diff --git a/litedram/frontend/bist.py b/litedram/frontend/bist.py
index 8568e73..19623ca 100644
--- a/litedram/frontend/bist.py
+++ b/litedram/frontend/bist.py
@@ -4,14 +4,15 @@ from functools import reduce
 from operator import xor
 
 from migen import *
-from migen.genlib.cdc import PulseSynchronizer, BusSynchronizer
+from migen.genlib.cdc import MultiReg
+from migen.genlib.cdc import PulseSynchronizer
+from migen.genlib.cdc import BusSynchronizer
 
 from litex.soc.interconnect.csr import *
 
 from litedram.frontend.dma import LiteDRAMDMAWriter, LiteDRAMDMAReader
 
 
-@CEInserter()
 class LFSR(Module):
     """Linear-Feedback Shift Register to generate a pseudo-random sequence.
 
@@ -26,10 +27,10 @@ class LFSR(Module):
 
     Attributes
     ----------
-    o : in
+    o : out
         Output data
     """
-    def __init__(self, n_out, n_state=31, taps=[27, 30]):
+    def __init__(self, n_out, n_state, taps):
         self.o = Signal(n_out)
 
         # # #
@@ -48,7 +49,6 @@ class LFSR(Module):
         ]
 
 
-@CEInserter()
 class Counter(Module):
     """Simple incremental counter.
 
@@ -59,7 +59,7 @@ class Counter(Module):
 
     Attributes
     ----------
-    o : in
+    o : out
         Output data
     """
     def __init__(self, n_out):
@@ -70,23 +70,69 @@ class Counter(Module):
         self.sync += self.o.eq(self.o + 1)
 
 
+@CEInserter()
+class Generator(Module):
+    """Address/Data Generator.
+
+    Parameters
+    ----------
+    n_out : int
+        Width of the output data signal.
+
+    Attributes
+    ----------
+    random_enable : in
+        Enable Random (LFSR)
+
+    o : out
+        Output data
+    """
+    def __init__(self, n_out, n_state, taps):
+        self.random_enable = Signal()
+        self.o = Signal(n_out)
+
+        # # #
+
+        lfsr = LFSR(n_out, n_state, taps)
+        count = Counter(n_out)
+        self.submodules += lfsr, count
+
+        self.comb += \
+            If(self.random_enable,
+                self.o.eq(lfsr.o)
+            ).Else(
+                self.o.eq(count.o)
+            )
+
+
 @ResetInserter()
 class _LiteDRAMBISTGenerator(Module):
-    def __init__(self, dram_port, random):
+    def __init__(self, dram_port):
         ashift = log2_int(dram_port.dw//8)
         awidth = dram_port.aw + ashift
         self.start = Signal()
         self.done = Signal()
         self.base = Signal(awidth)
         self.length = Signal(awidth)
+        self.random_data_enable = Signal()
+        self.random_addr_enable = Signal()
         self.ticks = Signal(32)
 
         # # #
 
-        gen_cls = LFSR if random else Counter
-        gen = gen_cls(min(dram_port.dw, 32)) # FIXME: remove lfsr limitation
+        # data / address generators
+        data_gen = Generator(31, n_state=31, taps=[27, 30]) # PRBS31
+        addr_gen = Generator(23, n_state=23, taps=[17, 22]) # PRBS23
+        assert (23 + ashift) < awidth # addressing large enough for random
+        self.submodules += data_gen, addr_gen
+        self.comb += [
+            data_gen.random_enable.eq(self.random_data_enable),
+            addr_gen.random_enable.eq(self.random_addr_enable)
+        ]
+
+        # dma
         dma = LiteDRAMDMAWriter(dram_port)
-        self.submodules += dma, gen
+        self.submodules += dma
 
         cmd_counter = Signal(dram_port.aw, reset_less=True)
 
