annotate pru_rtaudio.p @ 39:638bc1ae2500 staging

Improved readibility of the DIGITAL code in the PRU, using register names instead of aliases and expanding some of the macros, removing unused macros. Binaries were not modified

.origin 0
.entrypoint START

#define DBOX_CAPE	// Define this to use new cape hardware
	
#define CLOCK_BASE  0x44E00000
#define CLOCK_SPI0  0x4C
#define CLOCK_SPI1  0x50
#define CLOCK_L4LS  0x60

#define SPI0_BASE   0x48030100
#define SPI1_BASE   0x481A0100
#define SPI_BASE    SPI0_BASE
	
#define SPI_SYSCONFIG 0x10
#define SPI_SYSSTATUS 0x14
#define SPI_MODULCTRL 0x28
#define SPI_CH0CONF   0x2C
#define SPI_CH0STAT   0x30
#define SPI_CH0CTRL   0x34
#define SPI_CH0TX     0x38
#define SPI_CH0RX     0x3C
#define SPI_CH1CONF   0x40
#define SPI_CH1STAT   0x44
#define SPI_CH1CTRL   0x48
#define SPI_CH1TX     0x4C
#define SPI_CH1RX     0x50

#define GPIO0 0x44E07000
#define GPIO1 0x4804C000
#define GPIO_CLEARDATAOUT 0x190
#define GPIO_SETDATAOUT 0x194

#define PRU0_ARM_INTERRUPT 19

#define C_ADC_DAC_MEM C24     // PRU0 mem
#ifdef DBOX_CAPE
#define DAC_GPIO      GPIO0
#define DAC_CS_PIN    (1<<5) // GPIO0:5 = P9 pin 17
#else
#define DAC_GPIO      GPIO1
#define DAC_CS_PIN    (1<<16) // GPIO1:16 = P9 pin 15
#endif
#define DAC_TRM       0       // SPI transmit and receive
#define DAC_WL        32      // Word length
#define DAC_CLK_MODE  1       // SPI mode
#define DAC_CLK_DIV   1       // Clock divider (48MHz / 2^n)
#define DAC_DPE       1       // d0 = receive, d1 = transmit

#define AD5668_COMMAND_OFFSET 24
#define AD5668_ADDRESS_OFFSET 20
#define AD5668_DATA_OFFSET    4
#define AD5668_REF_OFFSET     0

#ifdef DBOX_CAPE
#define ADC_GPIO      GPIO1
#define ADC_CS_PIN    (1<<16) // GPIO1:16 = P9 pin 15
#else
#define ADC_GPIO      GPIO1
#define ADC_CS_PIN    (1<<17) // GPIO1:17 = P9 pin 23
#endif
#define ADC_TRM       0       // SPI transmit and receive
#define ADC_WL        16      // Word length
#define ADC_CLK_MODE  0       // SPI mode
#define ADC_CLK_DIV   1       // Clock divider (48MHz / 2^n)
#define ADC_DPE       1       // d0 = receive, d1 = transmit

#define AD7699_CFG_MASK       0xF120 // Mask for config update, unipolar, full BW
#define AD7699_CHANNEL_OFFSET 9      // 7 bits offset of a 14-bit left-justified word
#define AD7699_SEQ_OFFSET     3      // sequencer (0 = disable, 3 = scan all)

#define SHARED_COMM_MEM_BASE  0x00010000  // Location where comm flags are written
#define COMM_SHOULD_STOP      0		  // Set to be nonzero when loop should stop
#define COMM_CURRENT_BUFFER   4           // Which buffer we are on
#define COMM_BUFFER_FRAMES    8           // How many frames per buffer
#define COMM_SHOULD_SYNC      12          // Whether to synchronise to an external clock
#define COMM_SYNC_ADDRESS     16          // Which memory address to find the GPIO on
#define COMM_SYNC_PIN_MASK    20          // Which pin to read for the sync
#define COMM_LED_ADDRESS      24          // Which memory address to find the status LED on
#define COMM_LED_PIN_MASK     28          // Which pin to write to change LED
#define COMM_FRAME_COUNT      32	  // How many frames have elapse since beginning
#define COMM_USE_SPI          36          // Whether or not to use SPI ADC and DAC
#define COMM_NUM_CHANNELS     40	  // Low 2 bits indicate 8 [0x3], 4 [0x1] or 2 [0x0] channels
#define COMM_USE_DIGITAL  44	  // Whether or not to use DIGITAL

#define MCASP0_BASE 0x48038000
#define MCASP1_BASE 0x4803C000

#define MCASP_PWRIDLESYSCONFIG 		0x04
#define MCASP_PFUNC			0x10
#define MCASP_PDIR			0x14
#define MCASP_PDOUT			0x18
#define MCASP_PDSET			0x1C
#define MCASP_PDIN			0x1C
#define MCASP_PDCLR			0x20
#define MCASP_GBLCTL			0x44
#define MCASP_AMUTE			0x48
#define MCASP_DLBCTL			0x4C
#define MCASP_DITCTL			0x50
#define MCASP_RGBLCTL			0x60
#define MCASP_RMASK			0x64
#define MCASP_RFMT			0x68
#define MCASP_AFSRCTL			0x6C
#define MCASP_ACLKRCTL			0x70
#define MCASP_AHCLKRCTL			0x74
#define MCASP_RTDM			0x78
#define MCASP_RINTCTL			0x7C
#define MCASP_RSTAT			0x80
#define MCASP_RSLOT			0x84
#define MCASP_RCLKCHK			0x88
#define MCASP_REVTCTL			0x8C
#define MCASP_XGBLCTL			0xA0
#define MCASP_XMASK			0xA4
#define MCASP_XFMT			0xA8
#define MCASP_AFSXCTL			0xAC
#define MCASP_ACLKXCTL			0xB0
#define MCASP_AHCLKXCTL			0xB4
#define MCASP_XTDM			0xB8
#define MCASP_XINTCTL			0xBC
#define MCASP_XSTAT			0xC0
#define MCASP_XSLOT			0xC4
#define MCASP_XCLKCHK			0xC8
#define MCASP_XEVTCTL			0xCC
#define MCASP_SRCTL0			0x180
#define MCASP_SRCTL1			0x184
#define MCASP_SRCTL2			0x188
#define MCASP_SRCTL3			0x18C
#define MCASP_SRCTL4			0x190
#define MCASP_SRCTL5			0x194
#define MCASP_XBUF0			0x200
#define MCASP_XBUF1			0x204
#define MCASP_XBUF2			0x208
#define MCASP_XBUF3			0x20C
#define MCASP_XBUF4			0x210
#define MCASP_XBUF5			0x214
#define MCASP_RBUF0			0x280
#define MCASP_RBUF1			0x284
#define MCASP_RBUF2			0x288
#define MCASP_RBUF3			0x28C
#define MCASP_RBUF4			0x290
#define MCASP_RBUF5			0x294
#define MCASP_WFIFOCTL			0x1000
#define MCASP_WFIFOSTS			0x1004
#define MCASP_RFIFOCTL			0x1008
#define MCASP_RFIFOSTS			0x100C

