path: root/watch-library/hardware/watch/watch_private.c

/*
 * MIT License
 *
 * Copyright (c) 2020 Joey Castillo
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "watch_private.h"
#include "watch_utility.h"
#include "tusb.h"

void _watch_init(void) {
    // disable the LED pin (it may have been enabled by the bootloader)
    watch_disable_digital_output(GPIO(GPIO_PORTA, 20));

    // RAM should be back-biased in STANDBY
    PM->STDBYCFG.bit.BBIASHS = 1;

    // Use switching regulator for lower power consumption.
    SUPC->VREG.bit.SEL = 1;
    while(!SUPC->STATUS.bit.VREGRDY); // wait for voltage regulator to become ready

    // check the battery voltage...
    watch_enable_adc();
    uint16_t battery_voltage = watch_get_vcc_voltage();
    watch_disable_adc();
    // ...because we can enable the more efficient low power regulator if the system voltage is > 2.5V
    // still, enable LPEFF only if the battery voltage is comfortably above this threshold.
    if (battery_voltage >= 2700) {
        SUPC->VREG.bit.LPEFF = 1;
    } else {
        SUPC->VREG.bit.LPEFF = 0;
    }

    // set up the brownout detector (low battery warning)
    NVIC_DisableIRQ(SYSTEM_IRQn);
    NVIC_ClearPendingIRQ(SYSTEM_IRQn);
    NVIC_EnableIRQ(SYSTEM_IRQn);
    SUPC->BOD33.bit.ENABLE = 0;     // BOD33 must be disabled to change its configuration
    SUPC->BOD33.bit.VMON = 0;       // Monitor VDD in active and standby mode
    SUPC->BOD33.bit.ACTCFG = 1;     // Enable sampling mode when active
    SUPC->BOD33.bit.RUNSTDBY = 1;   // Enable sampling mode in standby
    SUPC->BOD33.bit.STDBYCFG = 1;   // Run in standby
    SUPC->BOD33.bit.RUNBKUP = 0;    // Don't run in backup mode
    SUPC->BOD33.bit.PSEL = 0x9;     // Check battery level every second (we'll change this before entering sleep)
    SUPC->BOD33.bit.LEVEL = 34;     // Detect brownout at 2.6V (1.445V + level * 34mV)
    SUPC->BOD33.bit.ACTION = 0x2;   // Generate an interrupt when BOD33 is triggered
    SUPC->BOD33.bit.HYST = 0;       // Disable hysteresis
    while(!SUPC->STATUS.bit.B33SRDY); // wait for BOD33 to sync

    // Enable interrupt on BOD33 detect
    SUPC->INTENSET.bit.BOD33DET = 1;
    SUPC->BOD33.bit.ENABLE = 1;

    // External wake depends on RTC; calendar is a required module.
    _watch_rtc_init();

    // set up state
    btn_alarm_callback = NULL;
    a2_callback = NULL;
    a4_callback = NULL;
}

static inline void _watch_wait_for_entropy() {
    while (!hri_trng_get_INTFLAG_reg(TRNG, TRNG_INTFLAG_DATARDY));
}

// this function is called by arc4random to get entropy for random number generation.
int getentropy(void *buf, size_t buflen);

// let's use the SAM L22's true random number generator to seed the PRNG!
int getentropy(void *buf, size_t buflen) {
    hri_mclk_set_APBCMASK_TRNG_bit(MCLK);
    hri_trng_set_CTRLA_ENABLE_bit(TRNG);

    size_t i = 0;
    while(i < buflen / 4) {
        _watch_wait_for_entropy();
        ((uint32_t *)buf)[i++] = hri_trng_read_DATA_reg(TRNG);
    }

