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fpga: remove the API for configuring the UART core
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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.
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@dehanj
dehanj committed Nov 26, 2024
1 parent 0445c8f commit b151d6b
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Showing 4 changed files with 16 additions and 94 deletions.
5 changes: 1 addition & 4 deletions hw/application_fpga/README.md
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Expand Up @@ -184,10 +184,7 @@ HKDF.
A simple universal asynchronous receiver/transmitter (UART) used for
communication with the client through the USB controller.

The UART default speed is 62500 bps, but can be adjusted by the
application. (Note that the host must set the same bitrate too.)

The UART contain a 512 but Rx-FIFO with status (data available).
The UART contain a 512-byte Rx-FIFO with status (data available).

The UART is available to use by firmware and applications.

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26 changes: 12 additions & 14 deletions hw/application_fpga/core/uart/README.md
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Expand Up @@ -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.
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76 changes: 3 additions & 73 deletions hw/application_fpga/core/uart/rtl/uart.v
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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.
Expand Down Expand Up @@ -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),
Expand Down Expand Up @@ -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
//
Expand All @@ -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;
Expand All @@ -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;
Expand All @@ -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
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3 changes: 0 additions & 3 deletions hw/application_fpga/fw/tk1_mem.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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
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