#define MCASP_XSTAT_XDATA_BIT           5        // Bit to test for transmit ready
#define MCASP_RSTAT_RDATA_BIT           5        // Bit to test for receive ready 
	
// Constants used for this particular audio setup
#define MCASP_BASE 	MCASP0_BASE
#ifdef DBOX_CAPE
#define MCASP_SRCTL_X	MCASP_SRCTL2	// Ser. 2 is transmitter
#define MCASP_SRCTL_R	MCASP_SRCTL0	// Ser. 0 is receiver
#define MCASP_XBUF	MCASP_XBUF2
#define MCASP_RBUF	MCASP_RBUF0
#else
#define MCASP_SRCTL_X	MCASP_SRCTL3	// Ser. 3 is transmitter
#define MCASP_SRCTL_R	MCASP_SRCTL2	// Ser. 2 is receiver
#define MCASP_XBUF	MCASP_XBUF3
#define MCASP_RBUF	MCASP_RBUF2
#endif
	
#define MCASP_PIN_AFSX		(1 << 28)
#define MCASP_PIN_AHCLKX	(1 << 27)
#define MCASP_PIN_ACLKX		(1 << 26)
#define MCASP_PIN_AMUTE		(1 << 25)	// Also, 0 to 3 are XFR0 to XFR3

#ifdef DBOX_CAPE
#define MCASP_OUTPUT_PINS   	MCASP_PIN_AHCLKX | (1 << 2) // AHCLKX and AXR2 outputs
#else
#define MCASP_OUTPUT_PINS   	(1 << 3)	// Which pins are outputs
#endif

#define MCASP_DATA_MASK 	0xFFFF		// 16 bit data
#define MCASP_DATA_FORMAT	0x807C		// MSB first, 0 bit delay, 16 bits, CFG bus, ROR 16bits

#define C_MCASP_MEM             C28     	// Shared PRU mem

// Flags for the flags register
#define FLAG_BIT_BUFFER1	0
#define FLAG_BIT_USE_SPI	1
#define FLAG_BIT_MCASP_HWORD	2		// Whether we are on the high word for McASP transmission
#define FLAG_BIT_USE_DIGITAL 3
// Registers used throughout

// r1, r2, r3 are used for temporary storage
#define MEM_DIGITAL_BASE 0x11000 //Base address for DIGITAL : Shared RAM + 0x400
#define MEM_DIGITAL_BUFFER1_OFFSET 0x400 //Start pointer to DIGITAL_BUFFER1, which is 256 words after.
// 256 is the maximum number of frames allowed

#define r27_current r6  // Pointer to current storage location of DIGITAL
#define reg_num_channels	r9		// Number of SPI ADC/DAC channels to use
#define reg_frame_current	r10		// Current frame count in SPI ADC/DAC transfer
#define reg_frame_total		r11		// Total frame count for SPI ADC/DAC
#define reg_dac_data		r12		// Current dword for SPI DAC
#define reg_adc_data		r13		// Current dword for SPI ADC
#define reg_mcasp_dac_data	r14		// Current dword for McASP DAC
#define reg_mcasp_adc_data	r15		// Current dword for McASP ADC
#define reg_dac_buf0		r16		// Start pointer to SPI DAC buffer 0
#define reg_dac_buf1		r17		// Start pointer to SPI DAC buffer 1
#define reg_dac_current		r18		// Pointer to current storage location of SPI DAC
#define reg_adc_current		r19		// Pointer to current storage location of SPI ADC
#define reg_mcasp_buf0		r20		// Start pointer to McASP DAC buffer 0
#define reg_mcasp_buf1		r21		// Start pointer to McASP DAC buffer 1
#define reg_mcasp_dac_current	r22		// Pointer to current storage location of McASP DAC
#define reg_mcasp_adc_current	r23		// Pointer to current storage location of McASP ADC
#define reg_flags		r24		// Buffer ID (0 and 1) and other flags
#define reg_comm_addr		r25		// Memory address for communicating with ARM
#define reg_spi_addr		r26		// Base address for SPI
// r27, r28 used in macros
#define reg_mcasp_addr		r29		// Base address for McASP

// DIGITAL new code starts here
//0  P8_07 36 0x890/090 66 gpio2[2]
//1  P8_08 37 0x894/094 67 gpio2[3]
//2  P8_09 39 0x89c/09c 69 gpio2[5]
//3  P8_10 38 0x898/098 68 gpio2[4]
//4  P8_11 13 0x834/034 45 gpio1[13]
//5  P8_12 12 0x830/030 44 gpio1[12]
//6  P9_12 30 0x878/078 60 gpio1[28]
//7  P9_14 18 0x848/048 50 gpio1[18]
//8  P8_15 15 0x83c/03c 47 gpio1[15]
//9  P8_16 14 0x838/038 46 gpio1[14]
//10 P9_16 19 0x84c/04c 51 gpio1[19]
//11 P8_18 35 0x88c/08c 65 gpio2[1]
//12 P8_27 56 0x8e0/0e0 86 gpio2[22]
//13 P8_28 58 0x8e8/0e8 88 gpio2[24]
//14 P8_29 57 0x8e4/0e4 87 gpio2[23]
//15 P8_30 59 0x8ec/0ec 89 gpio2[25]

//TODO during initialization, set the pinmuxers to mode 7, input enable
 
//generic GPIOs constants
//#define GPIO1 0x4804c000
#define GPIO2 0x481ac000
//#define GPIO_CLEARDATAOUT 0x190 //SETDATAOUT is CLEARDATAOUT+4
#define GPIO_OE 0x134 
#define GPIO_DATAIN 0x138

//gpioX_cleardataout must be adjacent to gpioX_setdataout
#define reg_gpio1_oe r2
#define reg_gpio2_oe r3
#define reg_gpio2_cleardataout r4
#define reg_gpio2_setdataout r5
#define reg_gpio1_cleardataout r7
#define reg_gpio1_setdataout r8
#define reg_digital r27 //will first contain digitalOut from render() and digitalIn to render() later
//aliases
#define reg_gpio1_datain r2
#define reg_gpio2_datain r3

.macro READ_GPIO_BITS
.mparam gpio_data, gpio_num_bit, digital_bit, digital
    QBBC DONE, digital, digital_bit //if the pin is set as an output, nothing to do here
    QBBC CLEAR, gpio_data, gpio_num_bit 
    SET digital, digital_bit+16
    QBA DONE
    CLEAR:
        CLR digital, digital_bit+16
        QBA DONE
    DONE:
.endm

.macro SET_GPIO_BITS
.mparam gpio_oe, gpio_setdataout, gpio_cleardataout, gpio_num_bit, digital_bit, digital //sets the bits in GPIO_OE, GPIO_SETDATAOUT and GPIO_CLEARDATAOUT
//Remember that the GPIO_OE Output data enable register behaves as follows for each bit:
//0 = The corresponding GPIO pin is configured as an output.
//1 = The corresponding GPIO pin is configured as an input.
    QBBS SETINPUT, digital, digital_bit 
    CLR gpio_oe, gpio_num_bit //if it is an output, configure pin as output
    QBBC CLEARDATAOUT, digital, digital_bit+16 // check the output value. If it is 0, branch
    SET gpio_setdataout, gpio_num_bit //if it is 1, set output to high
    QBA DONE
CLEARDATAOUT:
    SET gpio_cleardataout, gpio_num_bit // set output to low
    QBA DONE
SETINPUT: //if it is an input, set the relevant bit
    SET gpio_oe, gpio_num_bit
    QBA DONE
DONE:
.endm

QBA START // when first starting, go to START, skipping this section.

