diff --git a/lib/axis/rtl/axis_ram_switch.v b/lib/axis/rtl/axis_ram_switch.v
index d79cfb9f1..7a2be8e1d 100644
--- a/lib/axis/rtl/axis_ram_switch.v
+++ b/lib/axis/rtl/axis_ram_switch.v
@@ -922,7 +922,7 @@ generate
             end
 
             // process commands and issue memory reads
-            if (cmd_valid_reg && (!ram_rd_en_reg || ram_rd_ack) && ($unsigned(out_fifo_ctrl_wr_ptr_reg - out_fifo_rd_ptr_reg) < 32)) begin
+            if (cmd_valid_reg && !cmd_status_valid_next && (!ram_rd_en_reg || ram_rd_ack) && ($unsigned(out_fifo_ctrl_wr_ptr_reg - out_fifo_rd_ptr_reg) < 32)) begin
                 // update counters
                 rd_ptr_next[ADDR_WIDTH-1:0] = rd_ptr_reg[ADDR_WIDTH-1:0] + 1;
                 len_next = len_reg - 1;
diff --git a/lib/axis/syn/axis_async_fifo.sdc b/lib/axis/syn/axis_async_fifo.sdc
new file mode 100644
index 000000000..e3a569a4f
--- /dev/null
+++ b/lib/axis/syn/axis_async_fifo.sdc
@@ -0,0 +1,51 @@
+# Copyright (c) 2020 Alex Forencich
+# 
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+# 
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+# 
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+# AXI stream asynchronous FIFO timing constraints
+
+proc constrain_axis_async_fifo_inst { inst } {
+    puts "Inserting timing constraints for axis_async_fifo instance $inst"
+
+    # reset synchronization
+    set_false_path -from * -to [get_registers "$inst|s_rst_sync*_reg $inst|m_rst_sync*_reg"]
+
+    if {[get_collection_size [get_registers -nowarn "$inst|s_rst_sync2_reg"]]} {
+        set_max_delay  -from [get_registers "$inst|s_rst_sync2_reg"] -to [get_registers "$inst|s_rst_sync3_reg"] 8.000
+    }
+
+    if {[get_collection_size [get_registers -nowarn "$inst|m_rst_sync2_reg"]]} {
+        set_max_delay  -from [get_registers "$inst|m_rst_sync2_reg"] -to [get_registers "$inst|m_rst_sync3_reg"] 8.000
+    }
+
+    # pointer synchronization
+    set_max_delay -from [get_registers "$inst|rd_ptr_reg[*] $inst|rd_ptr_gray_reg[*]"] -to [get_registers "$inst|rd_ptr_gray_sync1_reg[*]"] 8.000
+    set_max_delay -from [get_registers "$inst|wr_ptr_reg[*] $inst|wr_ptr_gray_reg[*] $inst|wr_ptr_sync_gray_reg[*]"] -to [get_registers "$inst|wr_ptr_gray_sync1_reg[*]"] 8.000
+
+    # frame FIFO pointer update synchronization
+    set_max_delay -from [get_registers "$inst|wr_ptr_update_reg"] -to [get_registers "$inst|wr_ptr_update_sync1_reg"] 8.000
+    set_max_delay -from [get_registers "$inst|wr_ptr_update_sync3_reg"] -to [get_registers "$inst|wr_ptr_update_ack_sync1_reg"] 8.000
+
+    # status synchronization
+    foreach i {overflow bad_frame good_frame} {
+        if {[get_collection_size [get_registers -nowarn "$inst|${i}_sync*_reg"]]} {
+            set_max_delay -from [get_registers "$inst|${i}_sync1_reg"] -to [get_registers "$inst|${i}_sync2_reg"] 8.000
+        }
+    }
+}
diff --git a/lib/axis/syn/sync_reset.sdc b/lib/axis/syn/sync_reset.sdc
new file mode 100644
index 000000000..fe5c6bf8b
--- /dev/null
+++ b/lib/axis/syn/sync_reset.sdc
@@ -0,0 +1,28 @@
+# Copyright (c) 2020 Alex Forencich
+# 
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+# 
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+# 
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+# reset synchronizer timing constraints
+
+proc constrain_sync_reset_inst { inst } {
+    puts "Inserting timing constraints for sync_reset instance $inst"
+
+    # reset synchronization
+    set_false_path -from * -to [get_registers "$inst|sync_reg[*]"]
+}