@@ -102,7 +148,8 @@ class _LiteDRAMBISTGenerator(Module):
         fsm.act("RUN",
             dma.sink.valid.eq(1),
             If(dma.sink.ready,
-                gen.ce.eq(1),
+                data_gen.ce.eq(1),
+                addr_gen.ce.eq(1),
                 NextValue(cmd_counter, cmd_counter + 1),
                 If(cmd_counter == (self.length[ashift:] - 1),
                     NextState("DONE")
@@ -114,8 +161,8 @@ class _LiteDRAMBISTGenerator(Module):
             self.done.eq(1)
         )
         self.comb += [
-            dma.sink.address.eq(self.base[ashift:] + cmd_counter),
-            dma.sink.data.eq(gen.o)
+            dma.sink.address.eq(self.base[ashift:] + addr_gen.o),
+            dma.sink.data.eq(data_gen.o)
         ]
 
 
@@ -126,21 +173,29 @@ class LiteDRAMBISTGenerator(Module, AutoCSR):
     ----------
     reset : in
         Reset the module.
+
     start : in
         Start the generation.
 
-    base : in
-        DRAM address to start from.
-    length : in
-        Number of DRAM words to write.
-
     done : out
         The module has completed writing the pattern.
 
+    base : in
+        DRAM address to start from.
+
+    length : in
+        Number of DRAM words to write.
+
+    random_data_enable : in
+        Enable random data (LFSR)
+
+    random_addr_enable : in
+        Enable random addressing (LFSR)
+
     ticks : out
         Duration of the generation.
     """
-    def __init__(self, dram_port, random=True):
+    def __init__(self, dram_port):
         ashift = log2_int(dram_port.dw//8)
         awidth = dram_port.aw + ashift
         self.reset = CSR()
@@ -148,13 +203,15 @@ class LiteDRAMBISTGenerator(Module, AutoCSR):
         self.done = CSRStatus()
         self.base = CSRStorage(awidth)
         self.length = CSRStorage(awidth)
+        self.random_data_enable = CSRStorage()
+        self.random_addr_enable = CSRStorage()
         self.ticks = CSRStatus(32)
 
         # # #
 
         cd = dram_port.cd
 
-        core = _LiteDRAMBISTGenerator(dram_port, random)
+        core = _LiteDRAMBISTGenerator(dram_port)
         core = ClockDomainsRenamer(cd)(core)
         self.submodules += core
 
@@ -187,6 +244,11 @@ class LiteDRAMBISTGenerator(Module, AutoCSR):
             core.length.eq(length_sync.o)
         ]
 
+        self.specials += [
+            MultiReg(self.random_data_enable.storage, core.random_data_enable, cd),
+            MultiReg(self.random_addr_enable.storage, core.random_addr_enable, cd),
+        ]
+
         ticks_sync = BusSynchronizer(32, cd, "sys")
         self.submodules += ticks_sync
         self.comb += [
@@ -197,22 +259,33 @@ class LiteDRAMBISTGenerator(Module, AutoCSR):
 
 @ResetInserter()
 class _LiteDRAMBISTChecker(Module, AutoCSR):
-    def __init__(self, dram_port, random):
+    def __init__(self, dram_port):
         ashift = log2_int(dram_port.dw//8)
         awidth = dram_port.aw + ashift
         self.start = Signal()
         self.done = Signal()
         self.base = Signal(awidth)
         self.length = Signal(awidth)
+        self.random_data_enable = Signal()
+        self.random_addr_enable = Signal()
         self.ticks = Signal(32)
         self.errors = Signal(32)
 
         # # #
 
-        gen_cls = LFSR if random else Counter
-        gen = gen_cls(min(dram_port.dw, 32)) # FIXME: remove lfsr limitation
+        # data / address generators
+        data_gen = Generator(31, n_state=31, taps=[27, 30]) # PRBS31
+        addr_gen = Generator(23, n_state=23, taps=[17, 22]) # PRBS23
+        assert (23 + ashift) < awidth # addressing large enough for random
+        self.submodules += data_gen, addr_gen
+        self.comb += [
+            data_gen.random_enable.eq(self.random_data_enable),
+            addr_gen.random_enable.eq(self.random_addr_enable)
+        ]
+
+        # dma
         dma = LiteDRAMDMAReader(dram_port)
-        self.submodules += dma, gen
+        self.submodules += dma
 
