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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.
.. code-block:: C
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.
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