commit 81593c44881809b44ac4f8958b85031039ef7862
author Adrian Lees <a.lees@lowrisc.org> Fri Feb 17 23:18:02 2023 +0000
committer Pirmin Vogel <vogelpi@lowrisc.org> Thu Feb 23 11:58:54 2023 +0100
tree 1b2ff9c9a5bdc824262acc3ada070c787714b221
parent d8df1b394a7bcb8c4d2ae60455ced043889b607e

[usbdev] Fix pinflip logic

Fix implementation of pinflip on both input and output paths;
inverting the signals is not the same as exchanging them
because the two differential signals are not always opposing.

Signed-off-by: Adrian Lees <a.lees@lowrisc.org>

hw/ip/usbdev/rtl/usb_fs_rx.sv

diff --git a/hw/ip/usbdev/rtl/usb_fs_rx.sv b/hw/ip/usbdev/rtl/usb_fs_rx.sv
index 35b095e..10bea5c 100644
--- a/hw/ip/usbdev/rtl/usb_fs_rx.sv
+++ b/hw/ip/usbdev/rtl/usb_fs_rx.sv
@@ -65,8 +65,8 @@
   //////////////////////
   // Adjust inputs when D+/D- are flipped on the USB side
   logic usb_dp_flipped, usb_dn_flipped, usb_d_flipped;
-  assign usb_dp_flipped = usb_dp_i ^ cfg_pinflip_i;
-  assign usb_dn_flipped = usb_dn_i ^ cfg_pinflip_i;
+  assign usb_dp_flipped = cfg_pinflip_i ? usb_dn_i : usb_dp_i;
+  assign usb_dn_flipped = cfg_pinflip_i ? usb_dp_i : usb_dn_i;
   assign usb_d_flipped = usb_d_i ^ cfg_pinflip_i;
 
   ///////////////////////////////////////

hw/ip/usbdev/rtl/usb_fs_tx.sv

diff --git a/hw/ip/usbdev/rtl/usb_fs_tx.sv b/hw/ip/usbdev/rtl/usb_fs_tx.sv
index fa28ea1..517b8f8 100644
--- a/hw/ip/usbdev/rtl/usb_fs_tx.sv
+++ b/hw/ip/usbdev/rtl/usb_fs_tx.sv
@@ -453,19 +453,17 @@
 
   // Handle the D+ / D- pin flip on the USB side, and provide both the
   // dp/dn and d/se0 interfaces, for compatibility with multiple driver types.
-  logic usb_d_flipped, usb_se0_flipped, usb_dp_flipped, usb_dn_flipped;
+  logic usb_se0_flipped, usb_dp_flipped, usb_dn_flipped;
 
   always_comb begin
     if (link_reset_i) begin
-      usb_d_flipped = 1'b0 ^ cfg_pinflip_i;
       usb_se0_flipped = 1'b0;
       usb_dp_flipped = 1'b0 ^ cfg_pinflip_i;
       usb_dn_flipped = 1'b1 ^ cfg_pinflip_i;
     end else begin
-      usb_d_flipped = usb_d_d ^ cfg_pinflip_i;
       usb_se0_flipped = usb_se0_d;
-      usb_dp_flipped = (usb_d_d & ~usb_se0_d) ^ cfg_pinflip_i;
-      usb_dn_flipped = (~usb_d_d & ~usb_se0_d) ^ cfg_pinflip_i;
+      usb_dp_flipped = (cfg_pinflip_i ? ~usb_d_d :  usb_d_d) & ~usb_se0_d;
+      usb_dn_flipped = (cfg_pinflip_i ?  usb_d_d : ~usb_d_d) & ~usb_se0_d;
     end
   end
 
@@ -475,7 +473,7 @@
   ) u_usb_d_o_flop (
     .clk_i,
     .rst_ni,
-    .d_i(usb_d_flipped),
+    .d_i(usb_dp_flipped),  // Note: single-ended 'D' output mirrors D+
     .q_o(usb_d_o)
   );