cores/usb: Add special buffer descriptor mode for control endpoint

In this mode, buffer index 0 is used for OUT transactions and
buffer index 1 is used for SETUP transactions.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

cores/usb/doc/mem-map.md

@@ -60,13 +60,16 @@ EP Status
 ,--------------------------------------------------------------,
 | f | e | d | c | b | a | 9 | 8| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
 |--------------------------------------------------------------|
-|                                      | d | b | m |  EP type  |
+|                              | t | b |  bdm  |   |  EP type  |
 '--------------------------------------------------------------'
 ```
 
-  * `d`: Data Toggle (if relevant for EP type)
+  * `t`: Data Toggle (if relevant for EP type)
   * `b`: Buffer Descriptor index
-  * `m`: Dual buffer endpoint
+  * 'bdm': Buffer descriptor mode
+    - `00` - Single Buffer (index 0 only)
+    - `01` - Double Buffer
+    - `10` - Special Control EP mode (index 0=data, 1=setup)
   * EP Type: (`h` indicates if this EP is halted)
     - `000`: Non-existant
     - `001`: Isochronous

cores/usb/rtl/usb_trans.v

@@ -133,7 +133,8 @@ module usb_trans (
 	reg        trans_dir;
 
 	reg  [2:0] ep_type;
-	reg        ep_dual_buf;
+	reg        ep_bd_dual;
+	reg        ep_bd_ctrl;
 	reg        ep_bd_idx_cur;
 	reg        ep_bd_idx_nxt;
 	reg        ep_data_toggle;
@@ -357,7 +358,7 @@ module usb_trans (
 
 	assign eps_wrdata_0 = epfw_state[1] ?
 		{ bd_state, trans_is_setup, 2'b00, xfer_length[9:0] } :
-		{ 10'h000, ep_data_toggle, ep_bd_idx_nxt, ep_dual_buf, ep_type };
+		{ 8'h00, ep_data_toggle, ep_bd_idx_nxt, ep_bd_ctrl, ep_bd_dual, 1'b0, ep_type };
 
 		// Delay line for what to expect on read data
 	always @(posedge clk or posedge rst)
@@ -376,13 +377,14 @@ module usb_trans (
 		// EP Status
 		if (epfw_cap_dl[1:0] == 2'b01) begin
 			ep_type        <= eps_rddata_3[2:0];
-			ep_dual_buf    <= eps_rddata_3[3];
-			ep_bd_idx_cur  <= eps_rddata_3[4];
-			ep_bd_idx_nxt  <= eps_rddata_3[4];
-			ep_data_toggle <= eps_rddata_3[5] & ~trans_is_setup; /* For SETUP, DT == 0 */
+			ep_bd_dual     <= eps_rddata_3[4];
+			ep_bd_ctrl     <= eps_rddata_3[5];
+			ep_bd_idx_cur  <= eps_rddata_3[5] ? trans_is_setup : eps_rddata_3[6];
+			ep_bd_idx_nxt  <= eps_rddata_3[6];
+			ep_data_toggle <= eps_rddata_3[7] & ~trans_is_setup; /* For SETUP, DT == 0 */
 		end else begin
 			ep_data_toggle <= ep_data_toggle ^ (mc_op_ep & mc_opcode[0]);
-			ep_bd_idx_nxt  <= ep_bd_idx_nxt  ^ (mc_op_ep & mc_opcode[1] & ep_dual_buf );
+			ep_bd_idx_nxt  <= ep_bd_idx_nxt  ^ (mc_op_ep & mc_opcode[1] & ep_bd_dual );
 		end
 
 		// BD Word 0