    // but what if they asked for an awkward number of bytes?
    if (buflen % 4) {
        // all good: let's fill in one, two or three bytes at the end of the buffer.
        _watch_wait_for_entropy();
        uint32_t last_little_bit = hri_trng_read_DATA_reg(TRNG);
        for(size_t j = 0; j <= (buflen % 4); j++) {
            ((uint8_t *)buf)[i * 4 + j] = (last_little_bit >> (j * 8)) & 0xFF;
        }
    }

    hri_trng_clear_CTRLA_ENABLE_bit(TRNG);
    hri_mclk_clear_APBCMASK_TRNG_bit(MCLK);

    return 0;
}

void _watch_enable_tcc(void) {
    // clock TCC0 with the main clock (8 MHz) and enable the peripheral clock.
    hri_gclk_write_PCHCTRL_reg(GCLK, TCC0_GCLK_ID, GCLK_PCHCTRL_GEN_GCLK0_Val | GCLK_PCHCTRL_CHEN);
    hri_mclk_set_APBCMASK_TCC0_bit(MCLK);
    // disable and reset TCC0.
    hri_tcc_clear_CTRLA_ENABLE_bit(TCC0);
    hri_tcc_wait_for_sync(TCC0, TCC_SYNCBUSY_ENABLE);
    hri_tcc_write_CTRLA_reg(TCC0, TCC_CTRLA_SWRST);
    hri_tcc_wait_for_sync(TCC0, TCC_SYNCBUSY_SWRST);
    // divide the clock down to 1 MHz
    if (hri_usbdevice_get_CTRLA_ENABLE_bit(USB)) {
        // if USB is enabled, we are running an 8 MHz clock.
        hri_tcc_write_CTRLA_reg(TCC0, TCC_CTRLA_PRESCALER_DIV8);
    } else {
        // otherwise it's 4 Mhz.
        hri_tcc_write_CTRLA_reg(TCC0, TCC_CTRLA_PRESCALER_DIV4);
    }
    // We're going to use normal PWM mode, which means period is controlled by PER, and duty cycle is controlled by
    // each compare channel's value:
    //  * Buzzer tones are set by setting PER to the desired period for a given frequency, and CC[1] to half of that
    //    period (i.e. a square wave with a 50% duty cycle).
    //  * LEDs on CC[2] and CC[3] can be set to any value from 0 (off) to PER (fully on).
    hri_tcc_write_WAVE_reg(TCC0, TCC_WAVE_WAVEGEN_NPWM);
    #ifdef WATCH_INVERT_LED_POLARITY
    // This is here for the dev board, which uses a common anode LED (instead of common cathode like the actual watch).
    hri_tcc_set_WAVE_reg(TCC0, (1 << (TCC_WAVE_POL0_Pos + WATCH_RED_TCC_CHANNEL)) |
                               (1 << (TCC_WAVE_POL0_Pos + WATCH_GREEN_TCC_CHANNEL)));
    #endif
    // The buzzer will set the period depending on the tone it wants to play, but we have to set some period here to
    // get the LED working. Almost any period will do, tho it should be below 20000 (i.e. 50 Hz) to avoid flickering.
    hri_tcc_write_PER_reg(TCC0, 4096);
    // Set the duty cycle of all pins to 0: LED's off, buzzer not buzzing.
    hri_tcc_write_CC_reg(TCC0, WATCH_BUZZER_TCC_CHANNEL, 0);
    hri_tcc_write_CC_reg(TCC0, WATCH_RED_TCC_CHANNEL, 0);
    hri_tcc_write_CC_reg(TCC0, WATCH_GREEN_TCC_CHANNEL, 0);
    // Enable the TCC
    hri_tcc_set_CTRLA_ENABLE_bit(TCC0);
    hri_tcc_wait_for_sync(TCC0, TCC_SYNCBUSY_ENABLE);

