MSC Device

This section mainly demonstrates USB mass storage device functionality. By default, RAM is used as storage medium to simulate a USB drive.

• Implement read/write and capacity acquisition interfaces for the USB drive. Note that the capacity block_num is virtual - there aren’t actually that many blocks. Read/write data exceeding BLOCK_COUNT will be discarded.

block_size is generally 512/2048/4096.

void usbd_msc_get_cap(uint8_t busid, uint8_t lun, uint32_t *block_num, uint32_t *block_size)
{
    *block_num = 1000; //Pretend having so many buffer,not has actually.
    *block_size = BLOCK_SIZE;
}
int usbd_msc_sector_read(uint8_t busid, uint8_t lun, uint32_t sector, uint8_t *buffer, uint32_t length)
{
    if (sector < BLOCK_COUNT)
        memcpy(buffer, mass_block[sector].BlockSpace, length);
    return 0;
}

int usbd_msc_sector_write(uint8_t busid, uint8_t lun, uint32_t sector, uint8_t *buffer, uint32_t length)
{
    if (sector < BLOCK_COUNT)
        memcpy(mass_block[sector].BlockSpace, buffer, length);
    return 0;
}

• By default, the above APIs execute in interrupt context. If you need to execute in non-interrupt context, you can choose the following:

1. In bare metal, enable CONFIG_USBDEV_MSC_POLLING and call usbd_msc_polling in while1, then read/write functions execute in while1.

2. In OS, enable CONFIG_USBDEV_MSC_THREAD, then read/write functions execute in thread.

• Modifying CONFIG_USBDEV_MSC_BUFSIZE will affect U disk read/write speed. It must be an integer multiple of block_size, of course, it will also increase RAM usage.

• If RAM example works but doesn’t work after changing medium to SD or FLASH, it must be a medium driver problem.