[ion] Encode the serial number in Base64

Also, expose serialNumber() in Ion and keep "copySerialNumber" in
Ion::Device. This allows the DFU bootloader to remain .bss-free.

apps/hardware_test/serial_number_controller.cpp

@@ -10,9 +10,7 @@ SerialNumberController::SerialNumberController(Responder * parentResponder) :
 }
 
 void SerialNumberController::viewWillAppear() {
-  static char serialNumber[24];
-  Ion::getSerialNumber(serialNumber);
-  m_barCodeView.setData(serialNumber);
+  m_barCodeView.setData(Ion::serialNumber());
 }
 
 bool SerialNumberController::handleEvent(Ion::Events::Event event) {

apps/settings/sub_controller.cpp

@@ -192,24 +192,13 @@ void SubController::willDisplayCellForIndex(HighlightCell * cell, int index) {
   }
   if (m_messageTreeModel->label() == I18n::Message::About) {
     myCell->setMessageFontSize(KDText::FontSize::Small);
-    const char * accessoryMessage = nullptr;
-    char serialNumber[Ion::SerialNumberLength+1];
-    switch (index) {
-      case 0:
-        accessoryMessage = Ion::softwareVersion();
-        break;
-      case 1:
-        Ion::getSerialNumber(serialNumber);
-        accessoryMessage = serialNumber;
-        break;
-      case 2:
-        accessoryMessage = Ion::fccId();
-        break;
-      default:
-        assert(false);
-        break;
-    }
-    myCell->setAccessoryText(accessoryMessage);
+    const char * messages[] = {
+      Ion::softwareVersion(),
+      Ion::serialNumber(),
+      Ion::fccId()
+    };
+    assert(index >= 0 && index < 3);
+    myCell->setAccessoryText(messages[index]);
   }
 }
 

ion/include/ion.h

@@ -28,8 +28,7 @@ namespace Ion {
 void msleep(long ms);
 void usleep(long us);
 
-constexpr static int SerialNumberLength = 24;
-void getSerialNumber(char * buffer);
+const char * serialNumber();
 const char * softwareVersion();
 const char * patchLevel();
 const char * fccId();

ion/src/device/Makefile

@@ -15,6 +15,7 @@ objs += $(addprefix ion/src/shared/, \
 objs += $(addprefix ion/src/device/, \
   backlight.o \
   battery.o\
+  base64.o\
   console.o \
   device.o\
   display.o\

ion/src/device/base64.cpp

@@ -0,0 +1,48 @@
+namespace Base64 {
+
+static constexpr char encodeTable[] = {
+  'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
+  'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
+  'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
+  'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
+  'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
+  'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
+  'w', 'x', 'y', 'z', '0', '1', '2', '3',
+  '4', '5', '6', '7', '8', '9', '+', '/',
+};
+
+constexpr char Padding = '=';
+
+void encode(const unsigned char * input, unsigned int inputLength, char * output) {
+  unsigned int i, j;
+  for (i = j = 0; i < inputLength; i++) {
+    int s = i % 3; /* from 6/gcd(6, 8) */
+
+    switch (s) {
+      case 0:
+        output[j++] = encodeTable[(input[i] >> 2) & 0x3F];
+        continue;
+      case 1:
+        output[j++] = encodeTable[((input[i-1] & 0x3) << 4) + ((input[i] >> 4) & 0xF)];
+        continue;
+      case 2:
+        output[j++] = encodeTable[((input[i-1] & 0xF) << 2) + ((input[i] >> 6) & 0x3)];
+        output[j++] = encodeTable[input[i] & 0x3F];
+    }
+  }
+
+  /* move back */
+  i -= 1;
+
+  /* check the last and add padding */
+  if ((i % 3) == 0) {
+    output[j++] = encodeTable[(input[i] & 0x3) << 4];
+    output[j++] = Padding;
+    output[j++] = Padding;
+  } else if ((i % 3) == 1) {
+    output[j++] = encodeTable[(input[i] & 0xF) << 2];
+    output[j++] = Padding;
+  }
+}
+
+}

ion/src/device/base64.h

@@ -0,0 +1,5 @@
+namespace Base64 {
+
+void encode(const unsigned char * input, unsigned int inputLength, char * output);
+
+}

ion/src/device/bench/command/mcu_serial.cpp

@@ -1,5 +1,6 @@
 #include "command.h"
 #include <ion.h>
+#include "../../device.h"
 
 namespace Ion {
 namespace Device {
@@ -11,8 +12,8 @@ void MCUSerial(const char * input) {
     reply(sSyntaxError);
     return;
   }
-  char response[11+Ion::SerialNumberLength + 1] = {'M', 'C', 'U', '_', 'S', 'E', 'R', 'I', 'A', 'L', '=', 0};
-  Ion::getSerialNumber(response+11);
+  char response[11 + Ion::Device::SerialNumberLength + 1] = {'M', 'C', 'U', '_', 'S', 'E', 'R', 'I', 'A', 'L', '=', 0};
+  Ion::Device::copySerialNumber(response + 11);
   reply(response);
 }
 

ion/src/device/device.cpp

@@ -14,6 +14,7 @@ extern "C" {
 #include "swd.h"
 #include "usb.h"
 #include "bench/bench.h"
+#include "base64.h"
 
