diff --git a/.travis.yml b/.travis.yml
index 8c61b8aa..011e4ddc 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,4 @@
-dist: xenial
+dist: bionic
 language: c
 compiler: gcc
 addons:
@@ -8,13 +8,14 @@ addons:
     packages:
       - gcc-8
       - cppcheck
+      - python3-venv
+      - wget
 services:
   - docker
 before_install:
-    - sudo add-apt-repository -y ppa:team-gcc-arm-embedded/ppa
-    - sudo apt-get update -q
-    - sudo apt-get install -y gcc-arm-embedded python3-venv
+  - wget -O gcc-arm.tar.bz2 'https://developer.arm.com/-/media/Files/downloads/gnu-rm/9-2019q4/RC2.1/gcc-arm-none-eabi-9-2019-q4-major-x86_64-linux.tar.bz2?revision=6e63531f-8cb1-40b9-bbfc-8a57cdfc01b4&la=en&hash=F761343D43A0587E8AC0925B723C04DBFB848339'
+  - sudo tar -jxf gcc-arm.tar.bz2 --strip-components=1 -C /
+  - rm gcc-arm.tar.bz2
 script:
   - export CC=gcc-8
-  - pyenv shell 3.6.7
   - make travis
diff --git a/Makefile b/Makefile
index 9259be73..d903bd37 100644
--- a/Makefile
+++ b/Makefile
@@ -68,7 +68,7 @@ venv:
 	python3 -m venv venv
 	venv/bin/pip -q install --upgrade pip
 	venv/bin/pip -q install --upgrade -r tools/requirements.txt
-	venv/bin/pip -q install --upgrade black
+	venv/bin/pip -q install --upgrade black==19.3b0 # Versions newer than this require regex, which fails to compile
 
 # selectively reformat our own code
 black: venv
@@ -110,7 +110,8 @@ CPPCHECK_FLAGS=--quiet --error-exitcode=2
 cppcheck:
 	cppcheck $(CPPCHECK_FLAGS) crypto/aes-gcm
 	cppcheck $(CPPCHECK_FLAGS) crypto/sha256
-	cppcheck $(CPPCHECK_FLAGS) fido2
+	cppcheck $(CPPCHECK_FLAGS) fido2 -DAPP_CONFIG=app.h
+	cppcheck $(CPPCHECK_FLAGS) fido2 -DAPP_CONFIG=bootloader.h
 	cppcheck $(CPPCHECK_FLAGS) pc
 
 clean:
@@ -135,4 +136,4 @@ test-docker:
 travis:
 	$(MAKE) test VENV=". ../../venv/bin/activate;"
 	$(MAKE) test-docker
-	$(MAKE) black
\ No newline at end of file
+	$(MAKE) black
diff --git a/targets/stm32l432/build/bootloader.mk b/targets/stm32l432/build/bootloader.mk
index db7aff25..896c6526 100644
--- a/targets/stm32l432/build/bootloader.mk
+++ b/targets/stm32l432/build/bootloader.mk
@@ -3,9 +3,13 @@ include build/common.mk
 # ST related
 SRC = bootloader/main.c bootloader/bootloader.c
 SRC += bootloader/pubkey_bootloader.c bootloader/version_check.c
-SRC += src/init.c src/redirect.c src/flash.c src/rng.c src/led.c src/device.c
 SRC += src/fifo.c src/attestation.c src/sense.c
 SRC += src/startup_stm32l432xx.s src/system_stm32l4xx.c
+# Important: device.c must come after startup_stm32l432xx.s to work around
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83967. If the order is switched,
+# compilation will succeed but the output will be missing overridden weak
+# symbols.
+SRC += src/init.c src/redirect.c src/flash.c src/rng.c src/led.c src/device.c
 SRC += $(DRIVER_LIBS) $(USB_LIB)
 
 # FIDO2 lib
@@ -34,6 +38,11 @@ CFLAGS= $(INC)
 
 TARGET=bootloader
 HW=-mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard -mthumb
+ifeq (${DEBUG},1)
+	LTO_FLAG=
+else
+	LTO_FLAG=-flto
+endif
 
