fpga: remove the API for configuring the UART core

This removes the possibility to configure the bit rate, data bits and stop bits at runtime from the API. This reduces the usage of LCs with ~4%. It is still possible to configure the core before building.
tillitis · Nov 19, 2024 · 24605df · 24605df
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Showing 3 changed files with 15 additions and 90 deletions.
diff --git a/hw/application_fpga/core/uart/README.md b/hw/application_fpga/core/uart/README.md
@@ -15,26 +15,24 @@ have to wait for bytes and poll them as soon as they are received. The
 number of bytes in the FIFO is also exposed to the SW through the
 ADDR_RX_BYTES address.
 
-The number of data and data bits can be set by SW. The default is
-eight data bits and one stop bit.
+The number of data and stop bits can be configured prior to building
+the core.
 
-The default bit rate is based on target clock frequency divided by the
-bit rate times in order to hit the center of the bits. I.e.  Clock: 18
-MHz, 62500 bps Divisor = 18E6 / 62500 = 288
+The bit rate can also be configured prior to building the core. It
+should be based on the target clock frequency divided by the bit rate
+in order to hit the center of the bits. For example, a clock of 18 MHz
+and a target bit rate of 62500 bps yields:
+Divisor = 18E6 / 62500 = 288
 
 ## API
 
 ```
-  ADDR_BIT_RATE:  0x10
-  ADDR_DATA_BITS: 0x11
-  ADDR_STOP_BITS: 0x12
+ADDR_RX_STATUS: 0x20
+ADDR_RX_DATA:   0x21
+ADDR_RX_BYTES:  0x22
 
-  ADDR_RX_STATUS: 0x20
-  ADDR_RX_DATA:   0x21
-  ADDR_RX_BYTES:  0x22
-
-  ADDR_TX_STATUS: 0x40
-  ADDR_TX_DATA:   0x41
+ADDR_TX_STATUS: 0x40
+ADDR_TX_DATA:   0x41
 ```
 
 ## Implementation notes.

diff --git a/hw/application_fpga/core/uart/rtl/uart.v b/hw/application_fpga/core/uart/rtl/uart.v
@@ -69,10 +69,6 @@ module uart (
   //----------------------------------------------------------------
   // Internal constant and parameter definitions.
   //----------------------------------------------------------------
-  localparam ADDR_BIT_RATE = 8'h10;
-  localparam ADDR_DATA_BITS = 8'h11;
-  localparam ADDR_STOP_BITS = 8'h12;
-
   localparam ADDR_RX_STATUS = 8'h20;
   localparam ADDR_RX_DATA = 8'h21;
   localparam ADDR_RX_BYTES = 8'h22;
@@ -94,15 +90,6 @@ module uart (
   //----------------------------------------------------------------
   // Registers including update variables and write enable.
   //----------------------------------------------------------------
-  reg  [15 : 0] bit_rate_reg;
-  reg           bit_rate_we;
-
-  reg  [ 3 : 0] data_bits_reg;
-  reg           data_bits_we;
-
-  reg  [ 1 : 0] stop_bits_reg;
-  reg           stop_bits_we;
-
 
   //----------------------------------------------------------------
   // Wires.
@@ -139,9 +126,9 @@ module uart (
       .reset_n(reset_n),
 
       // Configuration parameters
-      .bit_rate (bit_rate_reg),
-      .data_bits(data_bits_reg),
-      .stop_bits(stop_bits_reg),
+      .bit_rate (DEFAULT_BIT_RATE),
+      .data_bits(DEFAULT_DATA_BITS),
+      .stop_bits(DEFAULT_STOP_BITS),
 
       // External data interface
       .rxd(rxd),
@@ -174,36 +161,6 @@ module uart (
       .out_ack (fifo_out_ack)
   );
 
-
-  //----------------------------------------------------------------
-  // reg_update
-  //
-  // Update functionality for all registers in the core.
-  // All registers are positive edge triggered with synchronous
-  // active low reset.
-  //----------------------------------------------------------------
-  always @(posedge clk) begin : reg_update
-    if (!reset_n) begin
-      bit_rate_reg  <= DEFAULT_BIT_RATE;
-      data_bits_reg <= DEFAULT_DATA_BITS;
-      stop_bits_reg <= DEFAULT_STOP_BITS;
-    end
-    else begin
-      if (bit_rate_we) begin
-        bit_rate_reg <= write_data[15 : 0];
-      end
-
-      if (data_bits_we) begin
-        data_bits_reg <= write_data[3 : 0];
-      end
-
-      if (stop_bits_we) begin
-        stop_bits_reg <= write_data[1 : 0];
-      end
-    end
-  end  // reg_update
-
-
   //----------------------------------------------------------------
   // api
   //
@@ -212,9 +169,6 @@ module uart (
   //----------------------------------------------------------------
   always @* begin : api
     // Default assignments.
-    bit_rate_we   = 1'h0;
-    data_bits_we  = 1'h0;
-    stop_bits_we  = 1'h0;
     core_txd_syn  = 1'h0;
     fifo_out_ack  = 1'h0;
     tmp_read_data = 32'h0;
@@ -227,18 +181,6 @@ module uart (
 
       if (we) begin
         case (address)
-          ADDR_BIT_RATE: begin
-            bit_rate_we = 1;
-          end
-
-          ADDR_DATA_BITS: begin
-            data_bits_we = 1;
-          end
-
-          ADDR_STOP_BITS: begin
-            stop_bits_we = 1;
-          end
-
           ADDR_TX_DATA: begin
             if (core_txd_ready) begin
               core_txd_syn = 1'h1;
@@ -252,18 +194,6 @@ module uart (
 
       else begin
         case (address)
-          ADDR_BIT_RATE: begin
-            tmp_read_data = {16'h0, bit_rate_reg};
-          end
-
-          ADDR_DATA_BITS: begin
-            tmp_read_data = {28'h0, data_bits_reg};
-          end
-
-          ADDR_STOP_BITS: begin
-            tmp_read_data = {30'h0, stop_bits_reg};
-          end
-
           ADDR_RX_STATUS: begin
             tmp_read_data = {31'h0, fifo_out_syn};
           end

diff --git a/hw/application_fpga/fw/tk1_mem.h b/hw/application_fpga/fw/tk1_mem.h
@@ -86,9 +86,6 @@
 #define TK1_MMIO_UDS_LAST 0xc200005c
 
 #define TK1_MMIO_UART_BASE 0xc3000000
-#define TK1_MMIO_UART_BIT_RATE 0xc3000040
-#define TK1_MMIO_UART_DATA_BITS 0xc3000044
-#define TK1_MMIO_UART_STOP_BITS 0xc3000048
 #define TK1_MMIO_UART_RX_STATUS 0xc3000080
 #define TK1_MMIO_UART_RX_DATA 0xc3000084
 #define TK1_MMIO_UART_RX_BYTES 0xc3000088