Save lots of PROGMEM, ~20b SRAM with DIGIPOT_I2C

Marlin/Marlin_main.cpp

 #endif // !SDSUPPORT
 
 #if ENABLED(DIGIPOT_I2C)
-  extern void digipot_i2c_set_current(int channel, float current);
+  extern void digipot_i2c_set_current(uint8_t channel, float current);
   extern void digipot_i2c_init();
 #endif
 

Marlin/SanityCheck.h

 #endif
 
 /**
+ * Digipot requirement
+ */
+#if ENABLED(DIGIPOT_MCP4018)
+  #if !defined(DIGIPOTS_I2C_SDA_X) || !defined(DIGIPOTS_I2C_SDA_Y) || !defined(DIGIPOTS_I2C_SDA_Z) \
+    || !defined(DIGIPOTS_I2C_SDA_E0) || !defined(DIGIPOTS_I2C_SDA_E1)
+      #error "DIGIPOT_MCP4018 requires DIGIPOTS_I2C_SDA_* pins to be defined."
+  #endif
+#endif
+
+/**
  * Require 4 or more elements in per-axis initializers
  */
 constexpr float sanity_arr_1[] = DEFAULT_AXIS_STEPS_PER_UNIT,

Marlin/digipot_mcp4018.cpp

 
 #if ENABLED(DIGIPOT_I2C) && ENABLED(DIGIPOT_MCP4018)
 
+#include "enum.h"
 #include "Stream.h"
 #include "utility/twi.h"
 #include <SlowSoftI2CMaster.h>  //https://github.com/stawel/SlowSoftI2CMaster
 
 #define DIGIPOT_A4988_Itripmax(Vref)    ((Vref)/(8.0*DIGIPOT_A4988_Rsx))
 
-#define DIGIPOT_A4988_FACTOR            (DIGIPOT_A4988_MAX_VALUE/DIGIPOT_A4988_Itripmax(DIGIPOT_A4988_Vrefmax))
+#define DIGIPOT_A4988_FACTOR            ((DIGIPOT_A4988_MAX_VALUE)/DIGIPOT_A4988_Itripmax(DIGIPOT_A4988_Vrefmax))
 //TODO: MAX_CURRENT -0.5A ?? (currently set to 2A, max possible current 2.5A)
 #define DIGIPOT_A4988_MAX_CURRENT       (DIGIPOT_A4988_Itripmax(DIGIPOT_A4988_Vrefmax) - 0.5)
 
-static byte current_to_wiper(float current) {
-  return byte(ceil(float((DIGIPOT_A4988_FACTOR * current))));
+static byte current_to_wiper(const float current) {
+  return byte(ceil(float(DIGIPOT_A4988_FACTOR) * current));
 }
 
-static uint8_t sda_pins[DIGIPOT_I2C_NUM_CHANNELS] = {
-  DIGIPOTS_I2C_SDA_X,
-  DIGIPOTS_I2C_SDA_Y,
-  DIGIPOTS_I2C_SDA_Z,
-  DIGIPOTS_I2C_SDA_E0,
-  DIGIPOTS_I2C_SDA_E1,
+const uint8_t sda_pins[DIGIPOT_I2C_NUM_CHANNELS] = {
+  DIGIPOTS_I2C_SDA_X
+  #if DIGIPOT_I2C_NUM_CHANNELS > 1
+    , DIGIPOTS_I2C_SDA_Y
+    #if DIGIPOT_I2C_NUM_CHANNELS > 2
+      , DIGIPOTS_I2C_SDA_Z
+      #if DIGIPOT_I2C_NUM_CHANNELS > 3
+        , DIGIPOTS_I2C_SDA_E0
+        #if DIGIPOT_I2C_NUM_CHANNELS > 4
+          , DIGIPOTS_I2C_SDA_E1
+        #endif
+      #endif
+    #endif
+  #endif
 };
 