    // enable LED PWM pins (the LED driver assumes if the TCC is on, the pins are enabled)
    gpio_set_pin_direction(RED, GPIO_DIRECTION_OUT);
    gpio_set_pin_function(RED, WATCH_RED_TCC_PINMUX);
    gpio_set_pin_direction(GREEN, GPIO_DIRECTION_OUT);
    gpio_set_pin_function(GREEN, WATCH_GREEN_TCC_PINMUX);
}

void _watch_disable_tcc(void) {
    // disable all PWM pins
    gpio_set_pin_direction(BUZZER, GPIO_DIRECTION_OFF);
    gpio_set_pin_function(BUZZER, GPIO_PIN_FUNCTION_OFF);
    gpio_set_pin_direction(RED, GPIO_DIRECTION_OFF);
    gpio_set_pin_function(RED, GPIO_PIN_FUNCTION_OFF);
    gpio_set_pin_direction(GREEN, GPIO_DIRECTION_OFF);
    gpio_set_pin_function(GREEN, GPIO_PIN_FUNCTION_OFF);

    // disable the TCC
    hri_tcc_clear_CTRLA_ENABLE_bit(TCC0);
    hri_mclk_clear_APBCMASK_TCC0_bit(MCLK);
}

void _watch_enable_usb(void) {
    // disable USB, just in case.
    hri_usb_clear_CTRLA_ENABLE_bit(USB);

    // bump clock up to 8 MHz
    hri_oscctrl_write_OSC16MCTRL_FSEL_bf(OSCCTRL, OSCCTRL_OSC16MCTRL_FSEL_8_Val);

    // reset flags and disable DFLL
    OSCCTRL->INTFLAG.reg = OSCCTRL_INTFLAG_DFLLRDY;
    OSCCTRL->DFLLCTRL.reg = 0;
    while (!(OSCCTRL->STATUS.reg & OSCCTRL_STATUS_DFLLRDY));

    // set the coarse and fine values to speed up frequency lock.
    uint32_t coarse =(*((uint32_t *)NVMCTRL_OTP5)) >> 26;
    OSCCTRL->DFLLVAL.reg = OSCCTRL_DFLLVAL_COARSE(coarse) |
                           OSCCTRL_DFLLVAL_FINE(0x200);
    // set coarse and fine steps, and multiplier (48 MHz = 32768 Hz * 1465)
    OSCCTRL->DFLLMUL.reg = OSCCTRL_DFLLMUL_CSTEP( 1 ) |
                           OSCCTRL_DFLLMUL_FSTEP( 1 ) |
                           OSCCTRL_DFLLMUL_MUL( 1465 );
    // set closed loop mode, chill cycle disable and USB clock recovery mode, and enable the DFLL.
    OSCCTRL->DFLLCTRL.reg = OSCCTRL_DFLLCTRL_MODE | OSCCTRL_DFLLCTRL_CCDIS | OSCCTRL_DFLLCTRL_ONDEMAND | OSCCTRL_DFLLCTRL_RUNSTDBY | OSCCTRL_DFLLCTRL_USBCRM | OSCCTRL_DFLLCTRL_ENABLE;
    while (!(OSCCTRL->STATUS.reg & OSCCTRL_STATUS_DFLLRDY));

    // assign DFLL to GCLK1
    GCLK->GENCTRL[1].reg = GCLK_GENCTRL_SRC(GCLK_GENCTRL_SRC_DFLL48M) | GCLK_GENCTRL_DIV(1) | GCLK_GENCTRL_GENEN;// | GCLK_GENCTRL_OE;
    while (GCLK->SYNCBUSY.bit.GENCTRL1); // wait for generator control 1 to sync

    // assign GCLK1 to USB
    hri_gclk_write_PCHCTRL_reg(GCLK, USB_GCLK_ID, GCLK_PCHCTRL_GEN_GCLK1_Val | GCLK_PCHCTRL_CHEN);
    hri_mclk_set_AHBMASK_USB_bit(MCLK);
    hri_mclk_set_APBBMASK_USB_bit(MCLK);

    // USB Pin Init
    gpio_set_pin_direction(PIN_PA24, GPIO_DIRECTION_OUT);
    gpio_set_pin_level(PIN_PA24, false);
    gpio_set_pin_pull_mode(PIN_PA24, GPIO_PULL_OFF);
    gpio_set_pin_direction(PIN_PA25, GPIO_DIRECTION_OUT);
    gpio_set_pin_level(PIN_PA25, false);
    gpio_set_pin_pull_mode(PIN_PA25, GPIO_PULL_OFF);

    gpio_set_pin_function(PIN_PA24, PINMUX_PA24G_USB_DM);
    gpio_set_pin_function(PIN_PA25, PINMUX_PA25G_USB_DP);

