Yet Another Virtual Oscilloscope for Arduino

1/*
2 * ADC sampling decimation factor. Only one of each DECIMATION_FACTOR
3  * samples will be written to the buffer. Increase this value if you
4 * are having  problems with communication reliability.
5 * 
6 * The sampling frequency (in  Hz) will be:
7 * 
8 *   Fs = 16000000 (CPU clock frequency) / 128 (ADC prescaler)  /
9 *        13 (cycles per conversion) / DECIMATION_FACTOR
10 */
11
12#define  DECIMATION_FACTOR 2
13
14/* 
15 * A circular buffer to store up to 256 ADC samples.  Indexes are of
16 * "byte" type to make buffer overrun impossible.
17 */
18
19volatile  unsigned int adcBuffer[256];
20volatile byte adcWriteIndex=0;
21byte adcReadIndex=0;
22volatile  bool triggered=false;
23
24/* Digital pin states */
25
26byte pinState[14];
27byte  pinPWM[14];
28
29/* Synchronization settings */
30
31volatile byte syncMode=0;  /* 0 - off, 1 - rising edge, 2 - falling edge */
32volatile byte syncSource=0;  /* 0 - analog input, >0 - digital pin */
33volatile unsigned int syncLevel=512;  /* signal level for the oscilloscope to trigger */
34byte syncOffset=128; /* how  many samples before the trigger event will be displayed */
35
36/* Packet size  setting */
37
38unsigned int packetSize=512;
39
40void setup() {
41/* 
42  * Configure the ADC 
43 * ADMUX:  REFS=01 (use AVCC for reference), MUX=0000 (use  ADC0 input)
44 * ADCSRB: ADTS=000 (free running mode, the new conversion will be  started
45 *         immediately after the previous one has been completed)
46  * ADCSRA: ADEN=1 (enable ADC), ADSC=1 (start conversion),
47 *         ADATE=1  (enable auto trigger), ADIE=1 (enable ADC interrupt),
48 *         ADPS=111 (set  ADC prescaler to 128)
49 */
50  ADMUX=0x40;
51  ADCSRB=0;
52  ADCSRA=0xEF;
53  Serial.begin(115200);
54}
55
56void loop() {
57/* Buffer for incoming data,  can hold up to 3 bytes */
58  static byte cmdBuffer[3];
59  static byte cmdBytes=0;
60
61  if(Serial.available()) {
62/* Process incoming data */
63    byte ch=Serial.read();
64    if(cmdBytes==0) {
65/* Look for a start of a packet */
66      if(ch==0x50||ch==0x51)  {
67        cmdBuffer[0]=ch;
68        cmdBytes++;
69      }
70    }
71    else  {
72/* Packet continuation */
73      cmdBuffer[cmdBytes]=ch;
74      cmdBytes++;
75    }
76    
77    if(cmdBuffer[0]==0x50&&cmdBytes==3) {
78/* Write register  */
79      writeVirtualRegister(cmdBuffer[1],cmdBuffer[2]);
80      cmdBytes=0;
81    }
82    else if(cmdBuffer[0]==0x51&&cmdBytes==2) {
83/* Read register */
84      byte data=readVirtualRegister(cmdBuffer[1]);
85      byte buf[2];
86      buf[0]=0x80|(data>>4);  /* upper 4 bits */
87      buf[1]=data&0x0F; /* lower 4 bits */
88      Serial.write(buf,2);
89      cmdBytes=0;
90    }
91  }
92  else if(adcWriteIndex!=adcReadIndex) {
93/*  No incoming data, transmit data from the ADC circular buffer if present */
94    static  unsigned int sampleCnt=0;
95    byte queue=adcWriteIndex-adcReadIndex;
96    if(sampleCnt==0&&syncMode!=0)  { /* start of packet, wait for trigger */
97      if(queue<syncOffset) {
98        triggered=false;
99        return;
100      }
101      if(!triggered) {
102        if(queue>syncOffset)  adcReadIndex++;