DIGITAL:
//IMPORTANT: do NOT use r28 in this macro, as it contains the return address for JAL
//r27 is now the input word passed in render(), one word per frame
//[31:16]: data(1=high, 0=low), [15:0]: direction (0=output, 1=input) )


//Preparing the gpio_oe, gpio_cleardataout and gpio_setdataout for each module
//r2 will hold GPIO1_OE
//load current status of GPIO_OE in r2
    MOV r2, GPIO1 | GPIO_OE 
    //it takes 190ns to go through the next instruction
    LBBO r2, r2, 0, 4
//GPIO1-start
//process oe and datain and prepare dataout for GPIO1
//r7 will contain GPIO1_CLEARDATAOUT
//r8 will contain GPIO1_SETDATAOUT
    MOV r8, 0 
    MOV r7, 0
//map GPIO_ANALOG to gpio1 pins,
//r2 is gpio1_oe, r8 is gpio1_setdataout, r7 is gpio1_cleardataout, r27 is the input word
//the following operations will read from r27 and update r2,r7,r8
    SET_GPIO_BITS r2, r8, r7, 13, 4, r27
    SET_GPIO_BITS r2, r8, r7, 12, 5, r27
    SET_GPIO_BITS r2, r8, r7, 28, 6, r27
    SET_GPIO_BITS r2, r8, r7, 18, 7, r27
    SET_GPIO_BITS r2, r8, r7, 15, 8, r27
    SET_GPIO_BITS r2, r8, r7, 14, 9, r27
    SET_GPIO_BITS r2, r8, r7, 19, 10, r27
//set the output enable register for gpio1.
    MOV r3, GPIO1 | GPIO_OE  //use r3 as a temp register
    SBBO r2, r3, 0, 4 //takes two cycles (10ns)
//GPIO1-end
// r2 is now unused

//GPIO2-start
//r3 will hold GPIO1_OE
//load current status of GPIO_OE in r3
    MOV r3, GPIO2 | GPIO_OE  
//it takes 200ns to go through the next instructions
    LBBO r3, r3, 0, 4
//process oe and datain and prepare dataout for GPIO2
//r4 will contain GPIO2_CLEARDATAOUT
//r5 will contain GPIO2_SETDATAOUT
    MOV r5, 0
    MOV r4, 0 
//map GPIO_ANALOG to gpio2 pins
//r3 is gpio2_oe, r5 is gpio2_setdataout, r4 is gpio2_cleardataout, r27 is the input word
//the following operations will read from r27 and update r3,r4,r5
    SET_GPIO_BITS r3, r5, r4, 2, 0, r27
    SET_GPIO_BITS r3, r5, r4, 3, 1, r27
    SET_GPIO_BITS r3, r5, r4, 5, 2, r27
    SET_GPIO_BITS r3, r5, r4, 4, 3, r27
    SET_GPIO_BITS r3, r5, r4, 1, 11, r27
    SET_GPIO_BITS r3, r5, r4, 22, 12, r27
    SET_GPIO_BITS r3, r5, r4, 24, 13, r27
    SET_GPIO_BITS r3, r5, r4, 23, 14, r27
    SET_GPIO_BITS r3, r5, r4, 25, 15, r27
//set the output enable register for gpio2.
    MOV r2, GPIO2 | GPIO_OE  //use r2 as a temp registerp
    SBBO r3, r2, 0, 4 //takes two cycles (10ns)
//GPIO2-end
//r3 is now unused

//load current inputs in r2, r3
//r2 will contain GPIO1_DATAIN
//r3 will contain GPIO2_DATAIN
//load the memory locations
    MOV r2, GPIO1 | GPIO_DATAIN  
    MOV r3, GPIO2 | GPIO_DATAIN  
    //takes 375 nns to go through the next two instructions
//read the datain
    LBBO r2, r2, 0, 4
    LBBO r3, r3, 0, 4
//now read from r2 and r3 only the channels that are set as input in the lower word of r27 
// and set their value in the high word of r27
//GPIO1
    READ_GPIO_BITS r2, 13, 4, r27
    READ_GPIO_BITS r2, 12, 5, r27
    READ_GPIO_BITS r2, 28, 6, r27
    READ_GPIO_BITS r2, 18, 7, r27
    READ_GPIO_BITS r2, 15, 8, r27
    READ_GPIO_BITS r2, 14, 9, r27
    READ_GPIO_BITS r2, 19, 10, r27
//GPIO2
    READ_GPIO_BITS r3, 2, 0, r27
    READ_GPIO_BITS r3, 3, 1, r27
    READ_GPIO_BITS r3, 5, 2, r27
    READ_GPIO_BITS r3, 4, 3, r27
    READ_GPIO_BITS r3, 1, 11, r27
    READ_GPIO_BITS r3, 22, 12, r27
    READ_GPIO_BITS r3, 24, 13, r27
    READ_GPIO_BITS r3, 23, 14, r27
    READ_GPIO_BITS r3, 25, 15, r27
//r2, r3 are now unused

//now all the setdataout and cleardataout are ready to be written to the GPIO register.
//CLEARDATAOUT and SETDATAOUT are consecutive positions in memory, so we just write 8 bytes to CLEARDATAOUT.
//We can do this because we chose cleardata and setdata registers for a given GPIO to be consecutive
//load the memory addresses to be written to
    MOV r2, GPIO1 | GPIO_CLEARDATAOUT //use r2 as a temp register
    MOV r3, GPIO2 | GPIO_CLEARDATAOUT //use r3 as a temp register
//write 8 bytes for each GPIO
//takes 30ns in total to go through the following two instructions
    SBBO r7, r2, 0, 8 //store r7 and r8 in GPIO1_CLEARDATAOUT and GPIO1_SETDATAOUT 
                      //takes 145ns to be effective when going low, 185ns when going high
    SBBO r4, r3, 0, 8 //store r4 and r5 in GPIO2_CLEARDATAOUT and GPIO2_SETDATAOUT 
                     //takes 95ns to be effective when going low, 130ns when going high
//reversing the order of the two lines above will swap the performances between the GPIO modules
//i.e.: the first line will always take 145ns/185ns and the second one will always take 95ns/130ns, 
//regardless of whether the order is gpio1-gpio2 or gpio2-gpio1
JMP r28.w0 // go back to ADC_WRITE_AND_PROCESS_GPIO

