implement i2c ping

[guruofquality]

I wanted to be able to discover if a slave was available on the bus by using a ping. Basically a ping will only send the address, and then the stop condition. The missed_ack signal is used to determine the presence of the slave.

I made the following addition to i2c_master.v to add a s_axis_cmd_ping input signal that can cause STATE_ADDRESS_2 to transition to STATE_STOP, rather than read or write a byte.

I would like to upstream the change. Should I make a pull request? Is this a "fitting" way to add ping support to this module? Should the pull add support for ping in i2c_master_axil.v i2c_master_wbs_16.v i2c_master_wbs_8.v?

diff --git a/rtl/i2c_master.v b/rtl/i2c_master.v
index 9c69b48..caacdf2 100644
--- a/rtl/i2c_master.v
+++ b/rtl/i2c_master.v
@@ -38,6 +38,7 @@ module i2c_master (
      */
     input  wire [6:0]  s_axis_cmd_address,
     input  wire        s_axis_cmd_start,
+    input  wire        s_axis_cmd_ping,
     input  wire        s_axis_cmd_read,
     input  wire        s_axis_cmd_write,
     input  wire        s_axis_cmd_write_multiple,
@@ -232,6 +233,7 @@ reg [6:0] addr_reg = 7'd0, addr_next;
 reg [7:0] data_reg = 8'd0, data_next;
 reg last_reg = 1'b0, last_next;
 
+reg mode_ping_reg = 1'b0, mode_ping_next;
 reg mode_read_reg = 1'b0, mode_read_next;
 reg mode_write_multiple_reg = 1'b0, mode_write_multiple_next;
 reg mode_stop_reg = 1'b0, mode_stop_next;
@@ -304,6 +306,7 @@ always @* begin
     data_next = data_reg;
     last_next = last_reg;
 
+    mode_ping_next = mode_ping_reg;
     mode_read_next = mode_read_reg;
     mode_write_multiple_next = mode_write_multiple_reg;
     mode_stop_next = mode_stop_reg;
@@ -364,9 +367,10 @@ always @* begin
 
                 if (s_axis_cmd_ready & s_axis_cmd_valid) begin
                     // command valid
-                    if (s_axis_cmd_read ^ (s_axis_cmd_write | s_axis_cmd_write_multiple)) begin
+                    if (s_axis_cmd_ping ^ s_axis_cmd_read ^ (s_axis_cmd_write | s_axis_cmd_write_multiple)) begin
                         // read or write command
                         addr_next = s_axis_cmd_address;
+                        mode_ping_next = s_axis_cmd_ping;
                         mode_read_next = s_axis_cmd_read;
                         mode_write_multiple_next = s_axis_cmd_write_multiple;
                         mode_stop_next = s_axis_cmd_stop;
@@ -510,6 +514,8 @@ always @* begin
                     bit_count_next = 4'd8;
                     data_next = 1'b0;
                     state_next = STATE_READ;
+                end else if (mode_ping_reg) begin
+                    state_next = STATE_STOP;
                 end else begin
                     // start write
                     s_axis_data_tready_next = 1'b1;