    // before we init TinyUSB, we are going to need a periodic callback to handle TinyUSB tasks.
    // TC2 and TC3 are reserved for devices on the 9-pin connector, so let's use TC0.
    // clock TC0 with the 8 MHz clock on GCLK0.
    hri_gclk_write_PCHCTRL_reg(GCLK, TC0_GCLK_ID, GCLK_PCHCTRL_GEN_GCLK0_Val | GCLK_PCHCTRL_CHEN);
    // and enable the peripheral clock.
    hri_mclk_set_APBCMASK_TC0_bit(MCLK);
    // disable and reset TC0.
    hri_tc_clear_CTRLA_ENABLE_bit(TC0);
    hri_tc_wait_for_sync(TC0, TC_SYNCBUSY_ENABLE);
    hri_tc_write_CTRLA_reg(TC0, TC_CTRLA_SWRST);
    hri_tc_wait_for_sync(TC0, TC_SYNCBUSY_SWRST);
    // configure the TC to overflow 1,000 times per second
    hri_tc_write_CTRLA_reg(TC0, TC_CTRLA_PRESCALER_DIV64 |  // divide the 8 MHz clock by 64 to count at 125 KHz
                                TC_CTRLA_MODE_COUNT8 |      // count in 8-bit mode
                                TC_CTRLA_RUNSTDBY);         // run in standby, just in case we figure that out
    hri_tccount8_write_PER_reg(TC0, 125);                   // 125000 Hz / 125 = 1,000 Hz
    // set an interrupt on overflow; this will call TC0_Handler below.
    hri_tc_set_INTEN_OVF_bit(TC0);
    NVIC_ClearPendingIRQ(TC0_IRQn);
    NVIC_EnableIRQ (TC0_IRQn);

    // now we can init TinyUSB
    tusb_init();
    // and start the timer that handles USB device tasks.
    hri_tc_set_CTRLA_ENABLE_bit(TC0);
}

// this function ends up getting called by printf to log stuff to the USB console.
int _write(int file, char *ptr, int len) {
    (void)file;
    if (hri_usbdevice_get_CTRLA_ENABLE_bit(USB)) {
        tud_cdc_n_write(0, (void const*)ptr, len);
        tud_cdc_n_write_flush(0);
        return len;
    }

    return 0;
}

// this method could be overridden to read stuff from the USB console? but no need rn.
int _read(void) {
    return 0;
}

void USB_Handler(void) {
    tud_int_handler(0);
}

void TC0_Handler(void) {
    tud_task();
    TC0->COUNT8.INTFLAG.reg |= TC_INTFLAG_OVF;
}


// USB Descriptors and tinyUSB callbacks follow.

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2019 Ha Thach (tinyusb.org)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 */

//--------------------------------------------------------------------+
// Device Descriptors
//--------------------------------------------------------------------+
tusb_desc_device_t const desc_device =
{
    .bLength            = sizeof(tusb_desc_device_t),
    .bDescriptorType    = TUSB_DESC_DEVICE,
    .bcdUSB             = 0x0200,

    // Use Interface Association Descriptor (IAD) for CDC
    // As required by USB Specs IAD's subclass must be common class (2) and protocol must be IAD (1)
    .bDeviceClass       = TUSB_CLASS_MISC,
    .bDeviceSubClass    = MISC_SUBCLASS_COMMON,
    .bDeviceProtocol    = MISC_PROTOCOL_IAD,

    .bMaxPacketSize0    = CFG_TUD_ENDPOINT0_SIZE,

    .idVendor           = 0x1209,
    .idProduct          = 0x2151,
    .bcdDevice          = 0x0100,

    .iManufacturer      = 0x01,
    .iProduct           = 0x02,
    .iSerialNumber      = 0x03,

