modules: add DDR3-800 timings for MT41J128M16 and use it on arty example

examples/arty_config.py

@@ -8,7 +8,7 @@ core_config = {
     # modules / phy
     "sdram_module": MT41K128M16,
     "sdram_module_nb": 1,
-    "sdram_module_speedgrade": "1066",
+    "sdram_module_speedgrade": "800",
     "sdram_rank_nb": 1,
     "sdram_phy": A7DDRPHY,
 

litedram/modules.py

@@ -248,6 +248,14 @@ class MT41J128M16(SDRAMModule):
     tCCD  = (4, None)
     tRRD  = 10
     # speedgrade related timings
+    # DDR3-800
+    tRP_800  = 13.1
+    tRCD_800 = 13.1
+    tWR_800  = 13.1
+    tRFC_800 = 64
+    tFAW_800 = (20, None)
+    tRC_800 = 50.625
+    tRAS_800 = 37.5
     # DDR3-1066
     tRP_1066  = 13.1
     tRCD_1066 = 13.1