common/DQSPattern: add transmission order, minor simplification on USDDRPHY.

litedram/common.py

@@ -156,6 +156,8 @@ class DQSPattern(Module):
 
         # # #
 
+        # DQS Pattern transmitted as LSB-first.
+
         self.comb += [
             self.o.eq(0b01010101),
             If(self.preamble,

litedram/phy/usddrphy.py

@@ -267,7 +267,7 @@ class USDDRPHY(Module, AutoCSR):
                         i_CLK    = ClockSignal("sys4x"),
                         i_CLKDIV = ClockSignal(),
                         i_T      = ~dqs_oe_delay.output,
-                        i_D      = Cat(*[dqs_pattern.o[n] for n in range(8)]),
+                        i_D      = dqs_pattern.o,
                         o_OQ     = dqs_nodelay,
                         o_T_OUT  = dqs_t,