@ -29,38 +29,49 @@
/**
* This is a hybrid system .
*
* The PWM1 module is used to directly control the Servo 0 , 1 & 3 pins . This keeps
* The PWM1 module is used to directly control the Servo 0 , 1 & 3 pins and D9 & D10 pins . This keeps
* the pulse width jitter to under a microsecond .
*
* For all other pins the PWM1 module is used to generate interrupts . The ISR
* routine does the actual setting / clearing of pins . The upside is that any pin can
* have a PWM channel assigned to it . The downside is that there is more pulse width
* jitter . The jitter depends on what else is happening in the system and what ISRs
* prempt the PWM ISR . Writing to the SD card can add 20 microseconds to the pulse
* width .
* pre - empt the PWM ISR .
*/
/**
* The data structures are setup to minimize the computation done by the ISR which
* minimizes ISR execution time . Execution times are 2.2 - 3.7 microseconds .
* The data structures are set up to minimize the computation done by the ISR which
* minimizes ISR execution time . Execution times are 2 - 4 µ s except when updating to
* a new value when they are 19 µ s .
*
* Two tables are used . active_table is used by the ISR . Changes to the table are
* are done by copying the active_table into the work_table , updating the work_table
* and then swapping the two tables . Swapping is done by manipulating pointers .
* Two tables are used . One table contains the data used by the ISR to update / control
* the PWM pins . The other is used as an aid when rebuilding the ISR table .
*
* Immediately after the swap the ISR uses the work_table until the start of the
* next 20 mS cycle . During this transition the " work_table " is actually the table
* that was being used before the swap . The " active_table " contains the data that
* will start being used at the start of the next 20 mS period . This keeps the pins
* well behaved during the transition .
* The LPC1768_PWM_attach_pin routine disables the ISR and then adds the new info to
* ISR table . It can update the table directly because none of its changes affect
* what the ISR does .
*
* The ISR ' s priority is set to the maximum otherwise other ISRs can cause considerable
* jitter in the PWM high time .
* LPC1768_PWM_detach_pin routine disables the ISR , disables the pin immediately if
* it ' s a directly controlled pin and updates the helper table . It then flags the
* ISR that the ISR table needs to be rebuilt .
*
* LPC1768_PWM_write routine disables the ISR and updates the helper table . It then
* flags the ISR that the ISR table needs to be rebuilt .
*
* The ISR ' s priority is set to less than the stepper ISR otherwise it could cause jitter
* in the step pulses .
*
* See the end of this file for details on the hardware / firmware interaction
*/
# ifdef TARGET_LPC1768
# include "../../inc/MarlinConfig.h"
// #include <math.h>
// #include <stdio.h>
// #include <stdlib.h>
# include <lpc17xx_pinsel.h>
# include "LPC1768_PWM.h"
# include "arduino.h"
@ -68,48 +79,68 @@
# define NUM_PWMS 6
typedef struct { // holds all data needed to control/init one of the PWM channels
uint8_t sequence ; // 0: available slot, 1 - 6: PWM channel assigned to that slot
pin_t pin ;
uint16_t PWM_mask ; // MASK TO CHECK/WRITE THE IR REGISTER
volatile uint32_t * set_register ;
volatile uint32_t * clr_register ;
uint32_t write_mask ; // USED BY SET/CLEAR COMMANDS
uint32_t microseconds ; // value written to MR register
uint32_t min ; // lower value limit checked by WRITE routine before writing to the MR register
uint32_t max ; // upper value limit checked by WRITE routine before writing to the MR register
bool PWM_flag ; // 0 - USED BY sERVO , 1 - USED BY ANALOGWRITE
uint8_t servo_index ; // 0 - MAX_SERVO -1 : servo index, 0xFF : PWM channel
bool active_flag ; // THIS TABLE ENTRY IS ACTIVELY TOGGLING A PIN
uint8_t assigned_MR ; // Which MR (1-6) is used by this logical channel
uint32_t PCR_bit ; // PCR register bit to enable PWM1 control of this pin
uint32_t PINSEL3 _bits ; // PINSEL3 register bits to set pin mode to PWM1 control
uint8_t sequence ; // 0: available slot, 1 - 6: PWM channel assigned to that slot
pin_t pin ;
uint16_t PWM_mask ; // MASK TO CHECK/WRITE THE IR REGISTER
volatile uint32_t * set_register ;
volatile uint32_t * clr_register ;
uint32_t write_mask ; // USED BY SET/CLEAR COMMANDS
uint32_t microseconds ; // value written to MR register
uint32_t min ; // lower value limit checked by WRITE routine before writing to the MR register
