/**

  * $Id$

  * SCIF (Serial Communication Interface with FIFO) implementation - part of the 

  * SH4 standard on-chip peripheral set. The SCIF is hooked up to the DCs

  * external serial port

  *

  * Copyright (c) 2005 Nathan Keynes.

  *

  * This program is free software; you can redistribute it and/or modify

  * it under the terms of the GNU General Public License as published by

  * the Free Software Foundation; either version 2 of the License, or

  * (at your option) any later version.

  *

  * This program is distributed in the hope that it will be useful,

  * but WITHOUT ANY WARRANTY; without even the implied warranty of

  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

  * GNU General Public License for more details.

  */

 #include <glib.h>

 #include "dream.h"

 #include "mem.h"

 #include "sh4/sh4core.h"

 #include "sh4/sh4mmio.h"

 #include "sh4/intc.h"

 #include "sh4/dmac.h"

 #include "clock.h"

 #include "serial.h"

 void SCIF_set_break(void);

 /************************* External serial interface ************************/

 /**

  * Note: serial_* operations are called from outside the SH4, and as such are

  * named relative to the external serial device. SCIF_* operations are only

  * called internally to the SH4 and so are named relative to the CPU.

  */

 /**

  * Storage space for inbound/outbound data blocks. It's a little more

  * convenient for serial consumers to be able to deal with block-sized pieces

  * rather than a byte at a time, even if it makes all this look rather

  * complicated.

  *

  * Currently there's no limit on the number of blocks that can be queued up.

  */

 typedef struct serial_data_block {

     uint32_t length;

     uint32_t offset;

     struct serial_data_block *next;

     char data[];

 } *serial_data_block_t;

 serial_data_block_t serial_recvq_head = NULL, serial_recvq_tail = NULL;

 serial_device_t serial_device = NULL;

 void serial_attach_device( serial_device_t dev ) 

 {

     if( serial_device != NULL )

 	serial_detach_device();

     serial_device = dev;

 }

 void serial_detach_device( void )

 {

     serial_device = NULL;

 }

 /**

  * Add a block of data to the serial receive queue. The data will be received

  * by the CPU at the appropriate baud rate.

  */

 void serial_transmit_data( char *data, int length ) {

     if( length == 0 )

 	return;

     serial_data_block_t block = 

 	g_malloc( sizeof( struct serial_data_block ) + length );

     block->length = length;

     block->offset = 0;

     block->next = NULL;

     memcpy( block->data, data, length );

     if( serial_recvq_head == NULL ) {

 	serial_recvq_head = serial_recvq_tail = block;

     } else {

 	serial_recvq_tail->next = block;

 	serial_recvq_tail = block;

     }

 }

 /**

  * Dequeue a byte from the serial input queue

  */

 static int serial_transmit_dequeue( ) {

     if( serial_recvq_head != NULL ) {

 	uint8_t val = serial_recvq_head->data[serial_recvq_head->offset++];

 	if( serial_recvq_head->offset >= serial_recvq_head->length ) {

 	    serial_data_block_t next = serial_recvq_head->next;

 	    g_free( serial_recvq_head );

 	    serial_recvq_head = next;

 	    if( next == NULL )

 		serial_recvq_tail = NULL;

 	}

 	return (int)(unsigned int)val;

     }

     return -1;

 }

 void serial_transmit_break() {

     SCIF_set_break();

 }

 /********************************* SCIF *************************************/

 #define FIFO_LENGTH 16

 #define FIFO_ARR_LENGTH (FIFO_LENGTH+1)

 /* Serial control register flags */

 #define SCSCR2_TIE  0x80

 #define SCSCR2_RIE  0x40

 #define SCSCR2_TE   0x20

 #define SCSCR2_RE   0x10

 #define SCSCR2_REIE 0x08

 #define SCSCR2_CKE 0x02

 #define IS_TRANSMIT_IRQ_ENABLED() (MMIO_READ(SCIF,SCSCR2) & SCSCR2_TIE)

 #define IS_RECEIVE_IRQ_ENABLED() (MMIO_READ(SCIF,SCSCR2) & SCSCR2_RIE)

 #define IS_RECEIVE_ERROR_IRQ_ENABLED() (MMIO_READ(SCIF,SCSCR2) & (SCSCR2_RIE|SCSCR2_REIE))