    .bNumConfigurations = 0x01
};

// Invoked when received GET DEVICE DESCRIPTOR
// Application return pointer to descriptor
uint8_t const * tud_descriptor_device_cb(void) {
  return (uint8_t const *) &desc_device;
}

//--------------------------------------------------------------------+
// Configuration Descriptor
//--------------------------------------------------------------------+

enum {
  ITF_NUM_CDC = 0,
  ITF_NUM_CDC_DATA,
  ITF_NUM_MSC,
  ITF_NUM_TOTAL
};

#define CONFIG_TOTAL_LEN    (TUD_CONFIG_DESC_LEN + TUD_CDC_DESC_LEN + TUD_MSC_DESC_LEN)

#define EPNUM_CDC_NOTIF   0x81
#define EPNUM_CDC_OUT     0x02
#define EPNUM_CDC_IN      0x82

#define EPNUM_MSC_OUT     0x03
#define EPNUM_MSC_IN      0x83

uint8_t const desc_fs_configuration[] = {
  // Config number, interface count, string index, total length, attribute, power in mA
  TUD_CONFIG_DESCRIPTOR(1, ITF_NUM_TOTAL, 0, CONFIG_TOTAL_LEN, TUSB_DESC_CONFIG_ATT_REMOTE_WAKEUP, 100),

  // Interface number, string index, EP notification address and size, EP data address (out, in) and size.
  TUD_CDC_DESCRIPTOR(ITF_NUM_CDC, 4, EPNUM_CDC_NOTIF, 8, EPNUM_CDC_OUT, EPNUM_CDC_IN, 64),

  // Interface number, string index, EP Out & EP In address, EP size
  TUD_MSC_DESCRIPTOR(ITF_NUM_MSC, 5, EPNUM_MSC_OUT, EPNUM_MSC_IN, 64),
};

// Invoked when received GET CONFIGURATION DESCRIPTOR
// Application return pointer to descriptor
// Descriptor contents must exist long enough for transfer to complete
uint8_t const * tud_descriptor_configuration_cb(uint8_t index) {
    (void) index; // for multiple configurations
    return desc_fs_configuration;
}

//--------------------------------------------------------------------+
// String Descriptors
//--------------------------------------------------------------------+

// array of pointer to string descriptors
char const* string_desc_arr [] =
{
  (const char[]) { 0x09, 0x04 }, // 0: is supported language is English (0x0409)
  "TinyUSB",                     // 1: Manufacturer
  "TinyUSB Device",              // 2: Product
  "123456",                      // 3: Serials, should use chip ID
  "TinyUSB CDC",                 // 4: CDC Interface
};

static uint16_t _desc_str[32];

// Invoked when received GET STRING DESCRIPTOR request
// Application return pointer to descriptor, whose contents must exist long enough for transfer to complete
uint16_t const* tud_descriptor_string_cb(uint8_t index, uint16_t langid)
{
    (void) langid;

    uint8_t chr_count;

    if ( index == 0) {
        memcpy(&_desc_str[1], string_desc_arr[0], 2);
        chr_count = 1;
    } else {
        // Note: the 0xEE index string is a Microsoft OS 1.0 Descriptors.
        // https://docs.microsoft.com/en-us/windows-hardware/drivers/usbcon/microsoft-defined-usb-descriptors

        if ( !(index < sizeof(string_desc_arr)/sizeof(string_desc_arr[0])) ) return NULL;

        const char* str = string_desc_arr[index];

        // Cap at max char
        chr_count = strlen(str);
        if ( chr_count > 31 ) chr_count = 31;

        // Convert ASCII string into UTF-16
        for(uint8_t i=0; i<chr_count; i++)
        {
            _desc_str[1+i] = str[i];
        }
    }

    // first byte is length (including header), second byte is string type
    _desc_str[0] = (TUSB_DESC_STRING << 8 ) | (2*chr_count + 2);

    return _desc_str;
}

// whether host does safe-eject
static bool ejected = false;

