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79 lines
3.2 KiB
79 lines
3.2 KiB
/**
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* Marlin 3D Printer Firmware
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* Copyright (C) 2017 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
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*
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* Based on Sprinter and grbl.
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* Copyright (C) 2011 Camiel Gubbels / Erik van der Zalm
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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/**
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* The class Servo uses the PWM class to implement its functions
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*
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* All PWMs use the same repetition rate - 20mS because that's the normal servo rate
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*/
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/**
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* This is a hybrid system.
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*
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* The PWM1 module is used to directly control the Servo 0, 1 & 3 pins. This keeps
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* the pulse width jitter to under a microsecond.
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*
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* For all other pins the PWM1 module is used to generate interrupts. The ISR
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* routine does the actual setting/clearing of pins. The upside is that any pin can
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* have a PWM channel assigned to it. The downside is that there is more pulse width
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* jitter. The jitter depends on what else is happening in the system and what ISRs
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* prempt the PWM ISR. Writing to the SD card can add 20 microseconds to the pulse
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* width.
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*/
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/**
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* The data structures are setup to minimize the computation done by the ISR which
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* minimizes ISR execution time. Execution times are 2.2 - 3.7 microseconds.
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*
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* Two tables are used. active_table is used by the ISR. Changes to the table are
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* are done by copying the active_table into the work_table, updating the work_table
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* and then swapping the two tables. Swapping is done by manipulating pointers.
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*
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* Immediately after the swap the ISR uses the work_table until the start of the
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* next 20mS cycle. During this transition the "work_table" is actually the table
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* that was being used before the swap. The "active_table" contains the data that
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* will start being used at the start of the next 20mS period. This keeps the pins
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* well behaved during the transition.
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*
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* The ISR's priority is set to the maximum otherwise other ISRs can cause considerable
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* jitter in the PWM high time.
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*
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* See the end of this file for details on the hardware/firmware interaction
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*/
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#ifndef _LPC1768_PWM_H_
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#define _LPC1768_PWM_H_
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#include <pinmapping.h>
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#include <lpc17xx_clkpwr.h>
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#define LPC_PWM1_MR0 19999 // base repetition rate minus one count - 20mS
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#define LPC_PWM1_PCLKSEL0 CLKPWR_PCLKSEL_CCLK_DIV_4 // select clock divider for prescaler - defaults to 4 on power up
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#define MR0_MARGIN 200 // if channel value too close to MR0 the system locks up
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void LPC1768_PWM_init(void);
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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);
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bool LPC1768_PWM_write(pin_t pin, uint32_t value);
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bool LPC1768_PWM_detach_pin(pin_t pin);
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bool useable_hardware_PWM(pin_t pin);
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#endif // _LPC1768_PWM_H_
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