitalOut(IOPORT_C, BIT_3);
#elif defined (__32MX430F064L__)
PORTSetPinsDigitalOut(IOPORT_D, BIT_9);
PORTSetPinsDigitalOut(IOPORT_D, BIT_15);
PORTSetPinsDigitalIn(IOPORT_D, BIT_3);
PORTSetPinsDigitalOut(IOPORT_D, BIT_4);
#endif

/*------------------------------------------------
Pin mapping for PIC32MX220F032D and PIC32MX250F128D:
--------------------------------------------------
Function	PPS	Pin#	Test Point#	: Comment
__________________________________________________________________________
REFOCLK(o)	RPC3	(36)	TP36		: Reference Clock Output
SCK1(o)	-	(14)	TP14            : SPI-I2S SCLK Output
SS(o)	RPB4	(33)	TP33            : SPI-I2S LRCK Output
SDO(o)	RPA1	(20)	TP20            : SPI-I2S SDO Output
SDI(i)	RPB5	(41)	-               : SPI-I2S SDI Input */
#if defined (__32MX220F032D__) || defined (__32MX250F128D__)
PPSOutput(3, RPC3, REFCLKO); //REFCLK0: RPC3 - Out
PPSInput(2, SDI1, RPB5); //SDI: RPB5 - In
PPSOutput(2, RPA1, SDO1); //SDO: RPA1 - Out
PPSOutput(1, RPB4, SS1); //SS: RPB4 - Out

/*------------------------------------------------
Pin mapping for PIC32MX430F064L:
--------------------------------------------------
Function	PPS	Pin#	Test Point#	: Comment
__________________________________________________________________________
REFOCLK(o)	RPD9	(69)	-		: Reference Clock Output
SCK1(o)	-	(70)	-               : SPI-I2S SCLK Output
SS(o)	RPD4	(81)	-               : SPI-I2S LRCK Output
SDO(o)	RPD15	(48)	-               : SPI-I2S SDO Output
SDI(i)	RPD3	(78)	-               : SPI-I2S SDI Input */
#elif defined (__32MX430F064L__)
PPSOutput(3, RPD9, REFCLKO); //REFCLK0: RPD9 - Out
PPSInput(1, SDI1, RPD3); //SDI: RPD3 - In
PPSOutput(2, RPD15, SDO1); //SDO: RPD15 - Out
PPSOutput(3, RPD4, SS1); //SS: RPD4 - Out
#endif

//Configure Reference Clock Output to 12.288MHz.
mOSCREFOTRIMSet(REFTRIM);
OSCREFConfig(OSC_REFOCON_USBPLL, //USB-PLL clock output used as REFCLKO source
        OSC_REFOCON_OE | OSC_REFOCON_ON, //Enable and turn on the REFCLKO
        RODIV);

//Configure SPI in I2S mode with 24-bit stereo audio.
spi_con1 = SPI_OPEN_MSTEN | //Master mode enable
        SPI_OPEN_SSEN | //Enable slave select function
        SPI_OPEN_CKP_HIGH | //Clock polarity Idle High Actie Low
        SPI_OPEN_MODE16 | //Data mode: 24b
        SPI_OPEN_MODE32 | //Data mode: 24b
        SPI_OPEN_MCLKSEL | //Clock selected is reference clock
        SPI_OPEN_FSP_HIGH; //Frame Sync Pulse is active high

spi_con2 = SPI_OPEN2_AUDEN | //Enable Audio mode
        SPI_OPEN2_AUDMOD_I2S; //Enable I2S mode



//Configure and turn on the SPI1 module.
SpiChnOpenEx(SPI_CHANNEL1, spi_con1, spi_con2, (mclk / baud_rate));

//Enable SPI1 interrupt.
INTSetVectorPriority(INT_SPI_1_VECTOR, INT_PRIORITY_LEVEL_4);
INTSetVectorSubPriority(INT_SPI_1_VECTOR, INT_SUB_PRIORITY_LEVEL_0);
INTEnable(INT_SPI1, INT_ENABLED);

SpiChnPutC(SPI_CHANNEL1, 0); //Dummy write to start the SPI

//Idle.
while (1);

return 1;

}

/* SPI1 ISR */ void __ISR(_SPI_1_VECTOR, ipl4) SPI1InterruptHandler(void) { static UINT ptrIndex = 0; static BOOL toggleData = TRUE;

SpiChnPutC(SPI_CHANNEL1,
        (toggleData ? txBuffer[ptrIndex].leftChannel : txBuffer[ptrIndex++].rightChannel));
toggleData = !toggleData;
if (ptrIndex &gt;= FRAME_SIZE)
    ptrIndex = 0;
INTClearFlag(INT_SPI1TX);

}

majenko

Fri, 13 Sep 2013 20:54:24 +0000

With great difficulty. All that code uses the Microchip Peripheral Libraries. I am not sure what of those is available in MPLAB, if any. I know there was a move away from plib a bit back.

Pretty much all the function calls do is modify the SFRs, so if you read through section 23 of the reference manuals you should be able to work out which registers it is setting in what way, and emulate that by directly manipulating those registers.

I have never used the reference clock - I am not sure which chips in the PIC32 family have it, but it might well be the way to go for the 256x oversampling clock.

ecolomato

Mon, 30 Sep 2013 19:06:19 +0000

Sorry for the delay...

Now i'm following your advice of using an external clock. I've learned a bit on SFR's manipulating... ;) But can't find the way counting an external pulses to obtain the 256x sync. There is only one timer a could use (Timer1) to be external triggered on UNO32 or uC32 (soldering wires, of course). There's no TxCK pin available!!!! After setting Timer1 for external clock and apply clock source, TMR1 register remains 0x0 forever and ever.

Is there any other way?

Thanks!

ecolomato

Wed, 02 Oct 2013 12:11:29 +0000

Now i'm working with SFR's, got to say that is better than working with libraries. That is the only way to know what to are exactly doing. And you can do it from MPIDE as well as MPLAB. I managed to synchronize UNO32 (master) with an audio codec (slave) connecting the codec MCLK out to the secondary oscilator crystal hole.

Thanks again!!!