.macro HANG //useful for debugging
DALOOP: 
set r30.t14
clr r30.t14
QBA DALOOP
.endm	

// Bring CS line low to write to DAC
.macro DAC_CS_ASSERT
      MOV r27, DAC_CS_PIN
      MOV r28, DAC_GPIO + GPIO_CLEARDATAOUT
      SBBO r27, r28, 0, 4
.endm

// Bring CS line high at end of DAC transaction
.macro DAC_CS_UNASSERT
      MOV r27, DAC_CS_PIN
      MOV r28, DAC_GPIO + GPIO_SETDATAOUT
      SBBO r27, r28, 0, 4
.endm

// Write to DAC TX register
.macro DAC_TX
.mparam data
      SBBO data, reg_spi_addr, SPI_CH0TX, 4
.endm

// Wait for SPI to finish (uses RXS indicator)
.macro DAC_WAIT_FOR_FINISH
 LOOP:
      LBBO r27, reg_spi_addr, SPI_CH0STAT, 4
      QBBC LOOP, r27, 0
.endm

// Read the RX word to clear
.macro DAC_DISCARD_RX
      LBBO r27, reg_spi_addr, SPI_CH0RX, 4
.endm

// Complete DAC write with chip select
.macro DAC_WRITE
.mparam reg
      DAC_CS_ASSERT
      DAC_TX reg
      DAC_WAIT_FOR_FINISH
      DAC_CS_UNASSERT
      DAC_DISCARD_RX
.endm

// Bring CS line low to write to ADC
.macro ADC_CS_ASSERT
      MOV r27, ADC_CS_PIN
      MOV r28, ADC_GPIO + GPIO_CLEARDATAOUT
      SBBO r27, r28, 0, 4
.endm

// Bring CS line high at end of ADC transaction
.macro ADC_CS_UNASSERT
      MOV r27, ADC_CS_PIN
      MOV r28, ADC_GPIO + GPIO_SETDATAOUT
      SBBO r27, r28, 0, 4
.endm

// Write to ADC TX register
.macro ADC_TX
.mparam data
      SBBO data, reg_spi_addr, SPI_CH1TX, 4
.endm

// Wait for SPI to finish (uses RXS indicator)
.macro ADC_WAIT_FOR_FINISH
 LOOP:
      LBBO r27, reg_spi_addr, SPI_CH1STAT, 4
      QBBC LOOP, r27, 0
.endm

// Read the RX word to clear; store output
.macro ADC_RX
.mparam data
      LBBO data, reg_spi_addr, SPI_CH1RX, 4
.endm

// Complete ADC write+read with chip select
.macro ADC_WRITE
.mparam in, out
      ADC_CS_ASSERT
      ADC_TX in
      ADC_WAIT_FOR_FINISH
      ADC_RX out
      ADC_CS_UNASSERT
.endm

// Complete ADC write+read with chip select and also performs IO for digital
.macro ADC_WRITE_GPIO
.mparam in, out, do_gpio
      ADC_CS_ASSERT
      ADC_TX in
      QBBC GPIO_DONE, reg_flags, FLAG_BIT_USE_DIGITAL //skip if DIGITAL is disabled
      AND r27, do_gpio, 0x3 // only do a DIGITAL every 2 SPI I/O
      QBNE GPIO_DONE, r27, 0 
//from here to GPIO_DONE takes 1.8us, while usually ADC_WAIT_FOR_FINISH only waits for 1.14us.
//TODO: it would be better to split the DIGITAL stuff in two parts:
//- one taking place during DAC_WRITE which sets the GPIO_OE
//- and the other during ADC_WRITE which actually reads DATAIN and writes CLEAR/SET DATAOUT
                            //r27 is actually r27, so do not use r27 from here to ...
      LBBO r27, r27_current, 0, 4 
      JAL r28.w0, DIGITAL // note that this is not called as a macro, but with JAL. r28 will contain the return address
      SBBO r27, r27_current, 0,   4 
                            //..here you can start using r27 again
      ADD r27_current, r27_current, 4 //increment pointer
GPIO_DONE:
      ADC_WAIT_FOR_FINISH
      ADC_RX out
      ADC_CS_UNASSERT
.endm

// Write a McASP register
.macro MCASP_REG_WRITE
.mparam reg, value
      MOV r27, value
      SBBO r27, reg_mcasp_addr, reg, 4
.endm

// Write a McASP register beyond the 0xFF boundary
.macro MCASP_REG_WRITE_EXT
.mparam reg, value
      MOV r27, value
      MOV r28, reg
      ADD r28, reg_mcasp_addr, r28
      SBBO r27, r28, 0, 4
.endm

// Read a McASP register
.macro MCASP_REG_READ
.mparam reg, value
      LBBO value, reg_mcasp_addr, reg, 4
.endm
	
// Read a McASP register beyond the 0xFF boundary
.macro MCASP_REG_READ_EXT
.mparam reg, value
      MOV r28, reg
      ADD r28, reg_mcasp_addr, r28
      LBBO value, r28, 0, 4
.endm
	
// Set a bit and wait for it to come up
.macro MCASP_REG_SET_BIT_AND_POLL
.mparam reg, mask
      MOV r27, mask
      LBBO r28, reg_mcasp_addr, reg, 4
      OR r28, r28, r27
      SBBO r28, reg_mcasp_addr, reg, 4
POLL:
      LBBO r28, reg_mcasp_addr, reg, 4
      AND r28, r28, r27
      QBEQ POLL, r28, 0
.endm
   
START:
      // Set up c24 and c25 offsets with CTBIR register
      // Thus C24 points to start of PRU0 RAM
      MOV r3, 0x22020       // CTBIR0
      MOV r2, 0
      SBBO r2, r3, 0, 4

      // Set up c28 pointer offset for shared PRU RAM
      MOV r3, 0x22028       // CTPPR0
      MOV r2, 0x00000120    // To get address 0x00012000
      SBBO r2, r3, 0, 4
	
      // Load useful registers for addressing SPI
      MOV reg_comm_addr, SHARED_COMM_MEM_BASE
      MOV reg_spi_addr, SPI_BASE
      MOV reg_mcasp_addr, MCASP_BASE
	
      // Set ARM such that PRU can write to registers
      LBCO r0, C4, 4, 4
      CLR r0, r0, 4
      SBCO r0, C4, 4, 4