 /* Receive is enabled if the RE bit is set in SCSCR2, and the ORER bit is cleared in SCLSR2 */

 #define IS_RECEIVE_ENABLED() ( (MMIO_READ(SCIF,SCSCR2) & SCSCR2_RE) && ((MMIO_READ(SCIF,SCLSR2) & SCLSR2_ORER) == 0) )

 /* Transmit is enabled if the TE bit is set in SCSCR2 */

 #define IS_TRANSMIT_ENABLED() (MMIO_READ(SCIF,SCSCR2) & SCSCR2_TE)

 #define IS_LOOPBACK_ENABLED() (MMIO_READ(SCIF,SCFCR2) & SCFCR2_LOOP)

 /* Serial status register flags */

 #define SCFSR2_ER   0x80

 #define SCFSR2_TEND 0x40

 #define SCFSR2_TDFE 0x20

 #define SCFSR2_BRK  0x10

 #define SCFSR2_RDF  0x02

 #define SCFSR2_DR   0x01

 /* FIFO control register flags */

 #define SCFCR2_MCE   0x08

 #define SCFCR2_TFRST 0x04

 #define SCFCR2_RFRST 0x02

 #define SCFCR2_LOOP  0x01

 /* Line Status Register */

 #define SCLSR2_ORER 0x01

 struct SCIF_fifo {

     int head;

     int tail;

     int trigger;

     uint8_t data[FIFO_ARR_LENGTH];

 };

 int SCIF_recvq_triggers[4] = {1, 4, 8, 14};

 struct SCIF_fifo SCIF_recvq = {0,0,1};

 int SCIF_sendq_triggers[4] = {8, 4, 2, 1};

 struct SCIF_fifo SCIF_sendq = {0,0,8};

 /**

  * Flag to indicate if data was received (ie added to the receive queue)

  * during the last SCIF clock tick. Used to determine when to set the DR

  * flag.

  */

 gboolean SCIF_rcvd_last_tick = FALSE;

 uint32_t SCIF_tick_period = 0;

 uint32_t SCIF_tick_remainder = 0;

 void SCIF_save_state( FILE *f ) 

 {

     fwrite( &SCIF_recvq, sizeof(SCIF_recvq), 1, f );

     fwrite( &SCIF_sendq, sizeof(SCIF_sendq), 1, f );

     fwrite( &SCIF_rcvd_last_tick, sizeof(gboolean), 1, f );

 }

 int SCIF_load_state( FILE *f ) 

 {

     fread( &SCIF_recvq, sizeof(SCIF_recvq), 1, f );

     fread( &SCIF_sendq, sizeof(SCIF_sendq), 1, f );

     fread( &SCIF_rcvd_last_tick, sizeof(gboolean), 1, f );

     return 0;

 }

 static inline uint8_t SCIF_recvq_size( ) 

 {

     int val = SCIF_recvq.tail - SCIF_recvq.head;

     if( val < 0 ) {

 	val = FIFO_ARR_LENGTH - SCIF_recvq.head + SCIF_recvq.tail;

     }

     return val;

 }

 int SCIF_recvq_dequeue( gboolean clearFlags )

 {

     uint8_t result;

     uint32_t tmp, length;

     if( SCIF_recvq.head == SCIF_recvq.tail )

 	return -1; /* No data */

     result = SCIF_recvq.data[SCIF_recvq.head++];

     if( SCIF_recvq.head > FIFO_LENGTH )

 	SCIF_recvq.head = 0;

     /* Update data count register */

     tmp = MMIO_READ( SCIF, SCFDR2 ) & 0xF0;

     length = SCIF_recvq_size();

     MMIO_WRITE( SCIF, SCFDR2, tmp | length );

     /* Clear flags (if requested ) */

     if( clearFlags && length < SCIF_recvq.trigger ) {

 	tmp = SCFSR2_RDF;

 	if( length == 0 )

 	    tmp |= SCFSR2_DR;

 	tmp = MMIO_READ( SCIF, SCFSR2 ) & (~tmp);

 	MMIO_WRITE( SCIF, SCFSR2, tmp );

 	/* If both flags are cleared, clear the interrupt as well */

 	if( (tmp & (SCFSR2_DR|SCFSR2_RDF)) == 0 && IS_RECEIVE_IRQ_ENABLED() )

 	    intc_clear_interrupt( INT_SCIF_RXI );