uint32_t max ; // upper value limit checked by WRITE routine before writing to the MR register
bool PWM_flag ; // 0 - USED BY hardware PWM , 1 - USED BY ANALOGWRITE
uint8_t servo_index ; // 0 - MAX_SERVO -1 : servo index, 0xFF : PWM channel
bool active_flag ; // THIS TABLE ENTRY IS ACTIVELY TOGGLING A PIN
uint32_t PCR_bit ; // PCR register bit to enable PWM1 control of this pin
volatile uint32_t * PINSEL_reg ; // PINSEL register
uint32_t PINSEL_bits ; // PINSEL register bits to set pin mode to PWM1 control
} PWM_map ;
# define MICRO_MAX 0xffffffff
# define MICRO_MAX 0xFFFFFFFF
# define PWM_MAP_INIT_ROW {0, P_NC, 0, 0, 0, 0, MICRO_MAX, 0, 0, 0, 0, 0, 0, 0, 0}
# define PWM_MAP_INIT {PWM_MAP_INIT_ROW,\
PWM_MAP_INIT_ROW , \
PWM_MAP_INIT_ROW , \
PWM_MAP_INIT_ROW , \
PWM_MAP_INIT_ROW , \
PWM_MAP_INIT_ROW , \
# define PWM_MAP_INIT_ROW { 0, 0x7FFF, 0, 0, 0, 0, MICRO_MAX, 0, 0, 0, 0, 0, 0, 0, 0 }
# define PWM_MAP_INIT { PWM_MAP_INIT_ROW, PWM_MAP_INIT_ROW, PWM_MAP_INIT_ROW, \
PWM_MAP_INIT_ROW , PWM_MAP_INIT_ROW , PWM_MAP_INIT_ROW , \
} ;
PWM_map PWM1_map_A [ NUM_PWMS ] = PWM_MAP_INIT ;
PWM_map PWM1_map_B [ NUM_PWMS ] = PWM_MAP_INIT ;
PWM_map ISR_table [ NUM_PWMS ] = PWM_MAP_INIT ;
PWM_map * active_table = PWM1_map_A ;
PWM_map * work_table = PWM1_map_B ;
PWM_map * ISR_table ;
# define IR_BIT(p) ((p) >= 0 && (p) <= 3 ? (p) : p + 4 )
# define PIN_IS_INVERTED(p) 0 // placeholder in case inverting PWM output is offered
# define IR_BIT(p) (p >= 0 && p <= 3 ? p : p + 4 )
# define COPY_ACTIVE_TABLE for (uint8_t i = 0; i < 6 ; i++) work_table[i] = active_table[i]
# define PIN_IS_INVERTED(p) 0 // place holder in case inverting PWM output is offered
# define P1_18_PWM_channel 1 // servo 3
# define P1_20_PWM_channel 2 // servo 0
# define P1_21_PWM_channel 3 // servo 1
# define P2_4_PWM_channel 5 // D9
# define P2_5_PWM_channel 6 // D10
// used to keep track of which Match Registers have been used and if they will be used by the
// PWM1 module to directly control the pin or will be used to generate an interrupt
typedef struct { // status of PWM1 channel
uint8_t map_used ; // 0 - this MR register not used/assigned
uint8_t map_PWM_INT ; // 0 - available for interrupts, 1 - in use by PWM
pin_t map_PWM_PIN ; // pin for this PwM1 controlled pin / port
volatile uint32_t * MR_register ; // address of the MR register for this PWM1 channel
uint32_t PCR_bit ; // PCR register bit to enable PWM1 control of this pin
// 0 - don't switch to PWM1 direct control
volatile uint32_t * PINSEL_reg ; // PINSEL register
uint32_t PINSEL_bits ; // PINSEL register bits to set pin mode to PWM1 control
} MR_map ;
MR_map map_MR [ NUM_PWMS ] ;
void LPC1768_PWM_update_map_MR ( void ) {
map_MR [ 0 ] = { 0 , ( uint8_t ) ( LPC_PWM1 - > PCR & _BV ( 8 + P1_18_PWM_channel ) ? 1 : 0 ) , P1_18 , & LPC_PWM1 - > MR1 , 0 , 0 , 0 } ;
map_MR [ 1 ] = { 0 , ( uint8_t ) ( LPC_PWM1 - > PCR & _BV ( 8 + P1_20_PWM_channel ) ? 1 : 0 ) , P1_20 , & LPC_PWM1 - > MR2 , 0 , 0 , 0 } ;
map_MR [ 2 ] = { 0 , ( uint8_t ) ( LPC_PWM1 - > PCR & _BV ( 8 + P1_21_PWM_channel ) ? 1 : 0 ) , P1_21 , & LPC_PWM1 - > MR3 , 0 , 0 , 0 } ;
map_MR [ 3 ] = { 0 , 0 , P_NC , & LPC_PWM1 - > MR4 , 0 , 0 , 0 } ;
map_MR [ 4 ] = { 0 , ( uint8_t ) ( LPC_PWM1 - > PCR & _BV ( 8 + P2_4_PWM_channel ) ? 1 : 0 ) , P2_4 , & LPC_PWM1 - > MR5 , 0 , 0 , 0 } ;
map_MR [ 5 ] = { 0 , ( uint8_t ) ( LPC_PWM1 - > PCR & _BV ( 8 + P2_5_PWM_channel ) ? 1 : 0 ) , P2_5 , & LPC_PWM1 - > MR6 , 0 , 0 , 0 } ;
}
/**
* Prescale register and MR0 register values
@ -144,317 +175,322 @@ PWM_map *ISR_table;
*
*/
bool ISR_table_update = false ; // flag to tell the ISR that the tables need to be updated & swapped
void LPC1768_PWM_init ( void ) {
# define SBIT_CNTEN 0 // PWM1 counter & pre-scaler enable/disable
# define SBIT_CNTRST 1 // reset counters to known state
# define SBIT_PWMEN 3 // 1 - PWM, 0 - timer
# define SBIT_PWMMR0R 1
# define PCPWM1 6
# define SBIT_CNTEN 0 // PWM1 counter & pre-scaler enable/disable
# define SBIT_CNTRST 1 // reset counters to known state
# define SBIT_PWMEN 3 // 1 - PWM, 0 - timer
# define SBIT_PWMMR0R 1
# define PCPWM1 6
# define PCLK_PWM1 12
LPC_SC - > PCONP | = ( 1 < < PCPWM1 ) ; // e nable PWM1 controller (enabled on power up)
SBI ( LPC_SC - > PCONP , PCPWM1 ) ; // E nable PWM1 controller (enabled on power up)
LPC_SC - > PCLKSEL0 & = ~ ( 0x3 < < PCLK_PWM1 ) ;
LPC_SC - > PCLKSEL0 | = ( LPC_PWM1_PCLKSEL0 < < PCLK_PWM1 ) ;
LPC_PWM1 - > MR0 = LPC_PWM1_MR0 ; // TC resets every 19,999 + 1 cycles - sets PWM cycle(Ton+Toff) to 20 mS
