Jei naudojamas STM32 čipas palaiko USB HOST režimą, tai prijungti USB įrenginį labai paprasta. Mano hardwarė labai paprasta- čipas ir dvi USB jungtys. Viena jungtis suprogramuota kaip virtualus COM portas skirta peržiūrėti rezultatus, o kita USB jungtis tai USB host. Čia galima prijungti pelę ir klavietūrą. Kiti HID įrenginiai nepalaikomi.
Primenu, kad HID klavietūra palaiko iki 6 klavišų nuspaudimus (neįskaitant modifikatorius: shift, control, alt…) ir atskirai siunčiami klavišų paspaudimai ir atleidimai.
Kad viskas veiktu, tereikia savo programoje pasirašyti callbacką:

void USBH_HID_EventCallback(USBH_HandleTypeDef *phost)
{
char txt_buf[100];
char t[4];
 
strcpy(t,"[x]");
	if(USBH_HID_GetDeviceType(phost) == HID_MOUSE)  // if the HID is Mouse
	{
		HID_MOUSE_Info_TypeDef *Mouse_Info;
		Mouse_Info = USBH_HID_GetMouseInfo(phost);  // Get the info
		int8_t dX_Val = Mouse_Info->x;  // get the delta x value (note unsigned - signed conversion)
		int8_t dY_Val = Mouse_Info->y;  // get the delta y value
 
		int len = sprintf (txt_buf, "dX=%d, dY=%d, Button1=%d, Button2=%d, Button3=%d\r\n", dX_Val, dY_Val, Mouse_Info->buttons[0],Mouse_Info->buttons[1], Mouse_Info->buttons[2]);
		user_usb_tx((uint8_t *) txt_buf,len);
	}
	if(USBH_HID_GetDeviceType(phost) == HID_KEYBOARD)
	{
 
		HID_KEYBD_Info_TypeDef *Keyboard_Info;
		Keyboard_Info = USBH_HID_GetKeybdInfo(phost);  // get the info
		txt_buf[0]=0;
		unsigned char i;
		for(i=0;i<6;i++)
		{
		if(Keyboard_Info->keys[i] != OLDKEYS[i] )
			{
				if (Keyboard_Info->keys[i]==0) {strcat(txt_buf,"UPKEY:"); hex8(txt_buf,OLDKEYS[i]);t[1]=Scan2Char(OLDKEYS[i]); strcat(txt_buf,t);}
				else if (OLDKEYS[i]==0) {strcat(txt_buf,"DOWNKEY:"); hex8(txt_buf,Keyboard_Info->keys[i]);t[1]=Scan2Char(Keyboard_Info->keys[i]); strcat(txt_buf,t);}
				else {strcat(txt_buf,"ERR:"); hex8(txt_buf,Keyboard_Info->keys[i]); strcat(txt_buf,"-");hex8(txt_buf,OLDKEYS[i]);}
			}
			OLDKEYS[i]=Keyboard_Info->keys[i];
		}
		strcat(txt_buf,"\r\n");
		user_print_usb( txt_buf);
	}
}

Pačiam HID reporte visada transliuojami visi nuspausti klavišai, todėl, jei reikia susiderinti su PS2 ar senesniu standartu, reikia tikrinti, koks klavišas nuspaustas ir koks paleistas. Ta daro ciklas 24-33 eilutėse.
Rezultatas:

UPKEY:12[o]
DOWNKEY:13[p]
UPKEY:13[p]
DOWNKEY:2F[[]
UPKEY:2F[[]
DOWNKEY:30[]]
UPKEY:30[]]
DOWNKEY:31[\]
UPKEY:31[\]
DOWNKEY:04[q]
DOWNKEY:16[s]
DOWNKEY:07[d]
DOWNKEY:09[f]


DOWNKEY:2C[ ]
UPKEY:16[s]
UPKEY:07[d]
UPKEY:09[f]
UPKEY:04[q]
UPKEY:2C[ ]
DOWNKEY:0B[h]
UPKEY:0B[h]

Visas demo softo source code čia: STM32CubeMX USB host HID demo source code.