      // Clear flags
      MOV reg_flags, 0

      // Default number of channels in case SPI disabled
      LDI reg_num_channels, 8
	
      // Find out whether we should use DIGITAL
      LBBO r2, reg_comm_addr, COMM_USE_DIGITAL, 4
      QBEQ DIGITAL_INIT_DONE, r2, 0 // if we use digital
      SET reg_flags, reg_flags, FLAG_BIT_USE_DIGITAL 
/* This block of code is not really needed, as the memory is initialized by ARM before the PRU is started.
Will leave it here for future reference
DIGITAL_INIT: //set the digital buffer to 0x0000ffff (all inputs), to prevent unwanted high outputs
              //the loop is unrolled by a factor of four just to take advantage of the speed of SBBO on larger byte bursts, but there is no real need for it
      MOV r2, 0x0000ffff //value to store. 0x0000ffff means all inputs
      MOV r3, MEM_DIGITAL_BASE //start of the digital buffer
      MOV r4, MEM_DIGITAL_BASE+2*MEM_DIGITAL_BUFFER1_OFFSET //end of the digital buffer
DIGITAL_INIT_BUFFER_LOOP:
      SBBO r2, r3, 0, 4 
      ADD r3, r3, 4 //increment pointer
      QBGT DIGITAL_INIT_BUFFER_LOOP, r3, r4 //loop until we reach the end of the buffer
*/
DIGITAL_INIT_DONE:
      // Find out whether we should use SPI ADC and DAC
      LBBO r2, reg_comm_addr, COMM_USE_SPI, 4
      QBEQ SPI_FLAG_CHECK_DONE, r2, 0
      SET reg_flags, reg_flags, FLAG_BIT_USE_SPI
SPI_FLAG_CHECK_DONE:
      // If we don't use SPI, then skip all this init
      QBBC SPI_INIT_DONE, reg_flags, FLAG_BIT_USE_SPI

      // Load the number of channels: valid values are 8, 4 or 2
      LBBO reg_num_channels, reg_comm_addr, COMM_NUM_CHANNELS, 4
      QBGT SPI_NUM_CHANNELS_LT8, reg_num_channels, 8 // 8 > num_channels ?
      LDI reg_num_channels, 8		// If N >= 8, N = 8
      QBA SPI_NUM_CHANNELS_DONE
SPI_NUM_CHANNELS_LT8:	
      QBGT SPI_NUM_CHANNELS_LT4, reg_num_channels, 4 // 4 > num_channels ?
      LDI reg_num_channels, 4		// If N >= 4, N = 4
      QBA SPI_NUM_CHANNELS_DONE
SPI_NUM_CHANNELS_LT4:
      LDI reg_num_channels, 2		// else N = 2
SPI_NUM_CHANNELS_DONE:	
	
      // Init SPI clock
      MOV r2, 0x02
      MOV r3, CLOCK_BASE + CLOCK_SPI0
      SBBO r2, r3, 0, 4

      // Reset SPI and wait for finish
      MOV r2, 0x02
      SBBO r2, reg_spi_addr, SPI_SYSCONFIG, 4

SPI_WAIT_RESET:
      LBBO r2, reg_spi_addr, SPI_SYSSTATUS, 4
      QBBC SPI_WAIT_RESET, r2, 0
	
      // Turn off SPI channels
      MOV r2, 0
      SBBO r2, reg_spi_addr, SPI_CH0CTRL, 4
      SBBO r2, reg_spi_addr, SPI_CH1CTRL, 4
  
      // Set to master; chip select lines enabled (CS0 used for DAC)
      MOV r2, 0x00
      SBBO r2, reg_spi_addr, SPI_MODULCTRL, 4
  
      // Configure CH0 for DAC
      MOV r2, (3 << 27) | (DAC_DPE << 16) | (DAC_TRM << 12) | ((DAC_WL - 1) << 7) | (DAC_CLK_DIV << 2) | DAC_CLK_MODE | (1 << 6)
      SBBO r2, reg_spi_addr, SPI_CH0CONF, 4

      // Configure CH1 for ADC
      MOV r2, (3 << 27) | (ADC_DPE << 16) | (ADC_TRM << 12) | ((ADC_WL - 1) << 7) | (ADC_CLK_DIV << 2) | ADC_CLK_MODE
      SBBO r2, reg_spi_addr, SPI_CH1CONF, 4
   
      // Turn on SPI channels
      MOV r2, 0x01
      SBBO r2, reg_spi_addr, SPI_CH0CTRL, 4
      SBBO r2, reg_spi_addr, SPI_CH1CTRL, 4   

      // DAC power-on reset sequence
      MOV r2, (0x07 << AD5668_COMMAND_OFFSET)
      DAC_WRITE r2

      // Initialise ADC
      MOV r2, AD7699_CFG_MASK | (0 << AD7699_CHANNEL_OFFSET) | (0 << AD7699_SEQ_OFFSET)
      ADC_WRITE r2, r2

      // Enable DAC internal reference
      MOV r2, (0x08 << AD5668_COMMAND_OFFSET) | (0x01 << AD5668_REF_OFFSET)
      DAC_WRITE r2
	
      // Read ADC ch0 and ch1: result is always 2 samples behind so start here
      MOV r2, AD7699_CFG_MASK | (0x00 << AD7699_CHANNEL_OFFSET)
      ADC_WRITE r2, r2

      MOV r2, AD7699_CFG_MASK | (0x01 << AD7699_CHANNEL_OFFSET)
      ADC_WRITE r2, r2
SPI_INIT_DONE:	
	
// Prepare McASP0 for audio
MCASP_REG_WRITE MCASP_GBLCTL, 0			// Disable McASP
MCASP_REG_WRITE_EXT MCASP_SRCTL0, 0		// All serialisers off
MCASP_REG_WRITE_EXT MCASP_SRCTL1, 0
MCASP_REG_WRITE_EXT MCASP_SRCTL2, 0
MCASP_REG_WRITE_EXT MCASP_SRCTL3, 0
MCASP_REG_WRITE_EXT MCASP_SRCTL4, 0
MCASP_REG_WRITE_EXT MCASP_SRCTL5, 0

