modify:

1. elite init setting add: adc_gain use GAIN_3P000
2. [test] adc read AIN2 only
3. ads8691 read twice

ads8691.c

@@ -249,6 +249,8 @@ static int ads8691_read(uint32_t channel, int32_t *adc_val)
         nrf_delay_us(100);
     }
 
+    read_word();
+
     uint32_t val = read_word();
     *adc_val     = val >> 14;
 

edc20.c

@@ -919,6 +919,7 @@ elite_instance_t edc20_elite_instance = {
 
 static void init(void)
 {
+    adc_gain(GAIN_3P000);
     circuit_selection_dac_fune_tune_f2();
 }
 

edc20_pin_ctrl.c

@@ -591,7 +591,7 @@ void TIMER3_IRQHandler(void)
 
         float mv;
         extern int adc_read_milivolt(uint32_t channel, float *mv);
-        adc_read_milivolt(7, &mv);
+        adc_read_milivolt(2, &mv);
 
         float v = mv / 1000.0;
         extern void j_scope_update(float f);