103        return;
104      }
105    }
106    unsigned int data=adcBuffer[adcReadIndex++];
107    byte buf[2];
108    buf[0]=0xC0|(data>>5); /* upper 5 bits */
109    if(sampleCnt==0)  buf[0]|=0x20; /* start of packet mark */
110    buf[1]=data&0x1F; /* lower 5 bits  */
111    Serial.write(buf,2);
112    if(++sampleCnt>=packetSize) sampleCnt=0;
113    triggered=false;
114  }
115}
116
117void writeVirtualRegister(byte addr,byte  data) {
118/* ADC input channel */
119  if(addr==0) ADMUX=(ADMUX&0xF0)|(data&0x0F);
120/*  ADC reference voltage */
121  else if(addr==1) ADMUX=(ADMUX&0x3F)|(data<<6);
122/*  Pin mode registers */
123  else if(addr>=2&&addr<=13) {
124    pinState[addr]=data;
125    setPinState(addr);
126  }
127/* PWM value registers */
128  else if(addr>=18&&addr<=29)  {
129    pinPWM[addr-16]=data;
130    setPinState(addr-16);
131  }
132/* Synchronization  settings and packet size */
133  else if(addr==32) syncMode=data;
134  else if(addr==33)  syncSource=data;
135  else if(addr==34) syncLevel=static_cast<unsigned int>(data)<<2;
136  else if(addr==35) syncOffset=data;
137  else if(addr==36) reinterpret_cast<byte*>(&packetSize)[0]=data;
138  else if(addr==37) reinterpret_cast<byte*>(&packetSize)[1]=data;
139}
140
141byte  readVirtualRegister(byte addr) {
142  if(addr==0) return ADMUX&0x0F;
143  else if(addr==1)  return ADMUX>>6;
144  else if(addr>=2&&addr<=13) return pinState[addr];
145  else  if(addr>=18&&addr<=29) return pinPWM[addr-16];
146  else if(addr==32) return syncMode;
147  else if(addr==33) return syncSource;
148  else if(addr==34) return static_cast<byte>(syncLevel>>2);
149  else if(addr==35) return syncOffset;
150  else if(addr==36) return reinterpret_cast<byte*>(&packetSize)[0];
151  else if(addr==37) return reinterpret_cast<byte*>(&packetSize)[1];
152  return  0;
153}
154
155void setPinState(byte pin) {
156  switch(pinState[pin]) {
157  case  0: /* input */
158    pinMode(pin,INPUT);
159    break;
160  case 1: /* input_pullup  */
161    pinMode(pin,INPUT_PULLUP);
162    break;
163  case 2: /* force low */
164    pinMode(pin,OUTPUT);
165    digitalWrite(pin,LOW);
166    break;
167  case 3:  /* force high */
168    pinMode(pin,OUTPUT);
169    digitalWrite(pin,HIGH);
170    break;
171  case 4: /* PWM */
172    analogWrite(pin,pinPWM[pin]);
173    break;
174  }
175}
176
177/* Process the ADC interrupt */
178
179ISR(ADC_vect) {
180  static  byte cnt=0;
181  static unsigned int old_sample=0;
182  if(++cnt==DECIMATION_FACTOR)  cnt=0;
183  if(cnt==0) {
184    unsigned int sample=ADCL|(ADCH<<8);
185/* Check  trigger conditions */
186    if(syncSource==0) { /* trigger by the analog input  */
187      if(syncMode==1&&sample>=syncLevel&&old_sample<syncLevel) triggered=true;
188      else if(syncMode==2&&sample<=syncLevel&&old_sample>syncLevel) triggered=true;
189      old_sample=sample;
190    }
191    else { /* trigger by a digital input */
192      unsigned int s=digitalRead(syncSource);
193      if(syncMode==1&&s==HIGH&&old_sample==LOW)  triggered=true;
194      else if(syncMode==2&&s==LOW&&old_sample==HIGH) triggered=true;
195      old_sample=s;
196    }
197    adcBuffer[adcWriteIndex++]=sample;
198  }
199}
200