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This commit is contained in:
Scott Lahteine 2018-05-27 00:10:05 -05:00
parent 1b200f3312
commit 2566342979
1 changed files with 20 additions and 21 deletions
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23
Marlin/src/module/stepper.cpp
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@ -320,8 +320,8 @@ void Stepper::set_directions() {
#if ENABLED(S_CURVE_ACCELERATION) #if ENABLED(S_CURVE_ACCELERATION)
/** /**
* We are using a quintic (fifth-degree) Bézier polynomial for the velocity curve. * This uses a quintic (fifth-degree) Bézier polynomial for the velocity curve, giving
* This gives us a "linear pop" velocity curve; with pop being the sixth derivative of position: * a "linear pop" velocity curve; with pop being the sixth derivative of position:
* velocity - 1st, acceleration - 2nd, jerk - 3rd, snap - 4th, crackle - 5th, pop - 6th * velocity - 1st, acceleration - 2nd, jerk - 3rd, snap - 4th, crackle - 5th, pop - 6th
* *
* The Bézier curve takes the form: * The Bézier curve takes the form:
@ -395,7 +395,7 @@ void Stepper::set_directions() {
* *
* For Any 32bit CPU: * For Any 32bit CPU:
* *
* At the start of each trapezoid, we calculate the coefficients A,B,C,F and Advance [AV], as follows: * At the start of each trapezoid, calculate the coefficients A,B,C,F and Advance [AV], as follows:
* *
* A = 6*128*(VF - VI) = 768*(VF - VI) * A = 6*128*(VF - VI) = 768*(VF - VI)
* B = 15*128*(VI - VF) = 1920*(VI - VF) * B = 15*128*(VI - VF) = 1920*(VI - VF)
@ -403,7 +403,7 @@ void Stepper::set_directions() {
* F = 128*VI = 128*VI * F = 128*VI = 128*VI
* AV = (1<<32)/TS ~= 0xFFFFFFFF / TS (To use ARM UDIV, that is 32 bits) (this is computed at the planner, to offload expensive calculations from the ISR) * AV = (1<<32)/TS ~= 0xFFFFFFFF / TS (To use ARM UDIV, that is 32 bits) (this is computed at the planner, to offload expensive calculations from the ISR)
* *
* And for each point, we will evaluate the curve with the following sequence: * And for each point, evaluate the curve with the following sequence:
* *
* void lsrs(uint32_t& d, uint32_t s, int cnt) { * void lsrs(uint32_t& d, uint32_t s, int cnt) {
* d = s >> cnt; * d = s >> cnt;
@ -456,10 +456,10 @@ void Stepper::set_directions() {
* return alo; * return alo;
* } * }
* *
* This will be rewritten in ARM assembly to get peak performance and will take 43 cycles to execute * This is rewritten in ARM assembly for optimal performance (43 cycles to execute).
* *
* For AVR, we scale precision of coefficients to make it possible to evaluate the Bézier curve in * For AVR, the precision of coefficients is scaled so the Bézier curve can be evaluated in real-time:
* realtime: Let's reduce precision as much as possible. After some experimentation we found that: * Let's reduce precision as much as possible. After some experimentation we found that:
* *
* Assume t and AV with 24 bits is enough * Assume t and AV with 24 bits is enough
* A = 6*(VF - VI) * A = 6*(VF - VI)
@ -480,7 +480,7 @@ void Stepper::set_directions() {
* C: signed Q24 , range = 250000 *10 = 2500000 = 0x1312D0 | 21 bits * C: signed Q24 , range = 250000 *10 = 2500000 = 0x1312D0 | 21 bits
* F: signed Q24 , range = 250000 = 250000 = 0x0ED090 | 20 bits * F: signed Q24 , range = 250000 = 250000 = 0x0ED090 | 20 bits
* *
* And for each curve, we estimate its coefficients with: * And for each curve, estimate its coefficients with:
* *
* void _calc_bezier_curve_coeffs(int32_t v0, int32_t v1, uint32_t av) { * void _calc_bezier_curve_coeffs(int32_t v0, int32_t v1, uint32_t av) {
* // Calculate the Bézier coefficients * // Calculate the Bézier coefficients
@ -499,7 +499,7 @@ void Stepper::set_directions() {
* bezier_F = v0; * bezier_F = v0;
* } * }
* *
* And for each point, we will evaluate the curve with the following sequence: * And for each point, evaluate the curve with the following sequence:
* *
* // unsigned multiplication of 24 bits x 24bits, return upper 16 bits * // unsigned multiplication of 24 bits x 24bits, return upper 16 bits
* void umul24x24to16hi(uint16_t& r, uint24_t op1, uint24_t op2) { * void umul24x24to16hi(uint16_t& r, uint24_t op1, uint24_t op2) {
@ -549,9 +549,8 @@ void Stepper::set_directions() {
* } * }
* return acc; * return acc;
* } * }
* Those functions will be translated into assembler to get peak performance. coefficient calculations takes 70 cycles, * These functions are translated to assembler for optimal performance.
* Bezier point evaluation takes 150 cycles * Coefficient calculation takes 70 cycles. Bezier point evaluation takes 150 cycles.
*
*/ */
#ifdef __AVR__ #ifdef __AVR__