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315 lines
17 KiB
NASM
315 lines
17 KiB
NASM
;throttle_momentum.asm
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.NOLIST
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; ***************************************************************************************
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; * PWM MODEL RAILROAD THROTTLE *
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; * *
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; * WRITTEN BY: PHILIP DEVRIES *
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; * *
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; * Copyright (C) 2003 Philip DeVries *
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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 2 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, write to the Free Software *
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; * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA *
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; * *
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; ***************************************************************************************:
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.LIST
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.ifdef MOMENTUM_ENABLED
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;********************************************************************************
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;* MOMENTUM_ADJUST *
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;* Top level routine *
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;* *
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;* Momentum simulates the mass of the train. Since model trains have little *
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;* mass, the locomotive speed can directly follow the throttle setting; in *
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;* other words, a model train can accelerate and decelerate instantly. *
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;* Real trains are very massive, and therefore they do not accelerate or *
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;* decelerate quickly. *
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;* *
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;* According to Newtons law, the acceleration is proportional to the force, *
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;* and inversely proportional to the mass. Therefore, the more massive the *
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;* train, the more slowly the train will accelerate or decelerate. Also, the *
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;* more force the locomotive can provide, the faster the train will accelerate. *
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;* Deceler depends on the braking capability of the overall train. *
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;* *
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;* If force were constant, Newtons law states that acceleration would be *
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;* constant too. This subroutine assumes that somewhat more force is *
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;* available at low speeds than at high speeds, so that acceleration will be *
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;* greater at low speeds. The subroutine also assumes that opposing forces *
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;* (friction, wind resistance, etc) are stronger at higher speeds. This *
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;* assumption also means that acceleration will be greater at low speeds. *
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;* *
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;* This subroutine calculates acceleration/deceleration by this simple *
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;* Method: *
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;* *
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;* The rate of speed change (accleration and deceleration) depends on the *
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;* current speed as *
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;* {Speed_Max (0xFF) - Current_Speed} / {Tau*Rate} *
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;* *
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;* Where T = index of sample time *
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;* t = real time *
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;* Tau = time constant *
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;* Rate = Update rate (nominally 100Hz) *
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;* *
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;* That is, the acceleration/deceleration is maximum at zero speed, and *
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;* approaches zero at maximum speed. *
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;* *
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;* When accelerating, the speed at the next sample period is *
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;* Speed(T) = Speed(T-1) + {0xFF - Speed(T-1)} / {Tau*Rate} *
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;* *
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;* Giving an acceleration curve that looks like a normal exponential. *
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;* Speed(t) = 0xFF { 1 - exp( - t / Tau) } *
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;* *
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;* * * *
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;* * *
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;* * *
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;* * *
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;* * *
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;* * *
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;* * *
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;* * *
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;* *
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;* *
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;* When decelerating, the change rate equation is the same, but the change *
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;* is subtracted, as *
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;* Speed(T) = Speed(T) - {0xFF - Speed(T-1)} / {Tau*Rate} *
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;* *
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;* Giving a deceleration curve that looks like *
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;* Speed(t) = 0xFF { 1 - exp( -(T1 - t) / Tau) } *
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;* which is a mirror image of the acceleration, NOT a normal exponential. *
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;* *
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;* * * *
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;* * *
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;* * *
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;* * *
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;* * *
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;* * *
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;* * *
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;* *
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;* *
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;* In each case, the acceleration or deceleration is "clipped" at the current *
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;* throttle setting so that the speed doesn't overshoot or undershoot. *
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;* *
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;* Three different values of Tau are used, that is *
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;* Tau_accel Corresponding to acceleration under power *
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;* Tau_coast Corresponding to deceleration when coasting *
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;* Tau_brake Corresponding to deceleration when braking *
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;* *
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;* To permit finer control of momentum, the throttle setting is converted to a *
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;* 16 bit number, where the 8 msb's correspond to the throttle setting from *
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;* the throttle handle and sent forward. *
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;* *
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;* Inputs: throttle_set Throttle handle position ( 0x00 to 0xFF ) *
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;* speed_hi_prev Hi byte of (T-1) throttle setting (stored) *
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;* speed_lo_prev Lo byte of (T-1) throttle setting (stored) *
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;* Returns: throttle_set Adjusted throttle setting (T) *
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;* speed_hi_prev Hi byte of (T) throttle setting (stored) *
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;* speed_lo_prev Lo byte of (T) throttle setting (stored) *
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;* Changed: B_Temp *
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;* B_Temp1 *
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;* B_Temp2 *
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;* B_Temp3 *
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;* Calls: NONE *
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;* Goto: MOMENTUM_ADJUST_RETURN *
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;********************************************************************************
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B_TEMPLOCAL2 _time_constant_adj
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.ifdef TRADITIONAL_ENABLED
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.ifdef LEDS_ENABLED
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sbrc Flags_1,BF_brake ; If the brake flag is set,
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sbi PORTB,dir_in_port ; Port Output: Indicate deceleration
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.endif ;LEDS_ENABLED
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.endif ;TRADITIONAL_ENABLED
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;*******************************************************************
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;* Adjust the value of "momentum_set".