     }

     return (int)(unsigned int)result;

 }

 gboolean SCIF_recvq_enqueue( uint8_t value )

 {

     uint32_t tmp, length;

     int newpos = SCIF_recvq.tail + 1;

     if( newpos > FIFO_LENGTH )

 	newpos = 0;

     if( newpos == SCIF_recvq.head ) {

 	/* FIFO full - set ORER and discard the value */

 	MMIO_WRITE( SCIF, SCLSR2, SCLSR2_ORER );

 	if( IS_RECEIVE_ERROR_IRQ_ENABLED() )

 	    intc_raise_interrupt( INT_SCIF_ERI );

 	return FALSE;

     }

     SCIF_recvq.data[SCIF_recvq.tail] = value;

     /* Update data count register */

     tmp = MMIO_READ( SCIF, SCFDR2 ) & 0xF0;

     length = SCIF_recvq_size();

     MMIO_WRITE( SCIF, SCFDR2, tmp | length );

     /* Update status register */

     tmp = MMIO_READ( SCIF, SCFSR2 );

     if( length >= SCIF_recvq.trigger ) {

 	tmp |= SCFSR2_RDF;

 	if( IS_RECEIVE_IRQ_ENABLED() ) 

 	    intc_raise_interrupt( INT_SCIF_RXI );

         DMAC_trigger( DMAC_SCIF_RDF );

     }

     MMIO_WRITE( SCIF, SCFSR2, tmp );

     return TRUE;

 }

 /**

  * Reset the receive FIFO to its initial state. Manual is unclear as to

  * whether this also clears flags/interrupts, but we're assuming here that

  * it does until proven otherwise.

  */

 void SCIF_recvq_clear( void ) 

 {

     SCIF_recvq.head = SCIF_recvq.tail = 0;

     MMIO_WRITE( SCIF, SCFDR2, MMIO_READ( SCIF, SCFDR2 ) & 0xF0 );

     MMIO_WRITE( SCIF, SCFSR2, MMIO_READ( SCIF, SCFSR2 ) & ~(SCFSR2_DR|SCFSR2_RDF) );

     if( IS_RECEIVE_IRQ_ENABLED() )

 	intc_clear_interrupt( INT_SCIF_RXI );

 }

 static inline uint8_t SCIF_sendq_size( ) 

 {

     int val = SCIF_sendq.tail - SCIF_sendq.head;

     if( val < 0 ) {

 	val = FIFO_ARR_LENGTH - SCIF_sendq.head + SCIF_sendq.tail;

     }

     return val;

 }

 /**

  * Dequeue one byte from the SCIF transmit queue (ie transmit the byte),

  * updating all status flags as required.

  * @return The byte dequeued, or -1 if the queue is empty.

  */

 int SCIF_sendq_dequeue( )

 {

     uint8_t result;

     uint32_t tmp, length;

     if( SCIF_sendq.head == SCIF_sendq.tail )

 	return -1; /* No data */

     /* Update queue head pointer */

     result = SCIF_sendq.data[SCIF_sendq.head++];

     if( SCIF_sendq.head > FIFO_LENGTH )

 	SCIF_sendq.head = 0;

     /* Update data count register */

     tmp = MMIO_READ( SCIF, SCFDR2 ) & 0x0F;

     length = SCIF_sendq_size();

     MMIO_WRITE( SCIF, SCFDR2, tmp | (length << 8) );

     /* Update status register */

     if( length <= SCIF_sendq.trigger ) {

 	tmp = MMIO_READ( SCIF, SCFSR2 ) | SCFSR2_TDFE;

 	if( length == 0 )

 	    tmp |= SCFSR2_TEND; /* Transmission ended - no data waiting */

 	if( IS_TRANSMIT_IRQ_ENABLED() ) 

 	    intc_raise_interrupt( INT_SCIF_TXI );

         DMAC_trigger( DMAC_SCIF_TDE );

 	MMIO_WRITE( SCIF, SCFSR2, tmp );

     }

     return (int)(unsigned int)result;

 }

 /**

  * Enqueue a single byte in the SCIF transmit queue. If the queue is full,

  * the value will be discarded.

  * @param value to be queued.

