diff --git a/stmhal/boards/PYBLITEV10/mpconfigboard.h b/stmhal/boards/PYBLITEV10/mpconfigboard.h
index 037302c6ba..fb839888cb 100644
--- a/stmhal/boards/PYBLITEV10/mpconfigboard.h
+++ b/stmhal/boards/PYBLITEV10/mpconfigboard.h
@@ -82,7 +82,6 @@
 
 // USB config
 #define MICROPY_HW_USB_VBUS_DETECT_PIN (pin_A9)
-#define MICROPY_HW_USE_ALT_IRQ_FOR_CDC (1)
 
 // MMA accelerometer config
 #define MICROPY_HW_MMA_AVDD_PIN     (pin_A10)
diff --git a/stmhal/led.c b/stmhal/led.c
index 990d2046a1..ee03d3fd00 100644
--- a/stmhal/led.c
+++ b/stmhal/led.c
@@ -83,46 +83,12 @@ void led_init(void) {
         GPIO_InitStructure.Pin = led_pin->pin_mask;
         HAL_GPIO_Init(led_pin->gpio, &GPIO_InitStructure);
     }
-
-    #if MICROPY_HW_LED4_PWM
-    // LED4 (blue) is on PB4 which is TIM3_CH1
-    // we use PWM on this channel to fade the LED
-
-    // LED3 (yellow) is on PA15 which has TIM2_CH1, so we could PWM that as well
-
-    // GPIO configuration
-    GPIO_InitStructure.Pin = MICROPY_HW_LED4.pin_mask;
-    GPIO_InitStructure.Mode = GPIO_MODE_AF_PP;
-    GPIO_InitStructure.Speed = GPIO_SPEED_FAST;
-    GPIO_InitStructure.Pull = GPIO_NOPULL;
-    GPIO_InitStructure.Alternate = GPIO_AF2_TIM3;
-    HAL_GPIO_Init(MICROPY_HW_LED4.gpio, &GPIO_InitStructure);
-
-    // PWM mode configuration
-    TIM_OC_InitTypeDef oc_init;
-    oc_init.OCMode = TIM_OCMODE_PWM1;
-    oc_init.Pulse = 0; // off
-    oc_init.OCPolarity = TIM_OCPOLARITY_HIGH;
-    oc_init.OCFastMode = TIM_OCFAST_DISABLE;
-    HAL_TIM_PWM_ConfigChannel(&TIM3_Handle, &oc_init, TIM_CHANNEL_1);
-
-    // start PWM
-    TIM_CCxChannelCmd(TIM3, TIM_CHANNEL_1, TIM_CCx_ENABLE);
-    #endif
 }
 
 void led_state(pyb_led_t led, int state) {
     if (led < 1 || led > NUM_LEDS) {
         return;
     }
-    if (MICROPY_HW_LED4_PWM && led == 4) {
-        if (state) {
-            TIM3->CCR1 = 0xffff;
-        } else {
-            TIM3->CCR1 = 0;
-        }
-        return;
-    }
     const pin_obj_t *led_pin = pyb_led_obj[led - 1].led_pin;
     //printf("led_state(%d,%d)\n", led, state);
     if (state == 0) {
@@ -139,15 +105,6 @@ void led_toggle(pyb_led_t led) {
         return;
     }
 
-    if (MICROPY_HW_LED4_PWM && led == 4) {
-        if (TIM3->CCR1 == 0) {
-            TIM3->CCR1 = 0xffff;
-        } else {
-            TIM3->CCR1 = 0;
-        }
-        return;
-    }
-
     // toggle the output data register to toggle the LED state
     const pin_obj_t *led_pin = pyb_led_obj[led - 1].led_pin;
     led_pin->gpio->ODR ^= led_pin->pin_mask;
@@ -158,14 +115,6 @@ int led_get_intensity(pyb_led_t led) {
         return 0;
     }
 
-    if (MICROPY_HW_LED4_PWM && led == 4) {
-        mp_uint_t i = (TIM3->CCR1 * 255 + (USBD_CDC_POLLING_INTERVAL*1000) - 2) / ((USBD_CDC_POLLING_INTERVAL*1000) - 1);
-        if (i > 255) {
-            i = 255;
-        }
-        return i;
-    }
-
     const pin_obj_t *led_pin = pyb_led_obj[led - 1].led_pin;
     GPIO_TypeDef *gpio = led_pin->gpio;
 
@@ -180,19 +129,6 @@ int led_get_intensity(pyb_led_t led) {
 }
 
 void led_set_intensity(pyb_led_t led, mp_int_t intensity) {
-    if (MICROPY_HW_LED4_PWM && led == 4) {
-        // set intensity using PWM pulse width
-        if (intensity < 0) {
-            intensity = 0;
-        } else if (intensity >= 255) {
-            intensity = 0xffff;
-        } else {
-            intensity = intensity * ((USBD_CDC_POLLING_INTERVAL*1000) - 1) / 255;
-        }
-        TIM3->CCR1 = intensity;
-        return;
-    }
-
     // intensity not supported for this LED; just turn it on/off
     led_state(led, intensity > 0);
 }
diff --git a/stmhal/main.c b/stmhal/main.c
index 0e5fc44af3..882de6e1a4 100644
--- a/stmhal/main.c
+++ b/stmhal/main.c
@@ -395,12 +395,6 @@ int main(void) {
 