MCASP_REG_WRITE MCASP_PWRIDLESYSCONFIG, 0x02	// Power on
MCASP_REG_WRITE MCASP_PFUNC, 0x00		// All pins are McASP
MCASP_REG_WRITE MCASP_PDIR, MCASP_OUTPUT_PINS	// Set pin direction
MCASP_REG_WRITE MCASP_DLBCTL, 0x00
MCASP_REG_WRITE MCASP_DITCTL, 0x00
MCASP_REG_WRITE MCASP_RMASK, MCASP_DATA_MASK	// 16 bit data receive
MCASP_REG_WRITE MCASP_RFMT, MCASP_DATA_FORMAT	// Set data format
MCASP_REG_WRITE MCASP_AFSRCTL, 0x100		// I2S mode
MCASP_REG_WRITE MCASP_ACLKRCTL, 0x80		// Sample on rising edge
MCASP_REG_WRITE MCASP_AHCLKRCTL, 0x8001		// Internal clock, not inv, /2; irrelevant?
MCASP_REG_WRITE MCASP_RTDM, 0x03		// Enable TDM slots 0 and 1
MCASP_REG_WRITE MCASP_RINTCTL, 0x00		// No interrupts
MCASP_REG_WRITE MCASP_XMASK, MCASP_DATA_MASK	// 16 bit data transmit
MCASP_REG_WRITE MCASP_XFMT, MCASP_DATA_FORMAT	// Set data format
MCASP_REG_WRITE MCASP_AFSXCTL, 0x100		// I2S mode
MCASP_REG_WRITE MCASP_ACLKXCTL, 0x00		// Transmit on rising edge, sync. xmit and recv
MCASP_REG_WRITE MCASP_AHCLKXCTL, 0x8001		// External clock from AHCLKX
MCASP_REG_WRITE MCASP_XTDM, 0x03		// Enable TDM slots 0 and 1
MCASP_REG_WRITE MCASP_XINTCTL, 0x00		// No interrupts
	
MCASP_REG_WRITE_EXT MCASP_SRCTL_R, 0x02		// Set up receive serialiser
MCASP_REG_WRITE_EXT MCASP_SRCTL_X, 0x01		// Set up transmit serialiser
MCASP_REG_WRITE_EXT MCASP_WFIFOCTL, 0x00	// Disable FIFOs
MCASP_REG_WRITE_EXT MCASP_RFIFOCTL, 0x00

MCASP_REG_WRITE MCASP_XSTAT, 0xFF		// Clear transmit errors
MCASP_REG_WRITE MCASP_RSTAT, 0xFF		// Clear receive errors

MCASP_REG_SET_BIT_AND_POLL MCASP_RGBLCTL, (1 << 1)	// Set RHCLKRST
MCASP_REG_SET_BIT_AND_POLL MCASP_XGBLCTL, (1 << 9)	// Set XHCLKRST

// The above write sequence will have temporarily changed the AHCLKX frequency
// The PLL needs time to settle or the sample rate will be unstable and possibly
// cause an underrun. Give it ~1ms before going on.
// 10ns per loop iteration = 10^-8s --> 10^5 iterations needed

      MOV r2, 1 << 28
      MOV r3, GPIO1 + GPIO_SETDATAOUT
      SBBO r2, r3, 0, 4

MOV r2, 100000
MCASP_INIT_WAIT:	
      SUB r2, r2, 1
      QBNE MCASP_INIT_WAIT, r2, 0

      MOV r2, 1 << 28
      MOV r3, GPIO1 + GPIO_CLEARDATAOUT
      SBBO r2, r3, 0, 4
	
MCASP_REG_SET_BIT_AND_POLL MCASP_RGBLCTL, (1 << 0)	// Set RCLKRST
MCASP_REG_SET_BIT_AND_POLL MCASP_XGBLCTL, (1 << 8)	// Set XCLKRST
MCASP_REG_SET_BIT_AND_POLL MCASP_RGBLCTL, (1 << 2)	// Set RSRCLR
MCASP_REG_SET_BIT_AND_POLL MCASP_XGBLCTL, (1 << 10)	// Set XSRCLR
MCASP_REG_SET_BIT_AND_POLL MCASP_RGBLCTL, (1 << 3)	// Set RSMRST
MCASP_REG_SET_BIT_AND_POLL MCASP_XGBLCTL, (1 << 11)	// Set XSMRST

MCASP_REG_WRITE_EXT MCASP_XBUF, 0x00		// Write to the transmit buffer to prevent underflow

MCASP_REG_SET_BIT_AND_POLL MCASP_RGBLCTL, (1 << 4)	// Set RFRST
MCASP_REG_SET_BIT_AND_POLL MCASP_XGBLCTL, (1 << 12)	// Set XFRST

// Initialisation
    LBBO reg_frame_total, reg_comm_addr, COMM_BUFFER_FRAMES, 4  // Total frame count (SPI; 0.5x-2x for McASP)
    MOV reg_dac_buf0, 0                      // DAC buffer 0 start pointer
    LSL reg_dac_buf1, reg_frame_total, 1     // DAC buffer 1 start pointer = N[ch]*2[bytes]*bufsize
    LMBD r2, reg_num_channels, 1		 // Returns 1, 2 or 3 depending on the number of channels
    LSL reg_dac_buf1, reg_dac_buf1, r2	 // Multiply by 2, 4 or 8 to get the N[ch] scaling above
    MOV reg_mcasp_buf0, 0			 // McASP DAC buffer 0 start pointer
    LSL reg_mcasp_buf1, reg_frame_total, r2  // McASP DAC buffer 1 start pointer = 2[ch]*2[bytes]*(N/4)[samples/spi]*bufsize
    CLR reg_flags, reg_flags, FLAG_BIT_BUFFER1  // Bit 0 holds which buffer we are on
    MOV r2, 0
    SBBO r2, reg_comm_addr, COMM_FRAME_COUNT, 4  // Start with frame count of 0
/* This block of code is not really needed, as the memory is initialized by ARM before the PRU is started.
Will leave it here for future reference
//Initialise all SPI and audio buffers (DAC0, DAC1, ADC0, ADC1) to zero.
//This is useful for analog outs so they do not have spikes during the first buffer.
//This is not very useful for audio, as you still hear the initial "tumpf" when the converter starts 
//and each sample in the DAC buffer is reset to 0 after it is written to the DAC.

    QBBC SPI_INIT_BUFFER_DONE, reg_flags, FLAG_BIT_USE_SPI
//Initialize SPI buffers
//compute the memory offset of the end of the audio buffer and store it in r4
    SUB r4, reg_dac_buf1, reg_dac_buf0 // length of the buffer, assumes reg_dac_buf1>ref_dac_buf0
    LSL r4, r4, 2 //length of four buffers (DAC0, DAC1, ADC0, ADC1)
    ADD r4, reg_dac_buf0, r4 //total offset
    MOV r2, 0// value to store
    MOV r3, 0 // offset counter
SPI_INIT_BUFFER_LOOP:
    SBCO r2, C_ADC_DAC_MEM, r3, 4
    ADD r3, r3, 4
    QBGT SPI_INIT_BUFFER_LOOP, r3, r4
SPI_INIT_BUFFER_DONE:

//Initialize audio buffers
//compute the memory offset of the end of the audio buffer and store it in r4
    SUB r4, reg_mcasp_buf1, reg_mcasp_buf0 // length of the buffer, assumes reg_mcasp_buf1>ref_mcasp_buf0
    LSL r4, r4, 2 //length of four buffers (DAC0, DAC1, ADC0, ADC1)
    ADD r4, reg_mcasp_buf0, r4 //total offset
    MOV r2, 0 // value to store
    MOV r3, 0 // offset counter
    MCASP_INIT_BUFFER_LOOP:
    SBCO r2, C_MCASP_MEM, r3, 4
    ADD r3, r3, 4
    QBGT MCASP_INIT_BUFFER_LOOP, r3, r4
*/
// Here we are out of sync by one TDM slot since the 0 word transmitted above will have occupied
// the first output slot. Send one more word before jumping into the loop.
MCASP_DAC_WAIT_BEFORE_LOOP:	
      LBBO r2, reg_mcasp_addr, MCASP_XSTAT, 4
      QBBC MCASP_DAC_WAIT_BEFORE_LOOP, r2, MCASP_XSTAT_XDATA_BIT

