I'm writing for stm32f417 MCU. The project is generated using STM32CubeMX with firmware package: STM32Cube FW_F4 V1.26.2 (the latest so far).
In the USB Host Library there is a file related to HID class:
<my_proj_path>\Middlewares\ST\STM32_USB_Host_Library\Class\HID\Src\usbh_hid_parser.c
There is a function:
uint32_t HID_ReadItem(HID_Report_ItemTypedef *ri, uint8_t ndx)
It parses items of incoming reports. And there is a code in it:
/* read data bytes in little endian order */
for (x = 0U; x < ((ri->size & 0x7U) ? (ri->size / 8U) + 1U : (ri->size / 8U)); x++)
{
val = (uint32_t)((uint32_t)(*data) << (x * 8U));
}
val = (val >> shift) & ((1U << ri->size) - 1U);
You can see here the multiple type casting. It's just meaningless overhead. But if you iterate through the loop assigning a value to the variable val it'll be overwritten on every iteration. Moreover the data pointer also stays unchanged during the loop.
At least this line should be changed to:
val |= (uint32_t)(*data++) << (x * 8U);
I also suggest you to test this function over different size and shift values (not only <= 😎
WBR