     // basic sub-system init
     pendsv_init();
-    #if defined(MICROPY_HW_USE_ALT_IRQ_FOR_CDC)
-    HAL_NVIC_SetPriority(PVD_IRQn, 6, 0); // same priority as USB
-    HAL_NVIC_EnableIRQ(PVD_IRQn);
-    #else
-    timer_tim3_init();
-    #endif
     led_init();
 #if MICROPY_HW_HAS_SWITCH
     switch_init0();
diff --git a/stmhal/modmachine.c b/stmhal/modmachine.c
index 7f72359be6..6d71f5c627 100644
--- a/stmhal/modmachine.c
+++ b/stmhal/modmachine.c
@@ -253,7 +253,7 @@ STATIC mp_obj_t machine_freq(mp_uint_t n_args, const mp_obj_t *args) {
         //printf("%lu %lu %lu %lu %lu\n", sysclk_source, m, n, p, q);
 
         // let the USB CDC have a chance to process before we change the clock
-        HAL_Delay(USBD_CDC_POLLING_INTERVAL + 2);
+        HAL_Delay(5);
 
         // desired system clock source is in sysclk_source
         RCC_ClkInitTypeDef RCC_ClkInitStruct;
@@ -316,9 +316,6 @@ STATIC mp_obj_t machine_freq(mp_uint_t n_args, const mp_obj_t *args) {
             }
         }
 
-        // re-init TIM3 for USB CDC rate
-        timer_tim3_init();
-
         #if defined(MICROPY_HW_CLK_LAST_FREQ) && MICROPY_HW_CLK_LAST_FREQ
         #if defined(MCU_SERIES_F7)
         #define FREQ_BKP BKP31R
diff --git a/stmhal/stm32_it.c b/stmhal/stm32_it.c
index 57b5d85302..4d3ffdffe2 100644
--- a/stmhal/stm32_it.c
+++ b/stmhal/stm32_it.c
@@ -278,12 +278,6 @@ void SysTick_Handler(void) {
     // be generalised in the future then a dispatch table can be used as
     // follows: ((void(*)(void))(systick_dispatch[uwTick & 0xf]))();
 
-    #if defined(MICROPY_HW_USE_ALT_IRQ_FOR_CDC)
-    if (((uwTick) & 7) == 4) { // every 8ms
-        NVIC->STIR = PVD_IRQn;
-    }
-    #endif
-
     if (STORAGE_IDLE_TICK(uwTick)) {
         NVIC->STIR = FLASH_IRQn;
     }
@@ -479,8 +473,6 @@ void EXTI15_10_IRQHandler(void) {
 
 void PVD_IRQHandler(void) {
     IRQ_ENTER(PVD_IRQn);
-    #if defined(MICROPY_HW_USE_ALT_IRQ_FOR_CDC)
-    #endif
     Handle_EXTI_Irq(EXTI_PVD_OUTPUT);
     IRQ_EXIT(PVD_IRQn);
 }
@@ -539,11 +531,7 @@ void TIM2_IRQHandler(void) {
 
 void TIM3_IRQHandler(void) {
     IRQ_ENTER(TIM3_IRQn);
-    #if defined(MICROPY_HW_USE_ALT_IRQ_FOR_CDC)
     timer_irq_handler(3);
-    #else
-    HAL_TIM_IRQHandler(&TIM3_Handle);
-    #endif
     IRQ_EXIT(TIM3_IRQn);
 }
 
diff --git a/stmhal/timer.c b/stmhal/timer.c
index 850e0c8298..9caa056a2f 100644
--- a/stmhal/timer.c
+++ b/stmhal/timer.c
@@ -68,7 +68,7 @@
 ///     tim.callback(lambda t: ...)     # set callback for update interrupt (t=tim instance)
 ///     tim.callback(None)              # clear callback
 ///
-/// *Note:* Timer 3 is reserved for internal use.  Timer 5 controls
+/// *Note:* Timer 3 is used for fading the blue LED.  Timer 5 controls
 /// the servo driver, and Timer 6 is used for timed ADC/DAC reading/writing.
 /// It is recommended to use the other timers in your programs.
 