// MR0 must be set before TCR enables the PWM
LPC_PWM1 - > TCR = _BV ( SBIT_CNTEN ) | _BV ( SBIT_CNTRST ) | _BV ( SBIT_PWMEN ) ; ; // enable counters, reset counters, set mode to PWM
LPC_PWM1 - > TCR & = ~ ( _BV ( SBIT_CNTRST ) ) ; // take counters out of reset
LPC_PWM1 - > PR = LPC_PWM1_PR ;
LPC_PWM1 - > MCR = ( _BV ( SBIT_PWMMR0R ) | _BV ( 0 ) ) ; // Reset TC if it matches MR0, disable all interrupts except for MR0
LPC_PWM1 - > CTCR = 0 ; // disable counter mode (enable PWM mode)
LPC_PWM1 - > LER = 0x07F ; // Set the latch Enable Bits to load the new Match Values for MR0 - MR6
// Set all PWMs to single edge
LPC_PWM1 - > PCR = 0 ; // single edge mode for all channels, PWM1 control of outputs off
NVIC_EnableIRQ ( PWM1_IRQn ) ; // Enable interrupt handler
// NVIC_SetPriority(PWM1_IRQn, NVIC_EncodePriority(0, 10, 0)); // normal priority for PWM module
NVIC_SetPriority ( PWM1_IRQn , NVIC_EncodePriority ( 0 , 0 , 0 ) ) ; // minimizes jitter due to higher priority ISRs
LPC_PWM1 - > MR0 = LPC_PWM1_MR0 ; // TC resets every 19,999 + 1 cycles - sets PWM cycle(Ton+Toff) to 20 mS
// MR0 must be set before TCR enables the PWM
LPC_PWM1 - > TCR = _BV ( SBIT_CNTEN ) | _BV ( SBIT_CNTRST ) | _BV ( SBIT_PWMEN ) ; // Enable counters, reset counters, set mode to PWM
LPC_PWM1 - > TCR & = ~ ( _BV ( SBIT_CNTRST ) ) ; // Take counters out of reset
LPC_PWM1 - > PR = LPC_PWM1_PR ;
LPC_PWM1 - > MCR = _BV ( SBIT_PWMMR0R ) | _BV ( 0 ) ; // Reset TC if it matches MR0, disable all interrupts except for MR0
LPC_PWM1 - > CTCR = 0 ; // Disable counter mode (enable PWM mode)
LPC_PWM1 - > LER = 0x07F ; // Set the latch Enable Bits to load the new Match Values for MR0 - MR6
LPC_PWM1 - > PCR = 0 ; // Single edge mode for all channels, PWM1 control of outputs off
NVIC_EnableIRQ ( PWM1_IRQn ) ; // Enable interrupt handler
NVIC_SetPriority ( PWM1_IRQn , NVIC_EncodePriority ( 0 , 10 , 0 ) ) ; // Normal priority for PWM module
//NVIC_SetPriority(PWM1_IRQn, NVIC_EncodePriority(0, 0, 0)); // Minimizes jitter due to higher priority ISRs
}
bool PWM_table_swap = false ; // flag to tell the ISR that the tables have been swapped
bool PWM_MR0_wait = false ; // flag to ensure don't delay MR0 interrupt
bool LPC1768_PWM_attach_pin ( pin_t pin , uint32_t min /* = 1 */ , uint32_t max /* = (LPC_PWM1_MR0 - MR0_MARGIN) */ , uint8_t servo_index /* = 0xff */ ) {
pin = GET_PIN_MAP_PIN ( GET_PIN_MAP_INDEX ( pin & 0xFF ) ) ; // Sometimes the upper byte is garbled
bool LPC1768_PWM_attach_pin ( pin_t pin , uint32_t min /* = 1 */ , uint32_t max /* = (LPC_PWM1_MR0 - MR0_MARGIN) */ , uint8_t servo_index /* = 0xff */ ) {
while ( PWM_table_swap ) delay ( 5 ) ; // don't do anything until the previous change has been implemented by the ISR
COPY_ACTIVE_TABLE ; // copy active table into work table
NVIC_DisableIRQ ( PWM1_IRQn ) ; // make it safe to update the active table
// OK to update the active table because the
// ISR doesn't use any of the changed items
uint8_t slot = 0 ;
for ( uint8_t i = 0 ; i < NUM_PWMS ; i + + ) // see if already in table
if ( work_table [ i ] . pin = = pin ) return 1 ;
if ( ISR_table [ i ] . pin = = pin ) {
NVIC_EnableIRQ ( PWM1_IRQn ) ; // re-enable PWM interrupts
return 1 ;
}
for ( uint8_t i = 1 ; ( i < NUM_PWMS + 1 ) & & ! slot ; i + + ) // find empty slot
if ( ! ( work_table [ i - 1 ] . set_register ) ) slot = i ; // any item that can't be zero when active or just attached is OK
if ( ! ( ISR _table[ i - 1 ] . set_register ) ) { slot = i ; break ; } // any item that can't be zero when active or just attached is OK
if ( ! slot ) return 0 ;
slot - - ; // turn it into array index
work_table [ slot ] . pin = pin ; // init slot
work_table [ slot ] . PWM_mask = 0 ; // real value set by PWM_write
work_table [ slot ] . set_register = PIN_IS_INVERTED ( pin ) ? & LPC_GPIO ( LPC1768_PIN_PORT ( pin ) ) - > FIOCLR : & LPC_GPIO ( LPC1768_PIN_PORT ( pin ) ) - > FIOSET ;
work_table [ slot ] . clr_register = PIN_IS_INVERTED ( pin ) ? & LPC_GPIO ( LPC1768_PIN_PORT ( pin ) ) - > FIOSET : & LPC_GPIO ( LPC1768_PIN_PORT ( pin ) ) - > FIOCLR ;
work_table [ slot ] . write_mask = LPC_PIN ( LPC1768_PIN_PIN ( pin ) ) ;
work_table [ slot ] . microseconds = MICRO_MAX ;
work_table [ slot ] . min = min ;
work_table [ slot ] . max = MIN ( max , LPC_PWM1_MR0 - MR0_MARGIN ) ;
work_table [ slot ] . servo_index = servo_index ;
work_table [ slot ] . active_flag = false ;
//swap tables
PWM_MR0_wait = true ;
while ( PWM_MR0_wait ) delay ( 5 ) ; //wait until MR0 interrupt has happend so don't delay it.