// Some MCU doesn't have enough 8KB SRAM to store the whole disk
// We will use Flash as read-only disk with board that has
// CFG_EXAMPLE_MSC_READONLY defined

#define README_CONTENTS \
"This is not the WATCHBOOT drive.\r\n\
To drag new code onto the watch, double tap the RESET button.\r\n\r\n\
Get firmware images here: https://joeycastillo.github.io/Sensor-Watch-Documentation/firmware/prebuilt.html"

enum
{
  DISK_BLOCK_NUM  = 16, // 8KB is the smallest size that windows allow to mount
  DISK_BLOCK_SIZE = 512
};

#ifdef CFG_EXAMPLE_MSC_READONLY
const
#endif
uint8_t msc_disk[DISK_BLOCK_NUM][DISK_BLOCK_SIZE] =
{
  //------------- Block0: Boot Sector -------------//
  // byte_per_sector    = DISK_BLOCK_SIZE; fat12_sector_num_16  = DISK_BLOCK_NUM;
  // sector_per_cluster = 1; reserved_sectors = 1;
  // fat_num            = 1; fat12_root_entry_num = 16;
  // sector_per_fat     = 1; sector_per_track = 1; head_num = 1; hidden_sectors = 0;
  // drive_number       = 0x80; media_type = 0xf8; extended_boot_signature = 0x29;
  // filesystem_type    = "FAT12   "; volume_serial_number = 0x1234; volume_label = "TinyUSB MSC";
  // FAT magic code at offset 510-511
  {
      0xEB, 0x3C, 0x90, 0x4D, 0x53, 0x44, 0x4F, 0x53, 0x35, 0x2E, 0x30, 0x00, 0x02, 0x01, 0x01, 0x00,
      0x01, 0x10, 0x00, 0x10, 0x00, 0xF8, 0x01, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x29, 0x34, 0x12, 0x00, 0x00, 'T' , 'i' , 'n' , 'y' , 'U' ,
      'S' , 'B' , ' ' , 'M' , 'S' , 'C' , 0x46, 0x41, 0x54, 0x31, 0x32, 0x20, 0x20, 0x20, 0x00, 0x00,

      // Zero up to 2 last bytes of FAT magic code
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x55, 0xAA
  },

  //------------- Block1: FAT12 Table -------------//
  {
      0xF8, 0xFF, 0xFF, 0xFF, 0x0F // // first 2 entries must be F8FF, third entry is cluster end of readme file
  },

  //------------- Block2: Root Directory -------------//
  {
      // first entry is volume label
      'T' , 'i' , 'n' , 'y' , 'U' , 'S' , 'B' , ' ' , 'M' , 'S' , 'C' , 0x08, 0x00, 0x00, 0x00, 0x00,
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x4F, 0x6D, 0x65, 0x43, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
      // second entry is readme file
      'R' , 'E' , 'A' , 'D' , 'M' , 'E' , ' ' , ' ' , 'T' , 'X' , 'T' , 0x20, 0x00, 0xC6, 0x52, 0x6D,
      0x65, 0x43, 0x65, 0x43, 0x00, 0x00, 0x88, 0x6D, 0x65, 0x43, 0x02, 0x00,
      sizeof(README_CONTENTS)-1, 0x00, 0x00, 0x00 // readme's files size (4 Bytes)
  },

  //------------- Block3: Readme Content -------------//
  README_CONTENTS
};

// Invoked when received SCSI_CMD_INQUIRY
// Application fill vendor id, product id and revision with string up to 8, 16, 4 characters respectively
void tud_msc_inquiry_cb(uint8_t lun, uint8_t vendor_id[8], uint8_t product_id[16], uint8_t product_rev[4])
{
  (void) lun;

  const char vid[] = "Sensor Watch";
  const char pid[] = "Tiny Storage";
  const char rev[] = "1.0";

  memcpy(vendor_id  , vid, strlen(vid));
  memcpy(product_id , pid, strlen(pid));
  memcpy(product_rev, rev, strlen(rev));
}