         # address
         cmd_counter = Signal(dram_port.aw, reset_less=True)
@@ -228,6 +301,7 @@ class _LiteDRAMBISTChecker(Module, AutoCSR):
         cmd_fsm.act("RUN",
             dma.sink.valid.eq(1),
             If(dma.sink.ready,
+                addr_gen.ce.eq(1),
                 NextValue(cmd_counter, cmd_counter + 1),
                 If(cmd_counter == (self.length[ashift:] - 1),
                     NextState("DONE")
@@ -235,7 +309,7 @@ class _LiteDRAMBISTChecker(Module, AutoCSR):
             )
         )
         cmd_fsm.act("DONE")
-        self.comb += dma.sink.address.eq(self.base[ashift:] + cmd_counter)
+        self.comb += dma.sink.address.eq(self.base[ashift:] + addr_gen.o)
 
         # data
         data_counter = Signal(dram_port.aw, reset_less=True)
@@ -253,9 +327,9 @@ class _LiteDRAMBISTChecker(Module, AutoCSR):
         data_fsm.act("RUN",
             dma.source.ready.eq(1),
             If(dma.source.valid,
-                gen.ce.eq(1),
+                data_gen.ce.eq(1),
                 NextValue(data_counter, data_counter + 1),
-                If(dma.source.data != gen.o,
+                If(dma.source.data != data_gen.o,
                     NextValue(self.errors, self.errors + 1)
                 ),
                 If(data_counter == (self.length[ashift:] - 1),
@@ -279,13 +353,19 @@ class LiteDRAMBISTChecker(Module, AutoCSR):
     start : in
         Start the checking
 
+    done : out
+        The module has completed checking
+
     base : in
         DRAM address to start from.
     length : in
         Number of DRAM words to check.
 
-    done : out
-        The module has completed checking
+    random_data_enable : in
+        Enable random data (LFSR)
+
+    random_addr_enable : in
+        Enable random addressing (LFSR)
 
     ticks: out
         Duration of the check.
@@ -293,14 +373,16 @@ class LiteDRAMBISTChecker(Module, AutoCSR):
     errors : out
         Number of DRAM words which don't match.
     """
-    def __init__(self, dram_port, random=True):
+    def __init__(self, dram_port):
         ashift = log2_int(dram_port.dw//8)
         awidth = dram_port.aw + ashift
         self.reset = CSR()
         self.start = CSR()
+        self.done = CSRStatus()
         self.base = CSRStorage(awidth)
         self.length = CSRStorage(awidth)
-        self.done = CSRStatus()
+        self.random_data_enable = CSRStorage()
+        self.random_addr_enable = CSRStorage()
         self.ticks = CSRStatus(32)
         self.errors = CSRStatus(32)
 
@@ -308,7 +390,7 @@ class LiteDRAMBISTChecker(Module, AutoCSR):
 
         cd = dram_port.cd
 
-        core = _LiteDRAMBISTChecker(dram_port, random)
+        core = _LiteDRAMBISTChecker(dram_port)
         core = ClockDomainsRenamer(cd)(core)
         self.submodules += core
 
@@ -341,6 +423,11 @@ class LiteDRAMBISTChecker(Module, AutoCSR):
             core.length.eq(length_sync.o)
         ]
 
+        self.specials += [
+            MultiReg(self.random_data_enable.storage, core.random_data_enable, cd),
+            MultiReg(self.random_addr_enable.storage, core.random_addr_enable, cd),
+        ]
+
         ticks_sync = BusSynchronizer(32, cd, "sys")
         self.submodules += ticks_sync
         self.comb += [