      MCASP_REG_WRITE_EXT MCASP_XBUF, 0x00

// Likewise, read and discard the first sample we get back from the ADC. This keeps the DAC and ADC
// in sync in terms of which TDM slot we are reading (empirically found that we should throw this away
// rather than keep it and invert the phase)
MCASP_ADC_WAIT_BEFORE_LOOP:
      LBBO r2, reg_mcasp_addr, MCASP_RSTAT, 4
      QBBC MCASP_ADC_WAIT_BEFORE_LOOP, r2, MCASP_RSTAT_RDATA_BIT

      MCASP_REG_READ_EXT MCASP_RBUF, r2
	
WRITE_ONE_BUFFER:

      // Write a single buffer of DAC samples and read a buffer of ADC samples
      // Load starting positions
      MOV reg_dac_current, reg_dac_buf0         // DAC: reg_dac_current is current pointer
      LMBD r2, reg_num_channels, 1		// 1, 2 or 3 for 2, 4 or 8 channels
      LSL reg_adc_current, reg_frame_total, r2
      LSL reg_adc_current, reg_adc_current, 2   // N * 2 * 2 * bufsize
      ADD reg_adc_current, reg_adc_current, reg_dac_current // ADC: starts N * 2 * 2 * bufsize beyond DAC
      MOV reg_mcasp_dac_current, reg_mcasp_buf0 // McASP: set current DAC pointer
      LSL reg_mcasp_adc_current, reg_frame_total, r2 // McASP ADC: starts (N/2)*2*2*bufsize beyond DAC
      LSL reg_mcasp_adc_current, reg_mcasp_adc_current, 1
      ADC reg_mcasp_adc_current, reg_mcasp_adc_current, reg_mcasp_dac_current
      MOV reg_frame_current, 0
      QBBS DIGITAL_BASE_CHECK_SET, reg_flags, FLAG_BIT_BUFFER1  //check which buffer we are using for DIGITAL
                  // if we are here, we are using buffer0 
      MOV r27_current, MEM_DIGITAL_BASE
      QBA DIGITAL_BASE_CHECK_DONE
DIGITAL_BASE_CHECK_SET: //if we are here, we are using buffer1 
      MOV r27_current, MEM_DIGITAL_BASE+MEM_DIGITAL_BUFFER1_OFFSET //so adjust offset appropriately
DIGITAL_BASE_CHECK_DONE:

WRITE_LOOP:
      // Write N channels to DAC from successive values in memory
      // At the same time, read N channels from ADC
      // Unrolled by a factor of 2 to get high and low words
      MOV r1, 0
ADC_DAC_LOOP:
      QBBC SPI_DAC_LOAD_DONE, reg_flags, FLAG_BIT_USE_SPI
      // Load next 2 SPI DAC samples and store zero in their place
      LBCO reg_dac_data, C_ADC_DAC_MEM, reg_dac_current, 4
      MOV r2, 0
      SBCO r2, C_ADC_DAC_MEM, reg_dac_current, 4
      ADD reg_dac_current, reg_dac_current, 4
SPI_DAC_LOAD_DONE:

      // On even iterations, load two more samples and choose the first one
      // On odd iterations, transmit the second of the samples already loaded
      // QBBS MCASP_DAC_HIGH_WORD, r1, 1
      QBBS MCASP_DAC_HIGH_WORD, reg_flags, FLAG_BIT_MCASP_HWORD
MCASP_DAC_LOW_WORD:	
      // Load next 2 Audio DAC samples and store zero in their place
      LBCO reg_mcasp_dac_data, C_MCASP_MEM, reg_mcasp_dac_current, 4
      MOV r2, 0
      SBCO r2, C_MCASP_MEM, reg_mcasp_dac_current, 4
      ADD reg_mcasp_dac_current, reg_mcasp_dac_current, 4

      // Mask out the low word (first in little endian)
      MOV r2, 0xFFFF
      AND r7, reg_mcasp_dac_data, r2
	
      QBA MCASP_WAIT_XSTAT
MCASP_DAC_HIGH_WORD:
      // Take the high word of the previously loaded data
      LSR r7, reg_mcasp_dac_data, 16
	
      // Every 2 channels we send one audio sample; this loop already
      // sends exactly two SPI channels.
      // Wait for McASP XSTAT[XDATA] to set indicating we can write more data
MCASP_WAIT_XSTAT:
      LBBO r2, reg_mcasp_addr, MCASP_XSTAT, 4
      QBBC MCASP_WAIT_XSTAT, r2, MCASP_XSTAT_XDATA_BIT

      MCASP_REG_WRITE_EXT MCASP_XBUF, r7
	
      // Same idea with ADC: even iterations, load the sample into the low word, odd
      // iterations, load the sample into the high word and store
      // QBBS MCASP_ADC_HIGH_WORD, r1, 1
      QBBS MCASP_ADC_HIGH_WORD, reg_flags, FLAG_BIT_MCASP_HWORD
MCASP_ADC_LOW_WORD:	
      // Start ADC data at 0
      LDI reg_mcasp_adc_data, 0
	
      // Now wait for a received word to become available from the audio ADC
MCASP_WAIT_RSTAT_LOW:
      LBBO r2, reg_mcasp_addr, MCASP_RSTAT, 4
      QBBC MCASP_WAIT_RSTAT_LOW, r2, MCASP_RSTAT_RDATA_BIT

      // Mask low word and store in ADC data register
      MCASP_REG_READ_EXT MCASP_RBUF, r3
      MOV r2, 0xFFFF
      AND reg_mcasp_adc_data, r3, r2
      QBA MCASP_ADC_DONE

MCASP_ADC_HIGH_WORD:	
      // Wait for a received word to become available from the audio ADC
MCASP_WAIT_RSTAT_HIGH:
      LBBO r2, reg_mcasp_addr, MCASP_RSTAT, 4
      QBBC MCASP_WAIT_RSTAT_HIGH, r2, MCASP_RSTAT_RDATA_BIT

      // Read data and shift 16 bits to the left (into the high word)
      MCASP_REG_READ_EXT MCASP_RBUF, r3
      LSL r3, r3, 16
      OR reg_mcasp_adc_data, reg_mcasp_adc_data, r3