  * @param clearFlags TRUE if the TEND/TDFE flags should be cleared

  *   if the queue exceeds the trigger level. (According to the manual,

  *   DMAC writes will clear the flag, whereas regular SH4 writes do NOT

  *   automatically clear it. Go figure).

  * @return gboolean TRUE if the value was queued, FALSE if the queue was

  *   full.

  */

 gboolean SCIF_sendq_enqueue( uint8_t value, gboolean clearFlags )

 {

     uint32_t tmp, length;

     int newpos = SCIF_sendq.tail + 1;

     if( newpos > FIFO_LENGTH )

 	newpos = 0;

     if( newpos == SCIF_sendq.head ) {

 	/* FIFO full - discard */

 	return FALSE;

     }

     SCIF_sendq.data[SCIF_sendq.tail] = value;

     SCIF_sendq.tail = newpos;

     /* Update data count register */

     tmp = MMIO_READ( SCIF, SCFDR2 ) & 0x0F;

     length = SCIF_sendq_size();

     MMIO_WRITE( SCIF, SCFDR2, tmp | (length << 8) );

     /* Update flags if requested */

     if( clearFlags ) {

 	tmp = SCFSR2_TEND;

 	if( length > SCIF_sendq.trigger ) {

 	    tmp |= SCFSR2_TDFE;

 	    if( IS_TRANSMIT_IRQ_ENABLED() )

 		intc_clear_interrupt( INT_SCIF_TXI );

 	}

 	tmp = MMIO_READ( SCIF, SCFSR2 ) & (~tmp);

 	MMIO_WRITE( SCIF, SCFSR2, tmp );

     }

     return TRUE;

 }

 void SCIF_sendq_clear( void ) 

 {

     SCIF_sendq.head = SCIF_sendq.tail = 0;

     MMIO_WRITE( SCIF, SCFDR2, MMIO_READ( SCIF, SCFDR2 ) & 0x0F );

     MMIO_WRITE( SCIF, SCFSR2, MMIO_READ( SCIF, SCFSR2 ) | SCFSR2_TEND | SCFSR2_TDFE );

     if( IS_TRANSMIT_IRQ_ENABLED() ) {

 	intc_raise_interrupt( INT_SCIF_TXI );

         DMAC_trigger( DMAC_SCIF_TDE );

     }

 }

 /**

  * Update the SCFSR2 status register with the given mask (ie clear any values

  * that are set to 0 in the mask. According to a strict reading of the doco

  * though, the bits will only actually clear if the flag state is no longer

  * true, so we need to recheck everything...

  */

 void SCIF_update_status( uint32_t mask )

 {

     uint32_t value = MMIO_READ( SCIF, SCFSR2 );

     uint32_t result = value & mask;

     uint32_t sendq_size = SCIF_sendq_size();

     uint32_t recvq_size = SCIF_recvq_size();

     if( sendq_size != 0 )

 	result |= SCFSR2_TEND;

     if( sendq_size <= SCIF_sendq.trigger )

 	result |= SCFSR2_TDFE;

     else if( (result & SCFSR2_TDFE) == 0 && IS_TRANSMIT_IRQ_ENABLED() )

 	intc_clear_interrupt( INT_SCIF_TXI );

     if( recvq_size >= SCIF_recvq.trigger )

 	result |= SCFSR2_RDF;

     if( (value & SCFSR2_DR) != 0 && (result & SCFSR2_DR) == 0 &&

 	recvq_size != 0 )

 	result |= SCFSR2_DR;

     if( (result & (SCFSR2_DR|SCFSR2_RDF)) == 0 && IS_RECEIVE_IRQ_ENABLED() )

 	intc_clear_interrupt( INT_SCIF_RXI );

     if( IS_RECEIVE_ERROR_IRQ_ENABLED() ) {

 	if( (result & SCFSR2_BRK) == 0 )

 	    intc_clear_interrupt( INT_SCIF_BRI );

 	if( (result & SCFSR2_ER) == 0 && 

 	    (MMIO_READ( SCIF, SCLSR2 ) & SCLSR2_ORER) == 0 )

 	    intc_clear_interrupt( INT_SCIF_ERI );

     }

 }

 /**

  * Set the break detected flag

  */

 void SCIF_set_break( void ) 

 {

     MMIO_WRITE( SCIF, SCFSR2, MMIO_READ( SCIF, SCFSR2 ) | SCFSR2_BRK );

     if( IS_RECEIVE_ERROR_IRQ_ENABLED() )

 	intc_raise_interrupt( INT_SCIF_BRI );

 }

 const static int SCIF_CLOCK_MULTIPLIER[4] = {1, 4, 16, 64};

 /**

  * Calculate the current line speed.