ISR_table [ slot ] . pin = pin ; // init slot
ISR_table [ slot ] . PWM_mask = 0 ; // real value set by PWM_write
ISR_table [ slot ] . set_register = PIN_IS_INVERTED ( pin ) ? & LPC_GPIO ( LPC1768_PIN_PORT ( pin ) ) - > FIOCLR : & LPC_GPIO ( LPC1768_PIN_PORT ( pin ) ) - > FIOSET ;
ISR_table [ slot ] . clr_register = PIN_IS_INVERTED ( pin ) ? & LPC_GPIO ( LPC1768_PIN_PORT ( pin ) ) - > FIOSET : & LPC_GPIO ( LPC1768_PIN_PORT ( pin ) ) - > FIOCLR ;
ISR_table [ slot ] . write_mask = LPC_PIN ( LPC1768_PIN_PIN ( pin ) ) ;
ISR_table [ slot ] . microseconds = MICRO_MAX ;
ISR_table [ slot ] . min = min ;
ISR_table [ slot ] . max = MIN ( max , LPC_PWM1_MR0 - MR0_MARGIN ) ;
ISR_table [ slot ] . servo_index = servo_index ;
ISR_table [ slot ] . active_flag = false ;
NVIC_DisableIRQ ( PWM1_IRQn ) ;
PWM_map * pointer_swap = active_table ;
active_table = work_table ;
work_table = pointer_swap ;
PWM_table_swap = true ; // tell the ISR that the tables have been swapped
NVIC_EnableIRQ ( PWM1_IRQn ) ; // re-enable PWM interrupts
return 1 ;
}
# define pin_11_PWM_channel 2
# define pin_6_PWM_channel 3
# define pin_4_PWM_channel 1
// used to keep track of which Match Registers have been used and if they will be used by the
// PWM1 module to directly control the pin or will be used to generate an interrupt
typedef struct { // status of PWM1 channel
uint8_t map_used ; // 0 - this MR register not used/assigned
uint8_t map_PWM_INT ; // 0 - available for interrupts, 1 - in use by PWM
pin_t map_PWM_PIN ; // pin for this PwM1 controlled pin / port
volatile uint32_t * MR_register ; // address of the MR register for this PWM1 channel
uint32_t PCR_bit ; // PCR register bit to enable PWM1 control of this pin
uint32_t PINSEL3_bits ; // PINSEL3 register bits to set pin mode to PWM1 control
} MR_map ;
bool LPC1768_PWM_detach_pin ( pin_t pin ) {
MR_map map_MR [ NUM_PWMS ] ;
pin = GET_PIN_MAP_PIN ( GET_PIN_MAP_INDEX ( pin & 0xFF ) ) ;
void LPC1768_PWM_update_map_MR ( void ) {
map_MR [ 0 ] = { 0 , ( uint8_t ) ( LPC_PWM1 - > PCR & _BV ( 8 + pin_4_PWM_channel ) ? 1 : 0 ) , P1_18 , & LPC_PWM1 - > MR1 , 0 , 0 } ;
map_MR [ 1 ] = { 0 , ( uint8_t ) ( LPC_PWM1 - > PCR & _BV ( 8 + pin_11_PWM_channel ) ? 1 : 0 ) , P1_20 , & LPC_PWM1 - > MR2 , 0 , 0 } ;
map_MR [ 2 ] = { 0 , ( uint8_t ) ( LPC_PWM1 - > PCR & _BV ( 8 + pin_6_PWM_channel ) ? 1 : 0 ) , P1_21 , & LPC_PWM1 - > MR3 , 0 , 0 } ;
map_MR [ 3 ] = { 0 , 0 , P_NC , & LPC_PWM1 - > MR4 , 0 , 0 } ;
map_MR [ 4 ] = { 0 , 0 , P_NC , & LPC_PWM1 - > MR5 , 0 , 0 } ;
map_MR [ 5 ] = { 0 , 0 , P_NC , & LPC_PWM1 - > MR6 , 0 , 0 } ;
}
NVIC_EnableIRQ ( PWM1_IRQn ) ; // ?? fixes compiler problem?? ISR won't start
// unless put in an extra "enable"
NVIC_DisableIRQ ( PWM1_IRQn ) ;
uint8_t slot = 0xFF ;
for ( uint8_t i = 0 ; i < NUM_PWMS ; i + + ) // find slot
if ( ISR_table [ i ] . pin = = pin ) { slot = i ; break ; }
if ( slot = = 0xFF ) return false ; // return error if pin not found
uint32_t LPC1768_PWM_interrupt_mask = 1 ;
LPC1768_PWM_update_map_MR ( ) ;
void LPC1768_PWM_update ( void ) {
for ( uint8_t i = NUM_PWMS ; - - i ; ) { // (bubble) sort table by microseconds
bool didSwap = false ;
PWM_map temp ;
for ( uint16_t j = 0 ; j < i ; + + j ) {
if ( work_table [ j ] . microseconds > work_table [ j + 1 ] . microseconds ) {
temp = work_table [ j + 1 ] ;
work_table [ j + 1 ] = work_table [ j ] ;
work_table [ j ] = temp ;
didSwap = true ;
}
}
if ( ! didSwap ) break ;
// OK to make these changes before the MR0 interrupt
switch ( pin ) {
case P1_20 : // Servo 0, PWM1 channel 2 (Pin 11 P1.20 PWM1.2)
LPC_PWM1 - > PCR & = ~ ( _BV ( 8 + P1_20_PWM_channel ) ) ; // disable PWM1 module control of this pin
map_MR [ P1_20_PWM_channel - 1 ] . PCR_bit = 0 ;
LPC_PINCON - > PINSEL3 & = ~ ( 0x3 < < 8 ) ; // return pin to general purpose I/O
map_MR [ P1_20_PWM_channel - 1 ] . PINSEL_bits = 0 ;
map_MR [ P1_20_PWM_channel - 1 ] . map_PWM_INT = 0 ; // 0 - available for interrupts, 1 - in use by PWM
break ;
case P1_21 : // Servo 1, PWM1 channel 3 (Pin 6 P1.21 PWM1.3)
LPC_PWM1 - > PCR & = ~ ( _BV ( 8 + P1_21_PWM_channel ) ) ; // disable PWM1 module control of this pin
map_MR [ P1_21_PWM_channel - 1 ] . PCR_bit = 0 ;
LPC_PINCON - > PINSEL3 & = ~ ( 0x3 < < 10 ) ; // return pin to general purpose I/O
map_MR [ P1_21_PWM_channel - 1 ] . PINSEL_bits = 0 ;
map_MR [ P1_21_PWM_channel - 1 ] . map_PWM_INT = 0 ; // 0 - available for interrupts, 1 - in use by PWM
break ;
case P1_18 : // Servo 3, PWM1 channel 1 (Pin 4 P1.18 PWM1.1)
LPC_PWM1 - > PCR & = ~ ( _BV ( 8 + P1_18_PWM_channel ) ) ; // disable PWM1 module control of this pin
map_MR [ P1_18_PWM_channel - 1 ] . PCR_bit = 0 ;