 #define USE_SD_CARD 0
 
@@ -65,23 +66,18 @@ uint32_t Ion::random() {
   return result;
 }
 
-
-
-static inline char hex(uint8_t d) {
-  if (d > 9) {
-    return 'A'+d-10;
-  }
-  return '0'+d;
+void Ion::Device::copySerialNumber(char * buffer) {
+  const unsigned char * rawUniqueID = (const unsigned char *)0x1FFF7A10;
+  Base64::encode(rawUniqueID, 12, buffer);
+  buffer[SerialNumberLength] = 0;
 }
 
-void Ion::getSerialNumber(char * buffer) {
-  uint8_t * rawUniqueID = (uint8_t *)0x1FFF7A10;
-  for (int i=0; i<SerialNumberLength/2; i++) {
-    uint8_t d = *rawUniqueID++;
-    buffer[2*i] = hex(d >> 4);
-    buffer[2*i+1] = hex(d & 0xF);
+const char * Ion::serialNumber() {
+  static char serialNumber[Device::SerialNumberLength + 1] = {0};
+  if (serialNumber[0] == 0) {
+    Device::copySerialNumber(serialNumber);
   }
-  buffer[SerialNumberLength] = 0;
+  return serialNumber;
 }
 
 // Private Ion::Device methods

ion/src/device/device.h

@@ -16,6 +16,14 @@ void shutdownPeripherals();
 void initClocks();
 void shutdownClocks();
 
+/* The serial number is 96 bits long. That's equal to 16 digits in base 64. We
+ * expose a convenient "copySerialNumber" routine which can be called without
+ * using a static variable (and therefore without a .bss section). This is used
+ * in the RAM'ed DFU bootloader. */
+constexpr static int SerialNumberLength = 16;
+void copySerialNumber(char * buffer);
+
+
 /*  Pin | Role              | Mode                  | Function
  * -----+-------------------+-----------------------+----------
  *  PA0 | Battery sensing   |                       |

ion/src/device/usb/Makefile

@@ -45,6 +45,7 @@ dfu_objs += ion/src/device/usb/boot.o
 dfu_objs += ion/src/device/keyboard.o
 dfu_objs += ion/src/device/device.o
 dfu_objs += ion/src/device/usb.o
+dfu_objs += ion/src/device/base64.o
 
 ion/src/device/usb/dfu.elf: LDFLAGS = --gc-sections -T ion/src/device/usb/dfu.ld
 ion/src/device/usb/dfu.elf: $(usb_objs) $(dfu_objs)

ion/src/device/usb/calculator.cpp

@@ -9,8 +9,8 @@ namespace USB {
 namespace Device {
 
 void Calculator::PollAndReset(bool exitWithKeyboard) {
-  char serialNumber[Ion::SerialNumberLength+1];
-  Ion::getSerialNumber(serialNumber);
+  char serialNumber[Ion::Device::SerialNumberLength+1];
+  Ion::Device::copySerialNumber(serialNumber);
   Calculator c(serialNumber);
 
   /* Leave DFU mode if the Back key is pressed, the calculator unplugged or the

ion/src/shared/dummy/serial_number.cpp

@@ -1,5 +1,5 @@
 #include <ion.h>
 
-void Ion::getSerialNumber(char * buffer) {
-  strlcpy(buffer, "000000000000000000000000", Ion::SerialNumberLength+1);
+const char * Ion::serialNumber() {
+  return "000000000000";
 }

ion/src/simulator/Makefile

@@ -17,6 +17,7 @@ objs += $(addprefix ion/src/shared/, \
   dummy/backlight.o \
   dummy/battery.o \
   dummy/fcc_id.o \
+  dummy/serial_number.o \
   dummy/usb.o \
 )
 

ion/src/simulator/init.cpp

@@ -116,7 +116,3 @@ void Ion::msleep(long ms) {
     }
   }
 }
-
-void Ion::getSerialNumber(char * buffer) {
-  strlcpy(buffer, "Simulator", Ion::SerialNumberLength+1);
-}