  */

 void SCIF_update_line_speed( void )

 {

     /* If CKE1 is set, use the external clock as a base */

     if( MMIO_READ( SCIF, SCSCR2 ) & SCSCR2_CKE ) {

     } else {

 	/* Otherwise, SH4 peripheral clock divided by n */

 	int mult = SCIF_CLOCK_MULTIPLIER[MMIO_READ( SCIF, SCSMR2 ) & 0x03];

 	/* Then process the bitrate register */

 	int bbr = MMIO_READ( SCIF, SCBRR2 ) & 0xFF;

 	int baudrate = sh4_peripheral_freq / (32 * mult * (bbr+1) );

 	if( serial_device != NULL && serial_device->set_line_speed != NULL )

 	    serial_device->set_line_speed( baudrate );

 	SCIF_tick_period = sh4_peripheral_period * (32 * mult * (bbr+1));

 	/*

 	  clock_set_tick_rate( CLOCK_SCIF, baudrate / 10 );

 	*/

     }

 }

 int32_t mmio_region_SCIF_read( uint32_t reg )

 {

     switch( reg ) {

     case SCFRDR2: /* Receive data */

 	return SCIF_recvq_dequeue(FALSE);

     default:

 	return MMIO_READ( SCIF, reg );

     }

 }

 void mmio_region_SCIF_write( uint32_t reg, uint32_t val ) 

 {

     uint32_t tmp;

     switch( reg ) {

     case SCSMR2: /* Serial mode register */

 	/* Bit 6 => 0 = 8-bit, 1 = 7-bit

 	 * Bit 5 => 0 = Parity disabled, 1 = parity enabled

 	 * Bit 4 => 0 = Even parity, 1 = Odd parity

 	 * Bit 3 => 0 = 1 stop bit, 1 = 2 stop bits

 	 * Bits 0-1 => Clock select 00 = P, 01 = P/4, 10 = P/16, 11 = P/64

 	 */

 	val &= 0x007B;

 	if( serial_device != NULL ) {

 	    serial_device->set_line_params( val );

 	}

 	tmp = MMIO_READ( SCIF, SCSMR2 );

 	if( (tmp & 0x03) != (val & 0x03) ) {

 	    /* Clock change */

 	    SCIF_update_line_speed( );

 	}

 	/* Save for later read-back */

 	MMIO_WRITE( SCIF, SCSMR2, val );

 	break;

     case SCBRR2: /* Bit rate register */

 	MMIO_WRITE( SCIF, SCBRR2, val );

 	SCIF_update_line_speed( );

 	break;

     case SCSCR2: /* Serial control register */

 	/* Bit 7 => Transmit-FIFO-data-empty interrupt enabled 

 	 * Bit 6 => Receive-data-full interrupt enabled 

 	 * Bit 5 => Transmit enable 

 	 * Bit 4 => Receive enable 

 	 * Bit 3 => Receive-error/break interrupt enabled

 	 * Bit 1 => Clock enable

 	 */

 	val &= 0x00FA;

 	/* Clear any interrupts that just became disabled */

 	if( (val & SCSCR2_TIE) == 0 )

 	    intc_clear_interrupt( INT_SCIF_TXI );

 	if( (val & SCSCR2_RIE) == 0 )

 	    intc_clear_interrupt( INT_SCIF_RXI );

 	if( (val & (SCSCR2_RIE|SCSCR2_REIE)) == 0 ) {

 	    intc_clear_interrupt( INT_SCIF_ERI );

 	    intc_clear_interrupt( INT_SCIF_BRI );

 	}

 	MMIO_WRITE( SCIF, reg, val );

 	break;

     case SCFTDR2: /* Transmit FIFO data register */

 	SCIF_sendq_enqueue( val, FALSE );

 	break;

     case SCFSR2: /* Serial status register */

 	/* Bits 12-15 Parity error count

 	 * Bits 8-11 Framing erro count 

 	 * Bit 7 - Receive error

 	 * Bit 6 - Transmit end

 	 * Bit 5 - Transmit FIFO data empty

 	 * Bit 4 - Break detect

 	 * Bit 3 - Framing error

 	 * Bit 2 - Parity error

 	 * Bit 1 - Receive FIFO data full

 	 * Bit 0 - Receive data ready

 	 */

 	/* Clear off any flags/interrupts that are being set to 0 */

 	SCIF_update_status( val );

 	break;

     case SCFCR2: /* FIFO control register */

 	val &= 0x0F;