LPC_PINCON - > PINSEL3 & = ~ ( 0x3 < < 4 ) ; // return pin to general purpose I/O
map_MR [ P1_18_PWM_channel - 1 ] . PINSEL_bits = 0 ;
map_MR [ P1_18_PWM_channel - 1 ] . map_PWM_INT = 0 ; // 0 - available for interrupts, 1 - in use by PWM
break ;
case P2_4 : // D9 FET, PWM1 channel 5 (Pin 9 P2_4 PWM1.5)
LPC_PWM1 - > PCR & = ~ ( _BV ( 8 + P2_4_PWM_channel ) ) ; // disable PWM1 module control of this pin
map_MR [ P2_4_PWM_channel - 1 ] . PCR_bit = 0 ;
LPC_PINCON - > PINSEL4 & = ~ ( 0x3 < < 10 ) ; // return pin to general purpose I/O
map_MR [ P2_4_PWM_channel - 1 ] . PINSEL_bits = 0 ;
map_MR [ P2_4_PWM_channel - 1 ] . map_PWM_INT = 0 ; // 0 - available for interrupts, 1 - in use by PWM
break ;
case P2_5 : // D10 FET, PWM1 channel 6 (Pin 10 P2_5 PWM1.6)
LPC_PWM1 - > PCR & = ~ ( _BV ( 8 + P2_5_PWM_channel ) ) ; // disable PWM1 module control of this pin
map_MR [ P2_5_PWM_channel - 1 ] . PCR_bit = 0 ;
LPC_PINCON - > PINSEL4 & = ~ ( 0x3 < < 4 ) ; // return pin to general purpose I/O
map_MR [ P2_5_PWM_channel - 1 ] . PINSEL_bits = 0 ;
map_MR [ P2_5_PWM_channel - 1 ] . map_PWM_INT = 0 ; // 0 - available for interrupts, 1 - in use by PWM
break ;
default :
break ;
}
LPC1768_PWM_interrupt_mask = 0 ; // set match registers to new values, build IRQ mask
for ( uint8_t i = 0 ; i < NUM_PWMS ; i + + ) {
if ( work_table [ i ] . active_flag = = true ) {
work_table [ i ] . sequence = i + 1 ;
ISR_table [ slot ] = PWM_MAP_INIT_ROW ;
// first see if there is a PWM1 controlled pin for this entry
bool found = false ;
for ( uint8_t j = 0 ; ( j < NUM_PWMS ) & & ! found ; j + + ) {
if ( ( map_MR [ j ] . map_PWM_PIN = = work_table [ i ] . pin ) & & map_MR [ j ] . map_PWM_INT ) {
* map_MR [ j ] . MR_register = work_table [ i ] . microseconds ; // found one of the PWM pins
work_table [ i ] . PWM_mask = 0 ;
work_table [ i ] . PCR_bit = map_MR [ j ] . PCR_bit ; // PCR register bit to enable PWM1 control of this pin
work_table [ i ] . PINSEL3_bits = map_MR [ j ] . PINSEL3_bits ; // PINSEL3 register bits to set pin mode to PWM1 control} MR_map;
map_MR [ j ] . map_used = 2 ;
work_table [ i ] . assigned_MR = j + 1 ; // only used to help in debugging
found = true ;
}
}
ISR_table_update = true ;
NVIC_EnableIRQ ( PWM1_IRQn ) ; // re-enable PWM interrupts
// didn't find a PWM1 pin so get an interrupt
for ( uint8_t k = 0 ; ( k < NUM_PWMS ) & & ! found ; k + + ) {
if ( ! ( map_MR [ k ] . map_PWM_INT | | map_MR [ k ] . map_used ) ) {
* map_MR [ k ] . MR_register = work_table [ i ] . microseconds ; // found one for an interrupt pin
map_MR [ k ] . map_used = 1 ;
LPC1768_PWM_interrupt_mask | = _BV ( 3 * ( k + 1 ) ) ; // set bit in the MCR to enable this MR to generate an interrupt
work_table [ i ] . PWM_mask = _BV ( IR_BIT ( k + 1 ) ) ; // bit in the IR that will go active when this MR generates an interrupt
work_table [ i ] . assigned_MR = k + 1 ; // only used to help in debugging
found = true ;
}
}
}
else
work_table [ i ] . sequence = 0 ;
}
LPC1768_PWM_interrupt_mask | = ( uint32_t ) _BV ( 0 ) ; // add in MR0 interrupt
return 1 ;
}
// swap tables
PWM_MR0_wait = true ;
while ( PWM_MR0_wait ) delay ( 5 ) ; //wait until MR0 interrupt has happend so don't delay it.
bool LPC1768_PWM_write ( pin_t pin , uint32_t value ) {
NVIC_DisableIRQ ( PWM1_IRQn ) ;
LPC_PWM1 - > LER = 0x07E ; // Set the latch Enable Bits to load the new Match Values for MR1 - MR6
PWM_map * pointer_swap = active_table ;
active_table = work_table ;
work_table = pointer_swap ;
PWM_table_swap = true ; // tell the ISR that the tables have been swapped
NVIC_EnableIRQ ( PWM1_IRQn ) ; // re-enable PWM interrupts
}
pin = GET_PIN_MAP_PIN ( GET_PIN_MAP_INDEX ( pin & 0xFF ) ) ;
NVIC_DisableIRQ ( PWM1_IRQn ) ;
bool LPC1768_PWM_write ( pin_t pin , uint32_t value ) {
while ( PWM_table_swap ) delay ( 5 ) ; // don't do anything until the previous change has been implemented by the ISR
COPY_ACTIVE_TABLE ; // copy active table into work table
uint8_t slot = 0xFF ;
for ( uint8_t i = 0 ; i < NUM_PWMS ; i + + ) // find slot
if ( work _table[ i ] . pin = = pin ) slot = i ;
if ( ISR_table [ i ] . pin = = pin ) { slot = i ; break ; }
if ( slot = = 0xFF ) return false ; // return error if pin not found
LPC1768_PWM_update_map_MR ( ) ;
switch ( pin ) {
case P1_20 : // Servo 0, PWM1 channel 2 (Pin 11 P1.20 PWM1.2)
map_MR [ pin_11 _PWM_channel - 1 ] . PCR_bit = _BV ( 8 + pin_11 _PWM_channel) ; // enable PWM1 module control of this pin
map_MR [ pin_11 _PWM_channel - 1 ] . map_PWM_INT = 1 ; // 0 - available for interrupts, 1 - in use by PWM
map_MR [ pin_11 _PWM_channel - 1 ] . PINSEL3 _bits = 0x2 < < 8 ; // ISR must do this AFTER setting PCR
