Merge pull request #43 from twelho/dfu-custom-alt-setting

Enable specifying the alternate setting for the DFU interface per-target

Author: devanlai

src/usb_conf.c

@@ -45,28 +45,62 @@ static const struct usb_device_descriptor dev = {
     .bNumConfigurations = 1,
 };
 
-static const struct usb_interface_descriptor dfu_iface = {
-    .bLength = USB_DT_INTERFACE_SIZE,
-    .bDescriptorType = USB_DT_INTERFACE,
-    .bInterfaceNumber = INTF_DFU,
-    .bAlternateSetting = 0,
-    .bNumEndpoints = 0,
-    .bInterfaceClass = 0xFE,
-    .bInterfaceSubClass = 1,
-    .bInterfaceProtocol = 2,
-    .iInterface = 4,
-
-    .endpoint = NULL,
-
-    .extra = &dfu_function,
-    .extralen = sizeof(dfu_function),
+// Macro to create a dummy (no-op) USB interface descriptor with the given alternate setting
+#define ALT_DUMMY(N) {                      \
+    .bLength = USB_DT_INTERFACE_SIZE,       \
+    .bDescriptorType = USB_DT_INTERFACE,    \
+    .bInterfaceNumber = INTF_DFU,           \
+    .bAlternateSetting = (N),               \
+    .bNumEndpoints = 0,                     \
+    .bInterfaceClass = 0,                   \
+    .bInterfaceSubClass = 0,                \
+    .bInterfaceProtocol = 0,                \
+    .iInterface = 0,                        \
+    .endpoint = NULL,                       \
+    .extra = NULL,                          \
+    .extralen = 0,                          \
+},
+
+// Functionality for creating repetitive ALT_DUMMY structs with an increasing count during compile time.
+// It doesn't look very nice, but C doesn't allow loops in preprocessor macros, so this needs to be hard-coded.
+#define ALT0
+#define ALT1 ALT_DUMMY(0)
+#define ALT2 ALT1 ALT_DUMMY(1)
+#define ALT3 ALT2 ALT_DUMMY(2)
+#define ALT4 ALT3 ALT_DUMMY(3)
+#define ALT5 ALT4 ALT_DUMMY(4)
+#define ALTW(n) ALT##n // Wrapper macro for expansion
+#define ALTN(n) ALTW(n)
+
+static const struct usb_interface_descriptor altsettings[] = {
+    ALTN(USB_DFU_ALTN) // Prepend USB_DFU_ALTN dummy USB interface descriptors to "pad" the real one
+    {
+        .bLength = USB_DT_INTERFACE_SIZE,
+        .bDescriptorType = USB_DT_INTERFACE,
+        .bInterfaceNumber = INTF_DFU,
+        .bAlternateSetting = USB_DFU_ALTN,
+        .bNumEndpoints = 0,
+        .bInterfaceClass = 0xFE,
+        .bInterfaceSubClass = 1,
+        .bInterfaceProtocol = 2,
+        .iInterface = 4,
+
+        .endpoint = NULL,
+
+        .extra = &dfu_function,
+        .extralen = sizeof(dfu_function),
+    }
 };
 
+// Tracking this is mandatory if exposing multiple altsettings
+static uint8_t cur_altsetting = 0;
+
 static const struct usb_interface interfaces[] = {
     /* DFU interface */
     {
-        .num_altsetting = 1,
-        .altsetting = &dfu_iface,
+        .cur_altsetting = &cur_altsetting,
+        .num_altsetting = USB_DFU_ALTN + 1,
+        .altsetting = (const struct usb_interface_descriptor*)&altsettings,
     }
 };
 

src/usb_conf.h

@@ -33,6 +33,10 @@
 #define USB_PID                 0xdb42
 #endif
 
+// The DFU interface doesn't have any special alternate setting by default
+#ifndef USB_DFU_ALTN
+#define USB_DFU_ALTN 0
+#endif
 
 #ifndef USB_PRODUCT_STRING