 	SCIF_recvq.trigger = SCIF_recvq_triggers[val >> 6];

 	SCIF_sendq.trigger = SCIF_sendq_triggers[(val >> 4) & 0x03];

 	if( val & SCFCR2_TFRST ) {

 	    SCIF_sendq_clear();

 	}

 	if( val & SCFCR2_RFRST ) {

 	    SCIF_recvq_clear();

 	}

 	MMIO_WRITE( SCIF, reg, val );

 	break;

     case SCSPTR2: /* Serial Port Register */

 	MMIO_WRITE( SCIF, reg, val );

 	/* NOT IMPLEMENTED */

 	WARN( "SCSPTR2 not implemented: Write %08X", val );

 	break;

     case SCLSR2:

 	val = val & SCLSR2_ORER;

 	if( val == 0 ) {

 	    MMIO_WRITE( SCIF, SCLSR2, val );

 	    if( (MMIO_READ( SCIF, SCFSR2 ) & SCFSR2_ER) == 0 &&

 		IS_RECEIVE_ERROR_IRQ_ENABLED() ) 

 		intc_clear_interrupt( INT_SCIF_ERI );

 	}

 	break;

     }

 }

 /**

  * Actions for a single tick of the serial clock, defined as the transmission

  * time of a single frame.

  *

  * If transmit queue is non-empty:

  *    Transmit one byte and remove from queue

  * If input receive source is non-empty:

  *    Transfer one byte to the receive queue (if queue is full, byte is lost)

  * If recvq is non-empty, less than the trigger level, and no data has been

  *    received in the last 2 ticks (including this one), set the DR flag and

  *    IRQ if appropriate.

  */

 void SCIF_clock_tick( void ) 

 {

     gboolean rcvd = FALSE;

     if( IS_LOOPBACK_ENABLED() ) {

 	if( IS_TRANSMIT_ENABLED() ) {

 	    int val = SCIF_sendq_dequeue();

 	    if( val != -1 && IS_RECEIVE_ENABLED() ) {

 		SCIF_recvq_enqueue( val );

 		rcvd = TRUE;

 	    }

 	}

     } else {

 	if( IS_TRANSMIT_ENABLED() ) {

 	    int val = SCIF_sendq_dequeue();

 	    if( val != -1 && serial_device != NULL && 

 		serial_device->receive_data != NULL ) {

 		serial_device->receive_data( val );

 	    }

 	}

 	if( IS_RECEIVE_ENABLED() ) {

 	    int val = serial_transmit_dequeue();

 	    if( val != -1 ) {

 		SCIF_recvq_enqueue( val );

 		rcvd = TRUE;

 	    }

 	}

     }

     /* Check if we need to set the DR flag */

     if( !rcvd && !SCIF_rcvd_last_tick &&

 	SCIF_recvq.head != SCIF_recvq.tail &&

 	SCIF_recvq_size() < SCIF_recvq.trigger ) {

 	uint32_t tmp = MMIO_READ( SCIF, SCFSR2 );

 	if( (tmp & SCFSR2_DR) == 0 ) {

 	    MMIO_WRITE( SCIF, SCFSR2, tmp | SCFSR2_DR );

 	    if( IS_RECEIVE_IRQ_ENABLED() )

 		intc_raise_interrupt( INT_SCIF_RXI );

 	    DMAC_trigger( DMAC_SCIF_RDF );

 	}

     }

     SCIF_rcvd_last_tick = rcvd;

 }

 void SCIF_reset( void )

 {

     SCIF_recvq_clear();

     SCIF_sendq_clear();

     SCIF_update_line_speed();

 }

 void SCIF_run_slice( uint32_t nanosecs ) 

 {

     SCIF_tick_remainder += nanosecs;

     while( SCIF_tick_remainder >= SCIF_tick_period ) {

 	SCIF_tick_remainder -= SCIF_tick_period;

 	SCIF_clock_tick();

     }

 }