diff --git a/README.md b/README.md
index 923e947..4588d4d 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,12 @@ Ongoing experiments with the Cologne Chip's GateMate FPGA architecture. All expe
 
 Simple design which should display a blinking LED waving from LED1-LED8 of the GateMate FPGA Starter Kit. It uses *CC_PLL* & *CC_CFG_END* primitives of the GateMate FPGA.
 
+### uart_loop
+
+Simple UART loop with UART RX & TX units and FIFO buffer between. It uses *CC_PLL* & *CC_CFG_END* primitives of the GateMate FPGA. With fifo depth >= 18 Yosys is infering *CC_BRAM_20K* instead of registers.
+
+Beware: The simulation model of *CC_BRAM_20K* seems to be incorrect, so better set fifo depth < 18 or use yosys option `-nobram` when synthesizing the model for post-synthesis & post-implementation simulation.
+
 ### uart_reg
 
 Register file which can be accessed through UART. It uses *CC_PLL* & *CC_CFG_END* primitives of the GateMate FPGA. It contains 8 registers storing values of one byte each. The first received byte on the axis in port contains command & address:
diff --git a/uart_loop/rtl/uart_loop.vhd b/uart_loop/rtl/uart_loop.vhd
index e03c3c8..ce149db 100644
--- a/uart_loop/rtl/uart_loop.vhd
+++ b/uart_loop/rtl/uart_loop.vhd
@@ -1,8 +1,5 @@
--- This design implements a register file which can
--- be accessed by an UART with 9600 baud
---
--- See into uart_ctrl.vhd for documentation of the protocol
--- used to read / write the register file.
+-- Simple UART loop with UART RX & TX units and FIFO buffer
+-- between. It's working at baudrate 9600.
 
 
 library ieee ;
@@ -44,7 +41,7 @@ begin
   pll : CC_PLL
   generic map (
     REF_CLK => "10",
-    OUT_CLK => "1",
+    OUT_CLK => "10",
     PERF_MD => "ECONOMY"
   )
   port map (
@@ -68,7 +65,7 @@ begin
 
   uart_rx : entity work.uart_rx
   generic map (
-    CLK_DIV => 104
+    CLK_DIV => 1040
   )
   port map (
     -- globals
@@ -84,7 +81,7 @@ begin
 
   axis_fifo : entity work.axis_fifo
   generic map (
-    DEPTH => 64,
+    DEPTH => 16,
     WIDTH => 8
   )
   port map (
@@ -107,7 +104,7 @@ begin
 
   uart_tx : entity work.uart_tx
   generic map (
-    CLK_DIV => 104
+    CLK_DIV => 1040
   )
   port map (
     -- globals
diff --git a/uart_loop/sim/Makefile b/uart_loop/sim/Makefile
index b280847..1e439fb 100644
--- a/uart_loop/sim/Makefile
+++ b/uart_loop/sim/Makefile
@@ -20,7 +20,7 @@ tb_${DESIGN_NAME}: ${LIB_SRC} ${RTL_SRC} ${SIM_SRC}
 
 sim: tb_${DESIGN_NAME}
 	@echo "Run testbench ..."
-	ghdl -r ${SIM_FLAGS} -Pwork tb_${DESIGN_NAME} --assert-level=error
+	ghdl -r ${SIM_FLAGS} -Pwork tb_${DESIGN_NAME} --assert-level=error --wave=tb_${DESIGN_NAME}.ghw
 
 work:
 	mkdir $@
diff --git a/uart_loop/syn/Makefile b/uart_loop/syn/Makefile
index 6bfb630..3e44100 100644
--- a/uart_loop/syn/Makefile
+++ b/uart_loop/syn/Makefile
@@ -2,7 +2,7 @@ DESIGN_NAME := uart_loop
 WORK_FILES  := ../../lib/user_components.vhd ../rtl/uart_tx.vhd ../rtl/uart_rx.vhd ../rtl/${DESIGN_NAME}.vhd
 GM_FILES    := ../../lib/rtl_components.vhd
 GHDL_FLAGS  := --std=08 --workdir=build -Pbuild
-YOSYSPIPE   := -nomx8 -retime -nobram
+YOSYSPIPE   := -nomx8 -retime
 # ATTENTION: -luttree option seems to mis-synthesize the design, broken with synth_gatemate?
 PNRFLAGS    := -om 2
 PNRTOOL     := $(shell which p_r)
diff --git a/uart_loop/syn/tb_uart_loop.v b/uart_loop/syn/tb_uart_loop.v
index 1016252..1d96441 100644
--- a/uart_loop/syn/tb_uart_loop.v
+++ b/uart_loop/syn/tb_uart_loop.v
@@ -18,8 +18,8 @@ module CC_PLL #(
   reg r_pll_clk;
   reg r_user_pll_locked;
 
-  // OUT_FREQ = 1 MHz
-  integer clk_half_period = 500;
+  // OUT_FREQ = 10 MHz
+  integer clk_half_period = 50;
 
   initial begin
     r_pll_clk         = 1'b0;
diff --git a/uart_reg/rtl/uart_reg.vhd b/uart_reg/rtl/uart_reg.vhd
index 89bc0b2..8d30e84 100644
--- a/uart_reg/rtl/uart_reg.vhd
+++ b/uart_reg/rtl/uart_reg.vhd
@@ -44,7 +44,7 @@ begin
   pll : CC_PLL
   generic map (
     REF_CLK => "10",
-    OUT_CLK => "1",
+    OUT_CLK => "10",
     PERF_MD => "ECONOMY"
   )
   port map (
@@ -68,7 +68,7 @@ begin
 
   uart_rx : entity work.uart_rx
   generic map (
-    CLK_DIV => 104
+    CLK_DIV => 1040
   )
   port map (
     -- globals
@@ -99,7 +99,7 @@ begin
 
   uart_tx : entity work.uart_tx
   generic map (
-    CLK_DIV => 104
+    CLK_DIV => 1040
   )
   port map (
     -- globals
diff --git a/uart_reg/syn/tb_uart_reg.v b/uart_reg/syn/tb_uart_reg.v
index 9756226..00b727e 100644
--- a/uart_reg/syn/tb_uart_reg.v
+++ b/uart_reg/syn/tb_uart_reg.v
@@ -19,7 +19,7 @@ module CC_PLL #(
   reg r_user_pll_locked;
 
   // OUT_FREQ = 1 MHz
-  integer clk_half_period = 500;
+  integer clk_half_period = 50;
 
   initial begin
     r_pll_clk         = 1'b0;