From 2403b07ec0a7586108798271fa04eb034445f51d Mon Sep 17 00:00:00 2001
From: bnewbold <bnewbold@robocracy.org>
Date: Mon, 24 Dec 2012 15:39:35 +0100
Subject: updates to documentation, code cleanup, comments

---
 bytetunes.cpp | 249 +++++++++++++++++++++++++++++++---------------------------
 1 file changed, 132 insertions(+), 117 deletions(-)

(limited to 'bytetunes.cpp')

diff --git a/bytetunes.cpp b/bytetunes.cpp
index 470d51f..ce9f557 100644
--- a/bytetunes.cpp
+++ b/bytetunes.cpp
@@ -1,13 +1,28 @@
+/*
+ * bytebeat.cpp - parse and play bytebeat songs
+ * Date: December 2012
+ * Author: bnewbold@robocracy.org
+ *
+ * For use with libmaple, to run on ARM Cortex-M3 microcontrollers.
+ *
+ * This version only parses tunes in "perfect" S-EXPR format.
+ *
+ * Outputs PWM audio on pin 16 and listens on SerialUSB for new tunes.
+ *
+ * See TODO file for problems.
+ *
+ * This file is released under the General Public License version 3 (GPLv3).
+ */
 
 #include "wirish.h"
-//#include <stdio.h>
 #include <string.h>
-//#include <stdlib.h>
 
-#define DEFAULT "(& (>> t 6) (& (* 2 t) (>> t 1)))"
-#define NUMNODE 160
-#define PWM_OUT_PIN     33
+#define DEFAULT_TUNE    "(& (>> t 6) (& (* 2 t) (>> t 1)))"
+#define NUMNODE         160
+#define LED_PIN         33
+#define MONITOR_PIN     31
 
+// S-EXPR data structure stuff
 struct node {
     char type;
     char cval;
@@ -15,73 +30,59 @@ struct node {
     struct node *lval;
     struct node *rval;
 };
+struct node *new_node(char type, char cval, unsigned int ival,
+                      struct node *lval, struct node *rval);
+static struct node active_table[NUMNODE];
+static struct node node_table[NUMNODE];
+static int newest_node = 0;
 
+// S-EXPR parser stuff
 int isdigit(char);
 void print_sexpr(struct node *sexpr);
-int execute(struct node *sexpr, unsigned int t);
 int find_split(char* s, int start, int end);
 struct node *parse(char *s, int start, int end);
-struct node *new_node(char type, char cval, unsigned int ival,
-                      struct node *lval, struct node *rval);
+int digtoi(char *s, int start, int end);
 
-static struct node active_table[NUMNODE];
-static struct node node_table[NUMNODE];
-static int newest_node = 0;
+// bytetune machine output stuff
+int execute(struct node *sexpr, unsigned int t);
 node *machine;
 node *new_machine;
 void handler_sample(void);
-
-unsigned char sin_8bit(int counter, int period);
-char inbuffer[256];
-
-int sstrlen(char *s, int max);
-
 HardwareTimer gen(1);
 HardwareTimer pwm(4);
-
 int counter = 0;
 
-int isdigit(char c) {
-    return (c >= '0' and c <= '9');
-}
+// other stuff
+char inbuffer[256];
+int inbuffer_index;
+int sstrlen(char *s, int max);
 
-/*
-from math import sin
-count = 64
-print [int(127+127*sin(3.14159268*2*i/count)) for i in range(count)]
-*/
-unsigned char sine_lookup[] __FLASH__ = {127, 139, 151, 163, 175, 186, 197, 207, 216,
-    225, 232, 239, 244, 248, 251, 253, 254, 253, 251, 248, 244, 239, 232, 225,
-    216, 207, 197, 186, 175, 163, 151, 139, 126, 114, 102, 90, 78, 67, 56, 46,
-    37, 28, 21, 14, 9, 5, 2, 0, 0, 0, 2, 5, 9, 14, 21, 28, 37, 46, 56, 67, 78,
-    90, 102, 114};
+// ====================== primary control flow functions ======================
 
+// runs once at power up to configure hardware peripherals
 void setup() {
     int i;
-    pinMode(PWM_OUT_PIN, OUTPUT);
-    pinMode(31, OUTPUT);
-    pinMode(33, OUTPUT);
-    pinMode(16, PWM);
-    pinMode(4, OUTPUT);
-    digitalWrite(1, 1);
-
-    // initialize with DEFAULT machines
-    machine = parse((char*)DEFAULT, 0, strlen((char*)DEFAULT)-1);
+
+    // for monitoring interrupt loop length
+    pinMode(LED_PIN, OUTPUT);
+    pinMode(MONITOR_PIN, OUTPUT);
+
+    // initialize with DEFAULT_TUNE
+    machine = parse((char*)DEFAULT_TUNE, 0, strlen((char*)DEFAULT_TUNE)-1);
     for (i=0;i<NUMNODE;i++) {
         active_table[i] = node_table[i];
     }
 