@@ -76,8 +76,6 @@
 // the interrupts to be dispatched, so they are all collected here.
 //
 // TIM3:
-//  - flash storage controller, to flush the cache
-//  - USB CDC interface, interval, to check for new data
 //  - LED 4, PWM to set the LED intensity
 //
 // TIM5:
@@ -144,7 +142,6 @@ typedef struct _pyb_timer_obj_t {
 #define TIMER_CNT_MASK(self)    ((self)->is_32bit ? 0xffffffff : 0xffff)
 #define TIMER_CHANNEL(self)     ((((self)->channel) - 1) << 2)
 
-TIM_HandleTypeDef TIM3_Handle;
 TIM_HandleTypeDef TIM5_Handle;
 TIM_HandleTypeDef TIM6_Handle;
 
@@ -171,34 +168,6 @@ void timer_deinit(void) {
     }
 }
 
-// TIM3 is set-up for the USB CDC interface
-void timer_tim3_init(void) {
-    // set up the timer for USBD CDC
-    __TIM3_CLK_ENABLE();
-
-    TIM3_Handle.Instance = TIM3;
-    TIM3_Handle.Init.Period = (USBD_CDC_POLLING_INTERVAL*1000) - 1; // TIM3 fires every USBD_CDC_POLLING_INTERVAL ms
-    TIM3_Handle.Init.Prescaler = timer_get_source_freq(3) / 1000000 - 1; // TIM3 runs at 1MHz
-    TIM3_Handle.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
-    TIM3_Handle.Init.CounterMode = TIM_COUNTERMODE_UP;
-    HAL_TIM_Base_Init(&TIM3_Handle);
-
-    HAL_NVIC_SetPriority(TIM3_IRQn, IRQ_PRI_TIM3, IRQ_SUBPRI_TIM3);
-    HAL_NVIC_EnableIRQ(TIM3_IRQn);
-
-    if (HAL_TIM_Base_Start(&TIM3_Handle) != HAL_OK) {
-        /* Starting Error */
-    }
-}
-
-/* unused
-void timer_tim3_deinit(void) {
-    // reset TIM3 timer
-    __TIM3_FORCE_RESET();
-    __TIM3_RELEASE_RESET();
-}
-*/
-
 // TIM5 is set-up for the servo controller
 // This function inits but does not start the timer
 void timer_tim5_init(void) {
@@ -250,10 +219,6 @@ TIM_HandleTypeDef *timer_tim6_init(uint freq) {
 
 // Interrupt dispatch
 void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim) {
-    #if !defined(MICROPY_HW_USE_ALT_IRQ_FOR_CDC)
-    if (htim == &TIM3_Handle) {
-    } else
-    #endif
     if (htim == &TIM5_Handle) {
         servo_timer_irq_callback();
     }
@@ -655,11 +620,7 @@ STATIC mp_obj_t pyb_timer_make_new(const mp_obj_type_t *type, mp_uint_t n_args,
     switch (tim->tim_id) {
         case 1: tim->tim.Instance = TIM1; tim->irqn = TIM1_UP_TIM10_IRQn; break;
         case 2: tim->tim.Instance = TIM2; tim->irqn = TIM2_IRQn; tim->is_32bit = true; break;
-        #if defined(MICROPY_HW_USE_ALT_IRQ_FOR_CDC)
         case 3: tim->tim.Instance = TIM3; tim->irqn = TIM3_IRQn; break;
-        #else
-        case 3: nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "Timer 3 is for internal use only")); // TIM3 used for low-level stuff; go via regs if necessary
-        #endif
         case 4: tim->tim.Instance = TIM4; tim->irqn = TIM4_IRQn; break;
         case 5: tim->tim.Instance = TIM5; tim->irqn = TIM5_IRQn; tim->is_32bit = true; break;
         #if defined(TIM6)
diff --git a/stmhal/timer.h b/stmhal/timer.h
index 8988197c0f..89b3c79f4f 100644
--- a/stmhal/timer.h
+++ b/stmhal/timer.h
@@ -24,18 +24,11 @@
  * THE SOFTWARE.
  */
 
-// Periodically, the state of the buffer "UserTxBuffer" is checked.
-// The period depends on USBD_CDC_POLLING_INTERVAL
-// The value is in ms. The max is 65 and the min is 1.
-#define USBD_CDC_POLLING_INTERVAL (10)
-
-extern TIM_HandleTypeDef TIM3_Handle;
 extern TIM_HandleTypeDef TIM5_Handle;
 
 extern const mp_obj_type_t pyb_timer_type;
 
 void timer_init0(void);
-void timer_tim3_init(void);
 void timer_tim5_init(void);
 TIM_HandleTypeDef *timer_tim6_init(uint freq);
 
diff --git a/stmhal/usbd_cdc_interface.c b/stmhal/usbd_cdc_interface.c
index 801bcb753d..b42d3e2194 100644
--- a/stmhal/usbd_cdc_interface.c
+++ b/stmhal/usbd_cdc_interface.c
@@ -140,10 +140,6 @@ static int8_t CDC_Itf_Init(void)
   TIM_Config();
 #endif
   
-    /*##-4- Start the TIM Base generation in interrupt mode ####################*/
-    /* Start Channel1 */
-    __HAL_TIM_ENABLE_IT(&TIM3_Handle, TIM_IT_UPDATE);
-  
     /*##-5- Set Application Buffers ############################################*/
     USBD_CDC_SetTxBuffer(&hUSBDDevice, UserTxBuffer, 0);
     USBD_CDC_SetRxBuffer(&hUSBDDevice, UserRxBuffer);