map_MR [ P1_20 _PWM_channel - 1 ] . PCR_bit = _BV ( 8 + P1_20 _PWM_channel) ; // enable PWM1 module control of this pin
map_MR [ P1_20 _PWM_channel - 1 ] . PINSEL_reg = & LPC_PINCON - > PINSEL3 ;
map_MR [ P1_20 _PWM_channel - 1 ] . PINSEL_bits = 0x2 < < 8 ; // ISR must do this AFTER setting PCR
break ;
case P1_21 : // Servo 1, PWM1 channel 3 (Pin 6 P1.21 PWM1.3)
map_MR [ pin_6 _PWM_channel - 1 ] . PCR_bit = _BV ( 8 + pin_6 _PWM_channel) ; // enable PWM1 module control of this pin
map_MR [ pin_6 _PWM_channel - 1 ] . map_PWM_INT = 1 ; // 0 - available for interrupts, 1 - in use by PWM
map_MR [ pin_6 _PWM_channel - 1 ] . PINSEL3 _bits = 0x2 < < 10 ; // ISR must do this AFTER setting PCR
map_MR [ P1_21 _PWM_channel - 1 ] . PCR_bit = _BV ( 8 + P1_21 _PWM_channel) ; // enable PWM1 module control of this pin
map_MR [ P1_21 _PWM_channel - 1 ] . PINSEL_reg = & LPC_PINCON - > PINSEL3 ;
map_MR [ P1_21 _PWM_channel - 1 ] . PINSEL_bits = 0x2 < < 10 ; // ISR must do this AFTER setting PCR
break ;
case P1_18 : // Servo 3, PWM1 channel 1 (Pin 4 P1.18 PWM1.1)
map_MR [ pin_4_PWM_channel - 1 ] . PCR_bit = _BV ( 8 + pin_4_PWM_channel ) ; // enable PWM1 module control of this pin
map_MR [ pin_4_PWM_channel - 1 ] . map_PWM_INT = 1 ; // 0 - available for interrupts, 1 - in use by PWM
map_MR [ pin_4_PWM_channel - 1 ] . PINSEL3_bits = 0x2 < < 4 ; // ISR must do this AFTER setting PCR
map_MR [ P1_18_PWM_channel - 1 ] . PCR_bit = _BV ( 8 + P1_18_PWM_channel ) ; // enable PWM1 module control of this pin
map_MR [ P1_18_PWM_channel - 1 ] . PINSEL_reg = & LPC_PINCON - > PINSEL3 ;
map_MR [ P1_18_PWM_channel - 1 ] . PINSEL_bits = 0x2 < < 4 ; // ISR must do this AFTER setting PCR
break ;
case P2_4 : // D9 FET, PWM1 channel 5 (Pin 9 P2_4 PWM1.5)
map_MR [ P2_4_PWM_channel - 1 ] . PCR_bit = _BV ( 8 + P2_4_PWM_channel ) ; // enable PWM1 module control of this pin
map_MR [ P2_4_PWM_channel - 1 ] . PINSEL_reg = & LPC_PINCON - > PINSEL4 ;
map_MR [ P2_4_PWM_channel - 1 ] . PINSEL_bits = 0x1 < < 8 ; // ISR must do this AFTER setting PCR
break ;
case P2_5 : // D10 FET, PWM1 channel 6 (Pin 10 P2_5 PWM1.6)
map_MR [ P2_5_PWM_channel - 1 ] . PCR_bit = _BV ( 8 + P2_5_PWM_channel ) ; // enable PWM1 module control of this pin
map_MR [ P2_5_PWM_channel - 1 ] . PINSEL_reg = & LPC_PINCON - > PINSEL4 ;
map_MR [ P2_5_PWM_channel - 1 ] . PINSEL_bits = 0x1 < < 10 ; // ISR must do this AFTER setting PCR
break ;
default : // ISR pins
pinMode ( pin , OUTPUT ) ; // set pin to output but don't write anything in case it's already in use
default : // ISR pins
pinMode ( pin , OUTPUT ) ; // set pin to output
break ;
}
work_table [ slot ] . microseconds = MAX ( MIN ( value , work_table [ slot ] . max ) , work_table [ slot ] . min ) ;
work_table [ slot ] . active_flag = true ;
ISR _table[ slot ] . microseconds = MAX ( MIN ( value , ISR _table[ slot ] . max ) , ISR _table[ slot ] . min ) ;
ISR _table[ slot ] . active_flag = 1 ;
LPC1768_PWM_update ( ) ;
ISR_table_update = true ;
NVIC_EnableIRQ ( PWM1_IRQn ) ; // re-enable PWM interrupts
return 1 ;
}
bool LPC1768_PWM_detach_pin ( pin_t pin ) {
while ( PWM_table_swap ) delay ( 5 ) ; // don't do anything until the previous change has been implemented by the ISR
COPY_ACTIVE_TABLE ; // copy active table into work table
uint8_t slot = 0xFF ;
for ( uint8_t i = 0 ; i < NUM_PWMS ; i + + ) // find slot
if ( work_table [ i ] . pin = = pin ) slot = i ;
if ( slot = = 0xFF ) return false ; // return error if pin not found
uint32_t LPC1768_PWM_interrupt_mask = 1 ;
LPC1768_PWM_update_map_MR ( ) ;
// OK to make these changes before the MR0 interrupt
switch ( pin ) {
case P1_20 : // Servo 0, PWM1 channel 2 (Pin 11 P1.20 PWM1.2)
LPC_PWM1 - > PCR & = ~ ( _BV ( 8 + pin_11_PWM_channel ) ) ; // disable PWM1 module control of this pin
map_MR [ pin_11_PWM_channel - 1 ] . PCR_bit = 0 ;
LPC_PINCON - > PINSEL3 & = ~ ( 0x3 < < 8 ) ; // return pin to general purpose I/O
map_MR [ pin_11_PWM_channel - 1 ] . PINSEL3_bits = 0 ;
map_MR [ pin_11_PWM_channel - 1 ] . map_PWM_INT = 0 ; // 0 - available for interrupts, 1 - in use by PWM
break ;
case P1_21 : // Servo 1, PWM1 channel 3 (Pin 6 P1.21 PWM1.3)
LPC_PWM1 - > PCR & = ~ ( _BV ( 8 + pin_6_PWM_channel ) ) ; // disable PWM1 module control of this pin
map_MR [ pin_6_PWM_channel - 1 ] . PCR_bit = 0 ;
LPC_PINCON - > PINSEL3 & = ~ ( 0x3 < < 10 ) ; // return pin to general purpose I/O
map_MR [ pin_6_PWM_channel - 1 ] . PINSEL3_bits = 0 ;
map_MR [ pin_6_PWM_channel - 1 ] . map_PWM_INT = 0 ; // 0 - available for interrupts, 1 - in use by PWM
break ;
case P1_18 : // Servo 3, PWM1 channel 1 (Pin 4 P1.18 PWM1.1)
LPC_PWM1 - > PCR & = ~ ( _BV ( 8 + pin_4_PWM_channel ) ) ; // disable PWM1 module control of this pin