 # Solo or Nucleo board
 CHIP=STM32L432xx
@@ -45,8 +54,8 @@ endif
 DEFINES = -DDEBUG_LEVEL=$(DEBUG) -D$(CHIP) -DAES256=1  -DUSE_FULL_LL_DRIVER -DAPP_CONFIG=\"bootloader.h\" $(EXTRA_DEFINES)
 # DEFINES += -DTEST_SOLO_STM32 -DTEST -DTEST_FIFO=1
 
-CFLAGS=$(INC) -c $(DEFINES)   -Wall -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -fdata-sections -ffunction-sections $(HW) -g $(VERSION_FLAGS)
-LDFLAGS_LIB=$(HW) $(SEARCH) -specs=nano.specs  -specs=nosys.specs  -Wl,--gc-sections  -lnosys
+CFLAGS=$(INC) -c $(DEFINES)   -Wall -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -fdata-sections -ffunction-sections $(HW) -g $(VERSION_FLAGS) ${LTO_FLAG}
+LDFLAGS_LIB=$(HW) $(SEARCH) -specs=nano.specs  -specs=nosys.specs  -Wl,--gc-sections  -lnosys ${LTO_FLAG}
 LDFLAGS=$(HW) $(LDFLAGS_LIB) -T$(LDSCRIPT) -Wl,-Map=$(TARGET).map,--cref  -Wl,-Bstatic
 
 
diff --git a/targets/stm32l432/src/device.c b/targets/stm32l432/src/device.c
index 1a83ebc5..eb0caf7a 100644
--- a/targets/stm32l432/src/device.c
+++ b/targets/stm32l432/src/device.c
@@ -290,10 +290,7 @@ void device_init()
 
     hw_init(LOW_FREQUENCY);
 
-    if (! tsc_sensor_exists())
-    {
-        _NFC_status = nfc_init();
-    }
+     _NFC_status = nfc_init();
 
     if (_NFC_status == NFC_IS_ACTIVE)
     {
diff --git a/targets/stm32l432/src/sense.c b/targets/stm32l432/src/sense.c
index 37a16561..f38e123a 100644
--- a/targets/stm32l432/src/sense.c
+++ b/targets/stm32l432/src/sense.c
@@ -5,8 +5,20 @@
 #include "stm32l4xx_ll_gpio.h"
 #include "stm32l4xx_hal_tsc.h"
 
-#define ELECTRODE_0     TSC_GROUP2_IO1
-#define ELECTRODE_1     TSC_GROUP2_IO2
+/**
+USB A Nano & USB C Touch TSC GPIO Configuration:
+PB4   ------> Channel 1 (electrode 1)
+PB5   ------> Channel 2 (electrode 2)
+PB6   ------> Channel 3 (sampling capacitor)
+PB7   ------> Channel 4 (unused)
+*/
+#define get_sampling_cap_io() TSC_GROUP2_IO3
+#define get_sampling_cap_pin() LL_GPIO_PIN_6
+#define get_first_electrode_io() TSC_GROUP2_IO1
+#define get_first_electrode_pin() LL_GPIO_PIN_4
+#define get_second_electrode_io() TSC_GROUP2_IO2
+#define get_second_electrode_pin() LL_GPIO_PIN_5
+#define get_tsc_threshold() 45
 
 void tsc_init(void)
 {
@@ -14,11 +26,7 @@ void tsc_init(void)
     // Enable TSC clock
     RCC->AHB1ENR |= (1<<16);
 
-    /** TSC GPIO Configuration
-    PA4   ------> Channel 1
-    PA5   ------> Channel 2
-    */
-    GPIO_InitStruct.Pin = LL_GPIO_PIN_5|LL_GPIO_PIN_4;
+    GPIO_InitStruct.Pin = get_first_electrode_pin() | get_second_electrode_pin();
     GPIO_InitStruct.Mode = LL_GPIO_MODE_ALTERNATE;
     GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_LOW;
     GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_PUSHPULL;
@@ -26,15 +34,12 @@ void tsc_init(void)
     GPIO_InitStruct.Alternate = LL_GPIO_AF_9;
     LL_GPIO_Init(GPIOB, &GPIO_InitStruct);
 