      // Now store the result and increment the pointer
      SBCO reg_mcasp_adc_data, C_MCASP_MEM, reg_mcasp_adc_current, 4
      ADD reg_mcasp_adc_current, reg_mcasp_adc_current, 4
MCASP_ADC_DONE:	
      QBBC SPI_SKIP_WRITE, reg_flags, FLAG_BIT_USE_SPI

      // DAC: transmit low word (first in little endian)
      MOV r2, 0xFFFF
      AND r7, reg_dac_data, r2
      LSL r7, r7, AD5668_DATA_OFFSET
      MOV r8, (0x03 << AD5668_COMMAND_OFFSET)
      OR r7, r7, r8
      LSL r8, r1, AD5668_ADDRESS_OFFSET
      OR r7, r7, r8
      DAC_WRITE r7

      // Read ADC channels: result is always 2 commands behind
      // Start by reading channel 2 (result is channel 0) and go
      // to N+2, but masking the channel number to be between 0 and N-1
      LDI reg_adc_data, 0
      ADD r8, r1, 2
      SUB r7, reg_num_channels, 1
      AND r8, r8, r7
      LSL r8, r8, AD7699_CHANNEL_OFFSET
      MOV r7, AD7699_CFG_MASK
      OR r7, r7, r8

//ssssssssssssssssssssssssssss
      ADC_WRITE_GPIO r7, r7, r1

      // Mask out only the relevant 16 bits and store in reg_adc_data
      MOV r2, 0xFFFF
      AND reg_adc_data, r7, r2

      // Increment channel index
      ADD r1, r1, 1

      // DAC: transmit high word (second in little endian)
      LSR r7, reg_dac_data, 16
      LSL r7, r7, AD5668_DATA_OFFSET
      MOV r8, (0x03 << AD5668_COMMAND_OFFSET)
      OR r7, r7, r8
      LSL r8, r1, AD5668_ADDRESS_OFFSET
      OR r7, r7, r8
      DAC_WRITE r7

      // Read ADC channels: result is always 2 commands behind
      // Start by reading channel 2 (result is channel 0) and go
      // to N+2, but masking the channel number to be between 0 and N-1
      ADD r8, r1, 2
      SUB r7, reg_num_channels, 1
      AND r8, r8, r7
      LSL r8, r8, AD7699_CHANNEL_OFFSET
      MOV r7, AD7699_CFG_MASK
      OR r7, r7, r8
      ADC_WRITE r7, r7

      // Move this result up to the 16 high bits
      LSL r7, r7, 16
      OR reg_adc_data, reg_adc_data, r7

      // Store 2 ADC words in memory
      SBCO reg_adc_data, C_ADC_DAC_MEM, reg_adc_current, 4
      ADD reg_adc_current, reg_adc_current, 4

      // Toggle the high/low word for McASP control (since we send one word out of
      // 32 bits for each pair of SPI channels)
      XOR reg_flags, reg_flags, (1 << FLAG_BIT_MCASP_HWORD)
	
      // Repeat 4 times for 8 channels (2 samples per loop, r1 += 1 already happened)
      // For 4 or 2 channels, repeat 2 or 1 times, according to flags
      ADD r1, r1, 1
      QBNE ADC_DAC_LOOP, r1, reg_num_channels
      QBA ADC_DAC_LOOP_DONE
SPI_SKIP_WRITE:
      // We get here only if the SPI ADC and DAC are disabled
      // Just keep the loop going for McASP

      // Toggle the high/low word for McASP control (since we send one word out of
      // 32 bits for each pair of SPI channels)
      XOR reg_flags, reg_flags, (1 << FLAG_BIT_MCASP_HWORD)

      ADD r1, r1, 2
      QBNE ADC_DAC_LOOP, r1, reg_num_channels
	
ADC_DAC_LOOP_DONE:	
      // Increment number of frames, see if we have more to write
      ADD reg_frame_current, reg_frame_current, 1
      QBNE WRITE_LOOP, reg_frame_current, reg_frame_total

WRITE_LOOP_DONE:
      // Now done, swap the buffers and do the next one
      // Use r2 as a temp register
      MOV r2, reg_dac_buf0
      MOV reg_dac_buf0, reg_dac_buf1
      MOV reg_dac_buf1, r2
      MOV r2, reg_mcasp_buf0
      MOV reg_mcasp_buf0, reg_mcasp_buf1
      MOV reg_mcasp_buf1, r2
      XOR reg_flags, reg_flags, (1 << FLAG_BIT_BUFFER1) //flip the buffer flag

      // Notify ARM of buffer swap
      AND r2, reg_flags, (1 << FLAG_BIT_BUFFER1)    // Mask out every but low bit
      SBBO r2, reg_comm_addr, COMM_CURRENT_BUFFER, 4

      // Increment the frame count in the comm buffer (for status monitoring)
      LBBO r2, reg_comm_addr, COMM_FRAME_COUNT, 4
      ADD r2, r2, reg_frame_total
      SBBO r2, reg_comm_addr, COMM_FRAME_COUNT, 4

      // If LED blink enabled, toggle every 4096 frames
      LBBO r3, reg_comm_addr, COMM_LED_ADDRESS, 4
      QBEQ LED_BLINK_DONE, r3, 0	
      MOV r1, 0x1000
      AND r2, r2, r1          // Test (frame count & 4096)
      QBEQ LED_BLINK_OFF, r2, 0
      LBBO r2, reg_comm_addr, COMM_LED_PIN_MASK, 4	
      MOV r1, GPIO_SETDATAOUT
      ADD r3, r3, r1          // Address for GPIO set register
      SBBO r2, r3, 0, 4       // Set GPIO pin
      QBA LED_BLINK_DONE
LED_BLINK_OFF:
      LBBO r2, reg_comm_addr, COMM_LED_PIN_MASK, 4
      MOV r1, GPIO_CLEARDATAOUT
      ADD r3, r3, r1          // Address for GPIO clear register
      SBBO r2, r3, 0, 4       // Clear GPIO pin	
LED_BLINK_DONE:	
      // Check if we should finish: flag is zero as long as it should run
      LBBO r2, reg_comm_addr, COMM_SHOULD_STOP, 4
      QBEQ WRITE_ONE_BUFFER, r2, 0

CLEANUP:
      MCASP_REG_WRITE MCASP_GBLCTL, 0x00	// Turn off McASP

      // Turn off SPI if enabled
      QBBC SPI_CLEANUP_DONE, reg_flags, FLAG_BIT_USE_SPI
	
      MOV r3, SPI_BASE + SPI_CH0CONF
      LBBO r2, r3, 0, 4
      CLR r2, r2, 13
      CLR r2, r2, 27
      SBBO r2, r3, 0, 4

      MOV r3, SPI_BASE + SPI_CH0CTRL
      LBBO r2, r3, 0, 4
      CLR r2, r2, 1
      SBBO r2, r3, 0, 4      
SPI_CLEANUP_DONE:
      // Signal the ARM that we have finished 
      MOV R31.b0, PRU0_ARM_INTERRUPT + 16
      HALT