map_MR [ pin_4_PWM_channel - 1 ] . PCR_bit = 0 ;
LPC_PINCON - > PINSEL3 & = ~ ( 0x3 < < 4 ) ; // return pin to general purpose I/O
map_MR [ pin_4_PWM_channel - 1 ] . PINSEL3_bits = 0 ;
map_MR [ pin_4_PWM_channel - 1 ] . map_PWM_INT = 0 ; // 0 - available for interrupts, 1 - in use by PWM
break ;
default :
break ;
void LPC1768_PWM_update ( void ) { // only called by the ISR
LPC1768_PWM_interrupt_mask = 0 ; // set match registers to new values, build IRQ mask
// first setup directly controlled PWM pin slots
bool found ;
for ( uint8_t i = 0 ; i < NUM_PWMS ; i + + ) {
ISR_table [ i ] . PCR_bit = 0 ; // clear entries
ISR_table [ i ] . PINSEL_reg = 0 ;
ISR_table [ i ] . PINSEL_bits = 0 ;
ISR_table [ i ] . PWM_flag = 1 ; // mark slot as interrupt mode until find differently
if ( ISR_table [ i ] . active_flag ) {
ISR_table [ i ] . sequence = i + 1 ;
// first see if there is a PWM1 controlled pin for this entry
found = false ;
for ( uint8_t j = 0 ; ( j < NUM_PWMS ) & & ! found ; j + + ) {
if ( ( map_MR [ j ] . map_PWM_PIN = = ISR_table [ i ] . pin ) ) {
map_MR [ j ] . map_PWM_INT = 1 ; // flag that it's already setup for direct control
ISR_table [ i ] . PWM_mask = 0 ;
ISR_table [ i ] . PCR_bit = map_MR [ j ] . PCR_bit ; // PCR register bit to enable PWM1 control of this pin
ISR_table [ i ] . PINSEL_reg = map_MR [ j ] . PINSEL_reg ; // PINSEL register address to set pin mode to PWM1 control} MR_map;
ISR_table [ i ] . PINSEL_bits = map_MR [ j ] . PINSEL_bits ; // PINSEL register bits to set pin mode to PWM1 control} MR_map;
map_MR [ j ] . map_used = 2 ;
ISR_table [ i ] . PWM_flag = 0 ;
* map_MR [ j ] . MR_register = ISR_table [ i ] . microseconds ;
found = true ;
}
}
}
else
ISR_table [ i ] . sequence = 0 ;
}
pinMode ( pin , INPUT ) ;
// next fill in interrupt slots
for ( uint8_t i = 0 ; i < NUM_PWMS ; i + + ) {
work_table [ slot ] = PWM_MAP_INIT_ROW ;
if ( ISR_table [ i ] . active_flag & & ISR_table [ i ] . PWM_flag ) {
LPC1768_PWM_update ( ) ;
// setup interrupt slot
found = false ;
for ( uint8_t k = 0 ; ( k < NUM_PWMS ) & & ! found ; k + + ) {
if ( ! ( map_MR [ k ] . map_PWM_INT | | map_MR [ k ] . map_used ) ) {
* map_MR [ k ] . MR_register = ISR_table [ i ] . microseconds ; // found one for an interrupt pin
map_MR [ k ] . map_used = 1 ;
LPC1768_PWM_interrupt_mask | = _BV ( 3 * ( k + 1 ) ) ; // set bit in the MCR to enable this MR to generate an interrupt
ISR_table [ i ] . set_register = PIN_IS_INVERTED ( ISR_table [ i ] . pin ) ? & LPC_GPIO ( LPC1768_PIN_PORT ( ISR_table [ i ] . pin ) ) - > FIOCLR : & LPC_GPIO ( LPC1768_PIN_PORT ( ISR_table [ i ] . pin ) ) - > FIOSET ;
ISR_table [ i ] . clr_register = PIN_IS_INVERTED ( ISR_table [ i ] . pin ) ? & LPC_GPIO ( LPC1768_PIN_PORT ( ISR_table [ i ] . pin ) ) - > FIOSET : & LPC_GPIO ( LPC1768_PIN_PORT ( ISR_table [ i ] . pin ) ) - > FIOCLR ;
ISR_table [ i ] . write_mask = LPC_PIN ( LPC1768_PIN_PIN ( ISR_table [ i ] . pin ) ) ;
ISR_table [ i ] . PWM_mask = _BV ( IR_BIT ( k + 1 ) ) ; // bit in the IR that will go active when this MR generates an interrupt
ISR_table [ i ] . PWM_flag = 1 ;
found = true ;
}
}
}
}
return 1 ;
LPC1768_PWM_interrupt_mask | = ( uint32_t ) _BV ( 0 ) ; // add in MR0 interrupt
LPC_PWM1 - > LER = 0x07E ; // Set the latch Enable Bits to load the new Match Values for MR1 - MR6
}
bool useable_hardware_PWM ( pin_t pin ) {
COPY_ACTIVE_TABLE ; // copy active table into work table
pin = GET_PIN_MAP_PIN ( GET_PIN_MAP_INDEX ( pin & 0xFF ) ) ;
NVIC_DisableIRQ ( PWM1_IRQn ) ;
bool return_flag = false ;
for ( uint8_t i = 0 ; i < NUM_PWMS ; i + + ) // see if it's already setup
if ( work_table [ i ] . pin = = pin & & work_table [ i ] . sequence ) return true ;
if ( ISR _table[ i ] . pin = = pin & & ISR _table[ i ] . sequence ) return_flag = true ;
for ( uint8_t i = 0 ; i < NUM_PWMS ; i + + ) // see if there is an empty slot
if ( ! work_table [ i ] . sequence ) return true ;
return false ; // only get here if neither the above are true
if ( ! ISR_table [ i ] . sequence ) return_flag = true ;
NVIC_EnableIRQ ( PWM1_IRQn ) ; // re-enable PWM interrupts
return return_flag ;
}
////////////////////////////////////////////////////////////////////////////////
# define HAL_PWM_LPC1768_ISR extern "C" void PWM1_IRQHandler(void)
// Both loops could be terminated when the last active channel is found but that would
// result in variations ISR run time which results in variations in pulse width
/**
* Changes to PINSEL3 , PCR and MCR are only done during the MR0 interrupt otherwise
* Changes to PINSEL , PCR and MCR are only done during the MR0 interrupt otherwise
* the wrong pin may be toggled or even have the system hang .
