Diff: main.cpp

Revision:

4:0b3b70b0af0b

Parent:

3:bfb6d1e6deee

Child:

6:f005cc78b9aa

--- a/main.cpp	Thu Oct 23 00:19:42 2014 +0000
+++ b/main.cpp	Thu Oct 30 02:56:50 2014 +0000
@@ -2,7 +2,7 @@
 // FIR フィルタ，基本的な構造, 固定小数点演算用 DSP 命令を使う
 //      Analog Input : A0
 //      Analog Output: MCP4922 using SPI
-// 2014/10/23, Copyright (c) 2014 MIKAMI, Naoki
+// 2014/10/29, Copyright (c) 2014 MIKAMI, Naoki
 //--------------------------------------------------------------
 
 #include "mbed.h"
@@ -15,6 +15,7 @@
 using namespace Mikami;
 
 const int FS_ = 12000;  // Sampling frequency: 12 kHz
+const uint16_t OFFSET = 2047;   // Correspond to "0"
 ADC_Base adc_(A0, FS_); // for AD
 DAC_MCP4922 myDac_;     // for DA
 
@@ -28,7 +29,7 @@
     
     while (true)
     {
-        xn[0] = adc_.Read_u16() - 2047;     // Read from A0
+        xn[0] = adc_.Read_u16() - OFFSET;     // Read from A0
         //-----------------------------------------------
 
         int32_t yn = hm_[ORDER_]*xn[ORDER_];;
@@ -41,8 +42,9 @@
         for (int k=ORDER_; k>0; k--)
             xn[k] = xn[k-1];        // move input signals
 
-        yn = (yn + 0x8000) >> 15;   // rounding and devide by 32768
+        // rounding and devide by 32768 + DC offset
+        uint16_t yOut = ((yn + 0x8000) >> 15) + OFFSET;
         //-----------------------------------------------
-        myDac_.Write((uint16_t)(yn + 2047));    // Write to DAC
+        myDac_.Write(yOut);         // Write to DAC
     }
 }