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;* This adjustment makes it easier to fine adjust low momentum settings
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;* while still permitting large momentum settings.
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;*
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;* The ammount of momentum to apply comes in in "momentum_set"
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;* which is read in READ_THROTTLE. The nominal range is
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;* 0x00 to 0x40. This value is multiplied by two and squared,
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;* giving a new range from 0x00 to 0x4000. The update rate is 100Hz,
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;* and so the new range corresponds to a time constant from
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;* 0(decimal) to 164(decimal) seconds. Since the adjustment was
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;* done by performing a square, the adjusted value is non-linear
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;* with the input value.
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;*******************************************************************
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lsl momentum_set ; multiply by two
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HILOCAL1 _mset_multiplier ; supply to mpy8u
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B_TEMPLOCAL _mset_multiplicand ; supply to mpy8u
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mov _mset_multiplier,momentum_set ;
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mov _mset_multiplicand,momentum_set ;
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rcall mpy8u ; square
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B_TEMPLOCAL1 _mset_hi_byte ; return from mpy8u
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B_TEMPLOCAL _mset_lo_byte ; return from mpy8u
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;*******************************************************************
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;* Compute the difference between the maximum throttle and
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;* the current throttle
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;*******************************************************************
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HILOCAL2 _mset_diff_hi_byte
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HILOCAL1 _mset_diff_lo_byte
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ldi _mset_diff_hi_byte,0xFF ; Maximum possible speed
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ldi _mset_diff_lo_byte,0xFF ;
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sub _mset_diff_lo_byte,speed_lo_prev ; Difference between max speed
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sbc _mset_diff_hi_byte,speed_hi_prev ; and current speed
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;*******************************************************************
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;* Determine whether to accelerate, decelerate, or remain unchanged.
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;* Compare the throttle handle setting with the actual speed
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;*******************************************************************
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cp throttle_set,speed_hi_prev ; Test if throttle position is larger
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; or smaller than the speed.
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breq EVEN_SPEED ; If the throttle position is the same
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; as the speed.
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brlo SETUP_DECELERATE ; If the throttle position is smaller
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; than the speed, then need to decelerate.
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; brsh SETUP_ACCELERATE ; If the throttle position is larger
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; than the speed, then need to accelerate.