-    // configure PWM output
-    pinMode(PWM_OUT_PIN, OUTPUT);
+    // configure PWM output on pin 16 (Timer 4, Channel 1)
+    pinMode(16, PWM);               // primary PWM audio output
     pwm.setMode(1, TIMER_PWM);
     pwm.setPrescaleFactor(1);
-    pwm.setOverflow(255);       // 8-bit resolution
-    pwm.setCompare(3, 128);        // initialize to "zero"
-
+    pwm.setOverflow(255);           // 8-bit resolution
+    pwm.setCompare(3, 128);         // initialize to "zero"
 
     // configure 8KHz ticker and interrupt handler
     gen.pause();
-    gen.setPeriod(125);         // 8Khz
+    gen.setPeriod(125);             // 8Khz
     gen.setCompare(1, 1);
     gen.setMode(1, TIMER_OUTPUT_COMPARE);
     gen.attachInterrupt(1, handler_sample);
@@ -91,32 +92,34 @@ void setup() {
     gen.resume();
 }
 
-int inbuffer_index;
-
+// runs continuously, reading new machines from SerialUSB input
 void loop() {
     int len, i;
+
     SerialUSB.println();
     SerialUSB.println("Currently playing:");
     print_sexpr(machine);
     SerialUSB.println();
     SerialUSB.println("Input a tune in exact s-expr syntax:");
     SerialUSB.print("> ");
+
     inbuffer_index = 0;
     while (1) {
+        // read in characters one at a time
         inbuffer[inbuffer_index] = SerialUSB.read();
+        if (inbuffer[inbuffer_index] > 127) {
+            // if not an ASCII character ignore it
+            continue;
+        }
         SerialUSB.print(inbuffer[inbuffer_index]);
-        if (inbuffer[inbuffer_index] == 8) {
-            if (inbuffer_index > 0) {
-                inbuffer_index--;
-            }
-        } else if (inbuffer[inbuffer_index] == '\n' ||
+        if (inbuffer[inbuffer_index] == '\n' ||
                    inbuffer[inbuffer_index] == '\r') {
+            // on submit, zero terminate the string and break out to parse
             inbuffer[inbuffer_index] = '\0';
             SerialUSB.println();
             break;
-        } else {
-            inbuffer_index++;
         }
+        inbuffer_index++;
         if (inbuffer_index == 256) {
             SerialUSB.println("\n\rInput too long!");
             return;
@@ -124,15 +127,17 @@ void loop() {
     }
     len = sstrlen(inbuffer, 256);
     if (len == 256 || len < 1) {
+        // too long or short
         SerialUSB.println("Invalid input!");
         return;
     }
+    // ok, we're going to try parsing
     newest_node = 0;
     new_machine = parse(inbuffer, 0, len-2);
     if (new_machine == NULL) {
         return;
     }
-    // swap in new machine
+    // if we got this far, swap in the new machine
     gen.pause();
     for (i=0;i<NUMNODE;i++) {
         active_table[i] = node_table[i];
@@ -146,55 +151,32 @@ void loop() {
     gen.resume();
 }
 
+// gets called by 8KHz timer interrupt. pushes out the next audio sample to PWM
+// output
 void handler_sample(void) {
-    digitalWrite(33, 1);
-    digitalWrite(31, 1);
-    //pwm.setCompare(1, sin_8bit(counter, 799));  // 10Hz sine wave
+    // set LED and monitor line high (so we can check with a 'scope how long
+    // this function call lasts)
+    digitalWrite(LED_PIN, 1);
+    digitalWrite(MONITOR_PIN, 1);
+
+    // execute and write truncated result
     pwm.setCompare(1, (0x000000FF & execute(machine, counter)));
-    //pwmWrite(16, sin_8bit(counter, 800));
     counter++;
-    //SerialUSB.print('.');
-    digitalWrite(33, 0);
-    digitalWrite(31, 0);
-}
 
-unsigned char sin_8bit(int counter, int period) {
-    int high, low;
-    float t = (counter % period) / (float)period;
-    float weight = t - (int)t;
-    low = sine_lookup[(int)(63*t)];
-    if (63*t > 62)
-        //high = sine_lookup[0];
-        high = 118;
-    else
-        high = sine_lookup[1+(int)(63*t)];
-
-    return (int)(high * weight + low * (1.0 - weight));
+    // set LED and monitor line low
+    digitalWrite(LED_PIN, 0);
+    digitalWrite(MONITOR_PIN, 0);
 }
 
-int sstrlen(char *s, int max) {
-    int i;
-    for (i=0; i<max; i++) {
-        if (s[i] == '\n' || s[i] == '\0') {
-            return i+1;
-        }
-    }
-    return max;
+int main(void) {
+    setup();
+    while (true) { loop(); }
+    return 0;
 }
 
-int digtoi(char *s, int start, int end) {
-    int num = 0;
-    for(;start<=end;start++) {
-        if (! isdigit(s[start])) {
-            SerialUSB.print("parse: not a digit: ");
-            SerialUSB.println(s[start]);
-            return -1;
-        }
-        num = num*10 + (s[start] - '0');
-    }
-    return num;
-}
+// ====================== tune parsing and playback functions =================
 