 static SlowSoftI2CMaster pots[DIGIPOT_I2C_NUM_CHANNELS] = {
-  SlowSoftI2CMaster { sda_pins[0], DIGIPOTS_I2C_SCL },
-  SlowSoftI2CMaster { sda_pins[1], DIGIPOTS_I2C_SCL },
-  SlowSoftI2CMaster { sda_pins[2], DIGIPOTS_I2C_SCL },
-  SlowSoftI2CMaster { sda_pins[3], DIGIPOTS_I2C_SCL },
-  SlowSoftI2CMaster { sda_pins[4], DIGIPOTS_I2C_SCL }
+  SlowSoftI2CMaster { sda_pins[X_AXIS], DIGIPOTS_I2C_SCL }
+  #if DIGIPOT_I2C_NUM_CHANNELS > 1
+    , SlowSoftI2CMaster { sda_pins[Y_AXIS], DIGIPOTS_I2C_SCL }
+    #if DIGIPOT_I2C_NUM_CHANNELS > 2
+      , SlowSoftI2CMaster { sda_pins[Z_AXIS], DIGIPOTS_I2C_SCL }
+      #if DIGIPOT_I2C_NUM_CHANNELS > 3
+        , SlowSoftI2CMaster { sda_pins[E_AXIS], DIGIPOTS_I2C_SCL }
+        #if DIGIPOT_I2C_NUM_CHANNELS > 4
+          , SlowSoftI2CMaster { sda_pins[E_AXIS + 1], DIGIPOTS_I2C_SCL }
+        #endif
+      #endif
+    #endif
+  #endif
 };
 
-static void i2c_send(int channel, byte v) {
+static void i2c_send(const uint8_t channel, const byte v) {
   if (WITHIN(channel, 0, DIGIPOT_I2C_NUM_CHANNELS - 1)) {
     pots[channel].i2c_start(((DIGIPOT_I2C_ADDRESS) << 1) | I2C_WRITE);
     pots[channel].i2c_write(v);
 }
 
 // This is for the MCP4018 I2C based digipot
-void digipot_i2c_set_current(int channel, float current) {
-  current = min(max(current, 0.0f), float(DIGIPOT_A4988_MAX_CURRENT));
-
-  i2c_send(channel, current_to_wiper(current));
+void digipot_i2c_set_current(uint8_t channel, float current) {
+  i2c_send(channel, current_to_wiper(min(max(current, 0.0f), float(DIGIPOT_A4988_MAX_CURRENT))));
 }
 
 void digipot_i2c_init() {
-  const float digipot_motor_current[] = DIGIPOT_I2C_MOTOR_CURRENTS;
+  static const float digipot_motor_current[] PROGMEM = DIGIPOT_I2C_MOTOR_CURRENTS;
 
   for (uint8_t i = 0; i < DIGIPOT_I2C_NUM_CHANNELS; i++)
     pots[i].i2c_init();
 
   // setup initial currents as defined in Configuration_adv.h
   for (uint8_t i = 0; i < COUNT(digipot_motor_current); i++)
-    digipot_i2c_set_current(i, digipot_motor_current[i]);
+    digipot_i2c_set_current(i, pgm_read_float(&digipot_motor_current[i]));
 }
 
 #endif // DIGIPOT_I2C && DIGIPOT_MCP4018

Marlin/digipot_mcp4451.cpp

   #define DIGIPOT_I2C_MAX_CURRENT 2.5
 #endif
 
-static byte current_to_wiper(float current) {
+static byte current_to_wiper(const float current) {
   return byte(ceil(float((DIGIPOT_I2C_FACTOR * current))));
 }
 
-static void i2c_send(byte addr, byte a, byte b) {
+static void i2c_send(const byte addr, const byte a, const byte b) {
   Wire.beginTransmission(addr);
   Wire.write(a);
   Wire.write(b);
 }
 
 // This is for the MCP4451 I2C based digipot
-void digipot_i2c_set_current(int channel, float current) {
+void digipot_i2c_set_current(uint8_t channel, float current) {
   current = min((float) max(current, 0.0f), DIGIPOT_I2C_MAX_CURRENT);
   // these addresses are specific to Azteeg X3 Pro, can be set to others,
   // In this case first digipot is at address A0=0, A1= 0, second one is at A0=0, A1= 1
 }
 
 void digipot_i2c_init() {
-  const float digipot_motor_current[] = DIGIPOT_I2C_MOTOR_CURRENTS;
+  static const float digipot_motor_current[] PROGMEM = DIGIPOT_I2C_MOTOR_CURRENTS;
   Wire.begin();
   // setup initial currents as defined in Configuration_adv.h
-  for (int i = 0; i < COUNT(digipot_motor_current); i++)
-    digipot_i2c_set_current(i, digipot_motor_current[i]);
+  for (uint8_t i = 0; i < COUNT(digipot_motor_current); i++)
+    digipot_i2c_set_current(i, pgm_read_float(&digipot_motor_current[i]));
 }
 
 #endif // DIGIPOT_I2C