From efb781bed5999b25164fbf6e65050d169881b8eb Mon Sep 17 00:00:00 2001
From: Wurstnase <wurstnase.reprap@gmail.com>
Date: Fri, 20 May 2016 08:22:33 +0200
Subject: [PATCH] Temp: faster cycles in continuous mode.

Thermistors and AD595 can be faster in that mode.

The new stategy is:

  1. read the value
  2. start the adc
  3. return the result
  - next cycle

instead of:

  1. start the adc
  - wait 10ms
  2. read the value
  3. return the result
  - next cycle

Review changes by Traumflug: fixed the warnings appearing in some
configurations (case NEEDS_START_ADC undefined and case
NEEDS_START_ADC defined, but TEMP_READ_CONTINUOUS == 0)
---
 temp.c | 37 +++++++++++++++++++++++++++++++------
 1 file changed, 31 insertions(+), 6 deletions(-)

diff --git a/temp.c b/temp.c
index 4f7a9bf..f957a70 100644
--- a/temp.c
+++ b/temp.c
@@ -268,17 +268,31 @@ static uint16_t temp_read_max6675(temp_sensor_t i) {
 
 #ifdef TEMP_THERMISTOR
 static uint16_t temp_read_thermistor(temp_sensor_t i) {
+  // Needs to be 'static', else GCC diagnostics emits a warning "'result' may
+  // be used uninitialized". No surprise about this warning, it's part of the
+  // logic that in some configurations temp_sensors_runtime[i].active never
+  // reaches more than 1.
+  static uint16_t result;
+
   switch (temp_sensors_runtime[i].active++) {
     case 1:  // Start ADC conversion.
       #ifdef NEEDS_START_ADC
+        #if TEMP_READ_CONTINUOUS
+          result = analog_read(i);
+        #endif
         start_adc();
-        return TEMP_NOT_READY;
+        #if ! TEMP_READ_CONTINUOUS
+          return TEMP_NOT_READY;
+        #endif
       #endif
-      // else fall through to conversion
+      // If not in continuous mode or no need for start_adc() fall through.
 
     case 2:  // Convert temperature values.
+      #if ! defined NEEDS_START_ADC || ! TEMP_READ_CONTINUOUS
+        result = analog_read(i);
+      #endif
       temp_sensors_runtime[i].active = 0;
-      return temp_table_lookup(analog_read(i), i);
+      return temp_table_lookup(result, i);
   }
   return TEMP_NOT_READY;
 }
@@ -326,19 +340,30 @@ static uint16_t temp_read_mcp3008(temp_sensor_t i) {
 
 #ifdef TEMP_AD595
 static uint16_t temp_read_ad595(temp_sensor_t i) {
+  // Needs to be 'static', see comment in temp_read_thermistor().
+  static uint16_t result;
+
   switch (temp_sensors_runtime[i].active++) {
     case 1:  // Start ADC conversion.
       #ifdef NEEDS_START_ADC
+        #if TEMP_READ_CONTINUOUS
+          result = analog_read(i);
+        #endif
         start_adc();
-        return TEMP_NOT_READY;
+        #if ! TEMP_READ_CONTINUOUS
+          return TEMP_NOT_READY;
+        #endif
       #endif
-      // else fall through to conversion
+      // If not in continuous mode or no need for start_adc() fall through.
 
     case 2:  // Convert temperature values.
+      #if ! TEMP_READ_CONTINUOUS
+        result = analog_read(i);
+      #endif
       temp_sensors_runtime[i].active = 0;
       // Convert >> 8 instead of >> 10 because internal temp is stored as
       // 14.2 fixed point.
-      return (analog_read(i) * 500L) >> 8;
+      return (result * 500L) >> 8;
   }
   return TEMP_NOT_READY;
 }