// Invoked when received Test Unit Ready command.
// return true allowing host to read/write this LUN e.g SD card inserted
bool tud_msc_test_unit_ready_cb(uint8_t lun)
{
  (void) lun;

  // RAM disk is ready until ejected
  if (ejected) {
    // Additional Sense 3A-00 is NOT_FOUND
    tud_msc_set_sense(lun, SCSI_SENSE_NOT_READY, 0x3a, 0x00);
    return false;
  }

  return true;
}

// Invoked when received SCSI_CMD_READ_CAPACITY_10 and SCSI_CMD_READ_FORMAT_CAPACITY to determine the disk size
// Application update block count and block size
void tud_msc_capacity_cb(uint8_t lun, uint32_t* block_count, uint16_t* block_size)
{
  (void) lun;

  *block_count = DISK_BLOCK_NUM;
  *block_size  = DISK_BLOCK_SIZE;
}

// Invoked when received Start Stop Unit command
// - Start = 0 : stopped power mode, if load_eject = 1 : unload disk storage
// - Start = 1 : active mode, if load_eject = 1 : load disk storage
bool tud_msc_start_stop_cb(uint8_t lun, uint8_t power_condition, bool start, bool load_eject)
{
  (void) lun;
  (void) power_condition;

  if ( load_eject )
  {
    if (start)
    {
      // load disk storage
    }else
    {
      // unload disk storage
      ejected = true;
    }
  }

  return true;
}

// Callback invoked when received READ10 command.
// Copy disk's data to buffer (up to bufsize) and return number of copied bytes.
int32_t tud_msc_read10_cb(uint8_t lun, uint32_t lba, uint32_t offset, void* buffer, uint32_t bufsize)
{
  (void) lun;

  // out of ramdisk
  if ( lba >= DISK_BLOCK_NUM ) return -1;

  uint8_t const* addr = msc_disk[lba] + offset;
  memcpy(buffer, addr, bufsize);

  return (int32_t) bufsize;
}

bool tud_msc_is_writable_cb (uint8_t lun)
{
  (void) lun;

#ifdef CFG_EXAMPLE_MSC_READONLY
  return false;
#else
  return true;
#endif
}

// Callback invoked when received WRITE10 command.
// Process data in buffer to disk's storage and return number of written bytes
int32_t tud_msc_write10_cb(uint8_t lun, uint32_t lba, uint32_t offset, uint8_t* buffer, uint32_t bufsize)
{
  (void) lun;

  // out of ramdisk
  if ( lba >= DISK_BLOCK_NUM ) return -1;

#ifndef CFG_EXAMPLE_MSC_READONLY
  uint8_t* addr = msc_disk[lba] + offset;
  memcpy(addr, buffer, bufsize);
#else
  (void) lba; (void) offset; (void) buffer;
#endif

  return (int32_t) bufsize;
}

// Callback invoked when received an SCSI command not in built-in list below
// - READ_CAPACITY10, READ_FORMAT_CAPACITY, INQUIRY, MODE_SENSE6, REQUEST_SENSE
// - READ10 and WRITE10 has their own callbacks
int32_t tud_msc_scsi_cb (uint8_t lun, uint8_t const scsi_cmd[16], void* buffer, uint16_t bufsize)
{
  // read10 & write10 has their own callback and MUST not be handled here

  void const* response = NULL;
  int32_t resplen = 0;

  // most scsi handled is input
  bool in_xfer = true;

  switch (scsi_cmd[0])
  {
    default:
      // Set Sense = Invalid Command Operation
      tud_msc_set_sense(lun, SCSI_SENSE_ILLEGAL_REQUEST, 0x20, 0x00);

      // negative means error -> tinyusb could stall and/or response with failed status
      resplen = -1;
    break;
  }

  // return resplen must not larger than bufsize
  if ( resplen > bufsize ) resplen = bufsize;

  if ( response && (resplen > 0) )
  {
    if(in_xfer)
    {
      memcpy(buffer, response, (size_t) resplen);
    }else
    {
      // SCSI output
    }
  }

  return (int32_t) resplen;
}