+// does what it says; returns NULL if there is a problem
 struct node *parse(char *s, int start, int end) {
     struct node *lval, *rval;
     char cval;
@@ -251,6 +233,10 @@ struct node *parse(char *s, int start, int end) {
     return NULL;
 }
 
+// calculates a single audio sample (index 't') from tune 'sexpr'.
+// returns an int, which should be truncated to 8bit length for playback
+// if there is a problem, tries to print out to SerialUSB and returns "zero"
+// value
 int execute(struct node *sexpr, unsigned int t) {
     switch (sexpr->type) {
     // atom
@@ -265,6 +251,7 @@ int execute(struct node *sexpr, unsigned int t) {
         } else {
             SerialUSB.print("unexpected unary oper: ");
             SerialUSB.println(sexpr->cval);
+            return 127;
         }
     // binary
     case 'b':
@@ -292,17 +279,18 @@ int execute(struct node *sexpr, unsigned int t) {
         default:
             SerialUSB.print("unexpected binary oper: ");
             SerialUSB.print(sexpr->cval);
-            return NULL;
-            // XXX: halt
+            return 127;
         }
     default:
         SerialUSB.print("execute: unknown type: ");
         SerialUSB.print(sexpr->type);
-        return NULL;
-        // XXX: halt
+        return 127;
     }
 }
 
+// finds the seperating whitespace character between the two arguments to a
+// binary S-EXPR operator
+// returns either the index of the seperator or -1 if there was a problem
 int find_split(char *s, int start, int end) {
     int depth = 0;
     int i;
@@ -316,19 +304,17 @@ int find_split(char *s, int start, int end) {
         if (depth < 0) {
             SerialUSB.print("parse: unmatched ')'\n");
             return -1;
-            // XXX: fail
         }
     }
     if (depth > 0) {
         SerialUSB.print("parse: unmatched '('\n");
         return -1;
-        // XXX: fail
     }
     SerialUSB.print("parse: could not find split\n");
     return -1;
-    // XXX: fail
 }
 
+// prints out the S-EXPR to SerialUSB
 void print_sexpr(struct node *sexpr) {
     char oper = '_';
     char twice = 0;
@@ -347,7 +333,8 @@ void print_sexpr(struct node *sexpr) {
             print_sexpr(sexpr->rval);
             SerialUSB.print(")");
         } else {
-            SerialUSB.print("unexpected unary: ");
+            SerialUSB.println();
+            SerialUSB.print("print_sexpr: unexpected unary: ");
             SerialUSB.println(sexpr->cval);
         }
     // binary operators
@@ -371,21 +358,24 @@ void print_sexpr(struct node *sexpr) {
             print_sexpr(sexpr->rval);
             SerialUSB.print(')');
         } else {
-            SerialUSB.print("unexpected binary: ");
+            SerialUSB.println();
+            SerialUSB.print("print_sexpr: unexpected binary: ");
             SerialUSB.println(sexpr->cval);
-            // XXX:
+            return;
         }
 
     }
 }
 
+// creates a new node struct in the node table
 struct node *new_node(char type, char cval, unsigned int ival, 
                       struct node *lval, struct node *rval) {
     struct node *n;
     newest_node++;
     if (newest_node >= NUMNODE) {
-        SerialUSB.print("node table overrun\n");
-        // XXX:
+        SerialUSB.println();
+        SerialUSB.println("node table overrun!");
+        return NULL;
     }
     n = &node_table[newest_node];
     n->type = type;
@@ -396,18 +386,43 @@ struct node *new_node(char type, char cval, unsigned int ival,
     return n;
 }
 
+// ====================== misc helper functions ======================
+
+// "safe" string length. breaks on newline or NULL char, checks at most 'max'
+// characters
+int sstrlen(char *s, int max) {
+    int i;
+    for (i=0; i<max; i++) {
+        if (s[i] == '\n' || s[i] == '\0') {
+            return i+1;
+        }
+    }
+    return max;
+}
+
+// finds a (positive) integer.
+// returns -1 if there is a problem.
+int digtoi(char *s, int start, int end) {
+    int num = 0;
+    for(;start<=end;start++) {
+        if (! isdigit(s[start])) {
+            SerialUSB.print("parse: not a digit: ");
+            SerialUSB.println(s[start]);
+            return -1;
+        }
+        num = num*10 + (s[start] - '0');
+    }
+    return num;
+}
+
+int isdigit(char c) {
+    return (c >= '0' and c <= '9');
+}
+
+// libmaple-specific re-definition
 // Force init to be called *first*, i.e. before static object allocation.
 // Otherwise, statically allocated objects that need libmaple may fail.
 __attribute__((constructor)) void premain() {
     init();
 }
 
-int main(void) {
-    setup();
-
-    while (true) {
-        loop();
-    }
-
-    return 0;
-}
-- 
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