diff --git a/README.md b/README.md
index 2be14a1..8a6ddd0 100644
--- a/README.md
+++ b/README.md
@@ -26,7 +26,7 @@ $ pip3 install --user adafruit-nrfutil
 
 This repository depends on the following submodules:
 
-- [tinyusb](https://github.com/hathach/tinyusb/tree/develop)
+- [tinyusb](https://github.com/hathach/tinyusb)
 - [nrfx](https://github.com/NordicSemiconductor/nrfx)
 
 Note that `tinyusb` also includes `nrfx` as a submodule, so you need
diff --git a/src/boards.c b/src/boards.c
index 0d6d30a..55c285a 100644
--- a/src/boards.c
+++ b/src/boards.c
@@ -82,6 +82,7 @@ void board_init(void)
   app_timer_init();
 
   // Configure Systick for led blinky
+  NVIC_SetPriority(SysTick_IRQn, 7);
   extern uint32_t SystemCoreClock;
   SysTick_Config(SystemCoreClock/1000);
 }
@@ -346,9 +347,11 @@ void neopixel_init(void)
 void neopixel_teardown(void)
 {
   uint8_t grb[3] = { 0, 0, 0 };
-  neopixel_write(grb);
 
-  NRFX_DELAY_US(100);
+  NRFX_DELAY_US(50);  // wait for previous write is complete
+
+  neopixel_write(grb);
+  NRFX_DELAY_US(50);  // wait for this write
 
   pwm_teardown(NRF_PWM2);
 }
@@ -380,6 +383,10 @@ void neopixel_write (uint8_t *pixels)
   nrf_pwm_seq_cnt_set(pwm, 0, sizeof(pixels_pattern)/2);
   nrf_pwm_event_clear(pwm, NRF_PWM_EVENT_SEQEND0);
   nrf_pwm_task_trigger(pwm, NRF_PWM_TASK_SEQSTART0);
+
+  // no need to blocking wait for sequence complete
+//  while( !nrf_pwm_event_check(pwm, NRF_PWM_EVENT_SEQEND0) ) {}
+//  nrf_pwm_event_clear(pwm, NRF_PWM_EVENT_SEQEND0);
 }
 #endif
 
diff --git a/src/usb/uf2/ghostfat.c b/src/usb/uf2/ghostfat.c
index bea65b6..f4311cf 100644
--- a/src/usb/uf2/ghostfat.c
+++ b/src/usb/uf2/ghostfat.c
@@ -83,7 +83,7 @@ static struct TextFile const info[] = {
 };
 #define NUM_INFO (sizeof(info) / sizeof(info[0]))
 
-#define UF2_SIZE           (get_flash_size() * 2)
+#define UF2_SIZE           (current_flash_size() * 2)
 #define UF2_SECTORS        (UF2_SIZE / 512)
 #define UF2_FIRST_SECTOR   (NUM_INFO + 1)
 #define UF2_LAST_SECTOR    (UF2_FIRST_SECTOR + UF2_SECTORS - 1)
@@ -120,7 +120,9 @@ static FAT_BootBlock const BootBlock = {
 #define NRF_LOG_WARNING(...)
 
 static WriteState _wr_state = { 0 };
-static uint32_t get_flash_size(void)
+
+// get current.uf2 flash size in bytes, round up to 256 bytes
+static uint32_t current_flash_size(void)
 {
   static uint32_t flash_sz = 0;
 
@@ -136,10 +138,17 @@ static uint32_t get_flash_size(void)
       bootloader_settings_t const * boot_setting;
       bootloader_util_settings_get(&boot_setting);
 
+      flash_sz = boot_setting->bank_0_size;
+
+      // Copy size must be multiple of 256 bytes
+      // else we will got an issue copying current.uf2
+      if (flash_sz & 0xff)
+      {
+        flash_sz = (flash_sz & ~0xff) + 256;
+      }
+
       // if bank0 size is not valid, happens when flashed with jlink
       // use maximum application size
-
-      flash_sz = boot_setting->bank_0_size;
       if ( (flash_sz == 0) || (flash_sz == 0xFFFFFFFFUL) )
       {
         flash_sz = FLASH_SIZE;
@@ -217,7 +226,7 @@ void read_block(uint32_t block_no, uint8_t *data) {
                 bl->magicStart1 = UF2_MAGIC_START1;
                 bl->magicEnd = UF2_MAGIC_END;
                 bl->blockNo = sectionIdx;
-                bl->numBlocks = FLASH_SIZE / 256;
+                bl->numBlocks = current_flash_size() / 256;
                 bl->targetAddr = addr;
                 bl->payloadSize = 256;
                 bl->flags = UF2_FLAG_FAMILYID;