-    /** TSC GPIO Configuration
-    PA6   ------> sampling cap
-    */
-    GPIO_InitStruct.Pin = LL_GPIO_PIN_6;
+    GPIO_InitStruct.Pin = get_sampling_cap_pin();
     GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_OPENDRAIN;
     LL_GPIO_Init(GPIOB, &GPIO_InitStruct);
 
     // Channel IOs
-    uint32_t channel_ios = TSC_GROUP2_IO1 | TSC_GROUP2_IO2;
+    uint32_t channel_ios = get_first_electrode_io() | get_second_electrode_io();
 
     // enable
     TSC->CR = TSC_CR_TSCE;
@@ -44,7 +49,7 @@ void tsc_init(void)
                            (uint32_t)(1 << TSC_CR_SSD_Pos) |
                            TSC_SS_PRESC_DIV1 |
                            TSC_PG_PRESC_DIV16 |
-                           TSC_MCV_16383 |
+                           TSC_MCV_255 |
                            TSC_SYNC_POLARITY_FALLING |
                            TSC_ACQ_MODE_NORMAL);
 
@@ -55,10 +60,10 @@ void tsc_init(void)
     }
 
     // Schmitt trigger and hysteresis
-    TSC->IOHCR = (uint32_t)(~(channel_ios | 0 | TSC_GROUP2_IO3));
+    TSC->IOHCR = (uint32_t)(~(channel_ios | 0 | get_sampling_cap_io()));
 
     // Sampling IOs
-    TSC->IOSCR = TSC_GROUP2_IO3;
+    TSC->IOSCR = get_sampling_cap_io();
 
     // Groups
     uint32_t grps = 0x02;
@@ -106,31 +111,39 @@ uint32_t tsc_read_button(uint32_t index)
     switch(index)
     {
         case 0:
-            tsc_set_electrode(ELECTRODE_0);
+            tsc_set_electrode(get_first_electrode_io());
             break;
         case 1:
-            tsc_set_electrode(ELECTRODE_1);
+            tsc_set_electrode(get_second_electrode_io());
             break;
     }
     tsc_start_acq();
     tsc_wait_on_acq();
-    return tsc_read(1) < 45;
+    return tsc_read(1) < get_tsc_threshold();
 }
 
-int tsc_sensor_exists(void)
-{
-    static uint8_t does = 0;
-    if (does) return 1;
+#define PIN_SHORTED_UNDEF 0
+#define PIN_SHORTED_YES 1
+#define PIN_SHORTED_NO 2
 
-    LL_GPIO_SetPinMode(GPIOB, (1 << 1), LL_GPIO_MODE_INPUT);
-    LL_GPIO_SetPinPull(GPIOB, (1 << 1), LL_GPIO_PULL_UP);
+int pin_grounded(GPIO_TypeDef* bank, int pin_mask) {
+    LL_GPIO_SetPinMode(bank, (pin_mask), LL_GPIO_MODE_INPUT);
+    LL_GPIO_SetPinPull(bank, (pin_mask), LL_GPIO_PULL_UP);
 
     // Short delay before reading pin
     asm("nop"); asm("nop"); asm("nop"); asm("nop");
 
-    does = (LL_GPIO_ReadInputPort(GPIOB) & (1 << 1)) == 0;
+    int result = (LL_GPIO_ReadInputPort(bank) & (pin_mask)) == 0;
+
+    LL_GPIO_SetPinPull(bank, 1, LL_GPIO_PULL_NO);
 
-    LL_GPIO_SetPinPull(GPIOB, 1, LL_GPIO_PULL_NO);
+    return result ? PIN_SHORTED_YES : PIN_SHORTED_NO;
+}
 
-    return does;
+int tsc_sensor_exists(void)
+{
+    // PB1 is grounded in USB A nano & USB C touch
+    static uint8_t does = PIN_SHORTED_UNDEF;
+    if (does == PIN_SHORTED_UNDEF) does = pin_grounded(GPIOB, LL_GPIO_PIN_1);
+    return does == PIN_SHORTED_YES;
 }