*/
HAL_PWM_LPC1768_ISR {
if ( PWM_table_swap ) ISR_table = work_table ; // use old table if a swap was just done
else ISR_table = active_table ;
if ( LPC_PWM1 - > IR & 0x1 ) { // MR0 interrupt
ISR_table = active_table ; // MR0 means new values could have been loaded so set everything
if ( PWM_table_swap ) LPC_PWM1 - > MCR = LPC1768_PWM_interrupt_mask ; // enable new PWM individual channel interrupts
if ( LPC_PWM1 - > IR & 0x1 ) { // MR0 interrupt
if ( ISR_table_update ) { // new values have been loaded so set everything
LPC1768_PWM_update ( ) ; // update & swap table
LPC_PWM1 - > MCR = LPC1768_PWM_interrupt_mask ; // enable new PWM individual channel interrupts
}
for ( uint8_t i = 0 ; i < NUM_PWMS ; i + + ) {
if ( ISR_table [ i ] . active_flag & & ! ( ( ISR_table [ i ] . pin = = P1_20 ) | |
( ISR_table [ i ] . pin = = P1_21 ) | |
( ISR_table [ i ] . pin = = P1_18 ) ) )
if ( ISR_table [ i ] . active_flag & & ! ( ( ISR_table [ i ] . pin = = P1_20 ) | |
( ISR_table [ i ] . pin = = P1_21 ) | |
( ISR_table [ i ] . pin = = P1_18 ) | |
( ISR_table [ i ] . pin = = P2_4 ) | |
( ISR_table [ i ] . pin = = P2_5 ) )
) {
* ISR_table [ i ] . set_register = ISR_table [ i ] . write_mask ; // set pins for all enabled interrupt channels active
if ( PWM_table_swap & & ISR_table [ i ] . PCR_bit ) {
LPC_PWM1 - > PCR | = ISR_table [ i ] . PCR_bit ; // enable PWM1 module control of this pin
LPC_PINCON - > PINSEL3 | = ISR_table [ i ] . PINSEL3_bits ; // set pin mode to PWM1 control - must be done after PCR
}
if ( ISR_table_update & & ISR_table [ i ] . PCR_bit ) {
LPC_PWM1 - > PCR | = ISR_table [ i ] . PCR_bit ; // enable PWM1 module control of this pin
* ISR_table [ i ] . PINSEL_reg | = ISR_table [ i ] . PINSEL_bits ; // set pin mode to PWM1 control - must be done after PCR
}
}
PWM_table_swap = false ;
PWM_MR0_wait = false ;
ISR_table_update = false ;
LPC_PWM1 - > IR = 0x01 ; // clear the MR0 interrupt flag bit
}
else {
for ( uint8_t i = 0 ; i < NUM_PWMS ; i + + )
if ( ISR_table [ i ] . active_flag & & ( LPC_PWM1 - > IR & ISR_table [ i ] . PWM_mask ) ) {
for ( uint8_t i = 0 ; i < NUM_PWMS ; i + + )
if ( ISR_table [ i ] . active_flag & & ( LPC_PWM1 - > IR & ISR_table [ i ] . PWM_mask ) ) {
LPC_PWM1 - > IR = ISR_table [ i ] . PWM_mask ; // clear the interrupt flag bits for expected interrupts
* ISR_table [ i ] . clr_register = ISR_table [ i ] . write_mask ; // set channel to inactive
}
}
LPC_PWM1 - > IR = 0x70F ; // guarantees all interrupt flags are cleared which, if there is an unexpected
// PWM interrupt, will keep the ISR from hanging which will crash the controller
return ;
// PWM interrupt, will keep the ISR from hanging which will crash the controller
}
# endif
/////////////////////////////////////////////////////////////////
@ -466,44 +502,26 @@ return;
* interrupt . The only exception is detaching pins . It doesn ' t matter when they go
* tristate .
*
* The LPC1768_PWM_init routine kicks off the MR0 interrupt . This interrupt is never disabled or
* delayed .
* The LPC1768_PWM_init routine kicks off the MR0 interrupt . This interrupt is never disabled . It
* can be delayed by higher priority interrupts . Actions on directly controlled pins are not delayed
* by other interrupts
*
* The PWM_table_swap flag is set when the firmware has swapped in an updated table . It is
* cleared by the ISR during the MR0 interrupt as it completes the swap and accompanying updates .
* It serves two purposes :
* 1 ) Tells the ISR that the tables have been swapped
* 2 ) Keeps the firmware from starting a new update until the previous one has been completed .
*
* The PWM_MR0_wait flag is set when the firmware is ready to swap in an updated table and cleared by
* the ISR during the MR0 interrupt . It is used to avoid delaying the MR0 interrupt when swapping in
* an updated table . This avoids glitches in pulse width and / or repetition rate .
* The ISR_table_update flag is set when the ISR table needs to be rebuilt . It is
* cleared by the ISR during the MR0 interrupt after it rebuilds the ISR table .
*
* The sequence of events during a write to a PWM channel is :
* 1 ) Waits until PWM_table_swap flag is false before starting
* 2 ) Copies the active table into the work table
* 3 ) Updates the work table
* NOTES - MR1 - MR6 are updated at this time . The updates aren ' t put into use until the first
* 1 ) Attach routine puts the pin number in the ISR table but doesn ' t mark it active .
* 2 ) Write routine marks the pin as active , updates the helper table and flags the ISR that the
* ISR table needs to be rebuilt .
* 3 ) On the MR0 interrupt the ISR :
* a . Rebuilds the ISR table if needed .
* MR1 - MR6 are updated at this time . The updates aren ' t put into use until the first
* MR0 after the LER register has been written . The LER register is written during the
* table swap process .
* - The MCR mask is created at this time . It is not used until the ISR writes the MCR
* during the MR0 interrupt in the table swap process .
* 4 ) Sets the PWM_MR0_wait flag
* 5 ) ISR clears the PWM_MR0_wait flag during the next MR0 interrupt
* 6 ) Once the PWM_MR0_wait flag is cleared then the firmware :
* disables the ISR interrupt
* swaps the pointers to the tables
* writes to the LER register
* sets the PWM_table_swap flag active
* re - enables the ISR
* 7 ) On the next interrupt the ISR changes its pointer to the work table which is now the old ,
* unmodified , active table .
* 8 ) On the next MR0 interrupt the ISR :
* switches over to the active table
* clears the PWM_table_swap and PWM_MR0_wait flags
* updates the MCR register with the possibly new interrupt sources / assignments
* writes to the PCR register to enable the direct control of the Servo 0 , 1 & 3 pins by the PWM1 module
* sets the PINSEL3 register to function / mode 0x2 for the Servo 0 , 1 & 3 pins
* NOTE - PCR must be set before PINSEL
* sets the pins controlled by the ISR to their active states
* table rebuild process . The result is new timing takes 20 - 40 mS to be implemented .
* b . Sets the interrupt controlled pin ( s ) to their active state
* c . Writes to the PCR register to enable the directly controlled pins
* d . Sets the PINSEL register to the function / mode for the directly controlled pins
*
* 4 ) For each interrupt controlled pin there is another ISR call . During this call the pin is set
* to its inactive state . The call is initiated when a MR1 - MR6 reg times out .
*/