stmhal: Implement SNAK/CNAK mechanism for USB HID receive.

This implements flow control in case user does not call recv method often
enough (it tells host side to stop sending more data).

stmhal/usbd_hid_interface.c

@@ -89,7 +89,8 @@ static int8_t HID_Itf_Receive(uint8_t* Buf, uint32_t Len) {
     // initiate next USB packet transfer, to append to existing data in buffer
     USBD_HID_SetRxBuffer(&hUSBDDevice, buffer[current_write_buffer]);
     USBD_HID_ReceivePacket(&hUSBDDevice);
-
+    // Set NAK to indicate we need to process read buffer
+    USBD_HID_SetNAK(&hUSBDDevice);
     return USBD_OK;
 }
 
@@ -125,6 +126,9 @@ int USBD_HID_Rx(uint8_t *buf, uint32_t len, uint32_t timeout) {
     memcpy(buf, buffer[current_read_buffer], last_read_len);
     current_read_buffer = !current_read_buffer;
 
+    // Clear NAK to indicate we are ready to read more data
+    USBD_HID_ClearNAK(&hUSBDDevice);
+
     // Success, return number of bytes read
     return last_read_len;
 }

stmhal/usbdev/class/inc/usbd_cdc_msc_hid.h

@@ -116,5 +116,7 @@ uint8_t USBD_HID_SetRxBuffer(USBD_HandleTypeDef *pdev, uint8_t *pbuff);
 uint8_t USBD_HID_ReceivePacket(USBD_HandleTypeDef *pdev);
 int USBD_HID_CanSendReport(USBD_HandleTypeDef *pdev);
 uint8_t USBD_HID_SendReport(USBD_HandleTypeDef *pdev, uint8_t *report, uint16_t len);
+uint8_t USBD_HID_SetNAK(USBD_HandleTypeDef *pdev);
+uint8_t USBD_HID_ClearNAK(USBD_HandleTypeDef *pdev);
 
 #endif // _USB_CDC_MSC_CORE_H_

stmhal/usbdev/class/src/usbd_cdc_msc_hid.c

@@ -1093,6 +1093,24 @@ uint8_t USBD_HID_SendReport(USBD_HandleTypeDef *pdev, uint8_t *report, uint16_t
     return USBD_OK;
 }
 
+uint8_t USBD_HID_SetNAK(USBD_HandleTypeDef *pdev) {
+    // get USBx object from pdev (needed for USBx_OUTEP macro below)
+    PCD_HandleTypeDef *hpcd = pdev->pData;
+    USB_OTG_GlobalTypeDef *USBx = hpcd->Instance;
+    // set NAK on HID OUT endpoint
+    USBx_OUTEP(HID_OUT_EP_WITH_CDC)->DOEPCTL |= USB_OTG_DOEPCTL_SNAK;
+    return USBD_OK;
+}
+
+uint8_t USBD_HID_ClearNAK(USBD_HandleTypeDef *pdev) {
+    // get USBx object from pdev (needed for USBx_OUTEP macro below)
+    PCD_HandleTypeDef *hpcd = pdev->pData;
+    USB_OTG_GlobalTypeDef *USBx = hpcd->Instance;
+    // clear NAK on HID OUT endpoint
+    USBx_OUTEP(HID_OUT_EP_WITH_CDC)->DOEPCTL |= USB_OTG_DOEPCTL_CNAK;
+    return USBD_OK;
+}
+
 // CDC/MSC/HID interface class callback structure
 USBD_ClassTypeDef USBD_CDC_MSC_HID = {
     USBD_CDC_MSC_HID_Init,