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SETUP_ACCELERATE:
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.ifdef TRADITIONAL_ENABLED
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.ifdef LEDS_ENABLED
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cpi throttle_set,accel_led_threshold ; If the throttle is less than minimum
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brlo END_SET_ACCEL_LED ; don't light led
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mov B_Temp2,throttle_set ; If the throttle is closer than led_threshold
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subi B_Temp2,accel_led_threshold ; don't light led
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cp B_Temp2,speed_hi_prev
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brlo END_SET_ACCEL_LED
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sbi PORTB,momentum_port ; Port Output: Indicate acceleration
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END_SET_ACCEL_LED:
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.endif LEDS_ENABLED
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.endif TRADITIONAL_ENABLED
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sbr Flags_1,F_accel ; Set accelerating flag
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; Indicate acceleration
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ldi _time_constant_adj,accel_offset+1 ; Acceleration time constant adjust
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rjmp CHECK_BRAKE
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EVEN_SPEED: ; Arrive here if throttle_set=current speed
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sbrc Flags_1,BF_brake ; If the brake flag is set, decelerate
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rjmp CHECK_BRAKE ;
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rjmp DONE_WITH_MOMENTUM ; Otherwise adjustment is necessary
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SETUP_DECELERATE:
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cbr Flags_1,F_accel ; Clear accelerating flag
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.ifdef TRADITIONAL_ENABLED
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.ifdef LEDS_ENABLED
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cpi throttle_set,0xff-decel_led_threshold ; If the throttle is more than maximum
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brsh END_SET_DECEL_LED ; don't light led
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mov B_Temp2,throttle_set
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subi B_Temp2,0x00-decel_led_threshold ; If the throttle is closer than the led
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cp B_Temp2,speed_hi_prev ; threshold, don't light the led
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brsh END_SET_DECEL_LED
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sbi PORTB,dir_in_port ; Port Output: Indicate deceleration
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END_SET_DECEL_LED:
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.endif LEDS_ENABLED
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.endif TRADITIONAL_ENABLED
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ldi _time_constant_adj,0+1 ; Coasting deceleration time const. adjust.
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; rjmp CHECK_BRAKE
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CHECK_BRAKE: ; Always check for the brake.
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sbrs Flags_1,BF_brake ; If brake flag is not set,
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rjmp ADJUST_TAU ; proceed.
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; Brake overrides acceleration
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; or coasting.
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cbr Flags_1,F_accel ; clear accelerating flag
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; Indicate deceleration
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ldi _time_constant_adj,brake_offset+1 ; Braking deceleration time const. adjust.
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; rjmp ADJUST_TAU
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ADJUST_TAU:
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;B_TEMP2=B_TEMPLOCAL2
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dec _time_constant_adj ; Divide tau_base by 2^_time_constant_adj
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breq DIVIDE_TAU ; to produce adjusted tau.
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lsr _mset_hi_byte
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ror _mset_lo_byte
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rjmp ADJUST_TAU
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DIVIDE_TAU:
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sbr _mset_lo_byte,0b00000001 ; Force last bit 1. Prevent divide by zero.
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rcall div16u ; Divide _mset_diff_hi_byte:_mset_diff_lo_byte
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; (difference)
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; by _mset_hi_byte:_mset_lo_byte (dividor)
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sbrs Flags_1,BF_accel ; add or subtract change depending
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rjmp SUBTRACT_CHANGE ; on F_accel flag
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;rjmp ADD_CHANGE
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ADD_CHANGE: ; Case accelerating
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; HILOCAL2 _mset_diff_hi_byte
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; HILOCAL1 _mset_diff_lo_byte
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add speed_lo_prev,_mset_diff_lo_byte ; Add in the change
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adc speed_hi_prev,_mset_diff_hi_byte
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cp throttle_set,speed_hi_prev ; If larger than the throttle_set value
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brlo USE_SET_SPEED ; clamp at throttle_set value
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rjmp DONE_WITH_MOMENTUM
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SUBTRACT_CHANGE: ; Case decelerating
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sbrc Flags_1,BF_brake ; If the brake flag is set,
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clr throttle_set ; decelerate all the way to zero
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sub speed_lo_prev,_mset_diff_lo_byte ; Subtract the change
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sbc speed_hi_prev,_mset_diff_hi_byte ;
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brlo USE_SET_SPEED ; If less than zero
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; clamp at throttle_set value
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cp speed_hi_prev,throttle_set ; If less than the throttle_set value
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brlo USE_SET_SPEED ; clamp at throttle_set value
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rjmp DONE_WITH_MOMENTUM
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USE_SET_SPEED: ; Use the throttle_set value directly
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mov speed_hi_prev,throttle_set
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clr speed_lo_prev
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DONE_WITH_MOMENTUM:
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mov throttle_set,speed_hi_prev ; Put the new value into throttle_set.
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.endif ;MOMENTUM_ENABLED
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