[i2c,rtl] Count number of NACKs sent

This is useful for software to know how many NACKs have happened since
the ACQ FIFO ended up being full. Otherwise there is no way for software
to know whether it was on time with emptying the FIFO or whether it just
missed the one byte or whether it missed multiple transactions.

Signed-off-by: Marno van der Maas <[email protected]>

hw/ip/i2c/rtl/i2c_core.sv

@@ -76,6 +76,7 @@ module i2c_core import i2c_pkg::*;
   logic event_stretch_timeout;
   logic event_sda_unstable;
   logic event_cmd_complete;
+  logic event_target_nack;
   logic event_tx_stretch;
   logic event_unexp_stop;
   logic event_host_timeout;
@@ -187,6 +188,9 @@ module i2c_core import i2c_pkg::*;
   assign hw2reg.target_fifo_status.acqlvl.d = MaxFifoDepthW'(acq_fifo_depth);
   assign hw2reg.acqdata.abyte.d = acq_fifo_rdata[7:0];
   assign hw2reg.acqdata.signal.d = acq_fifo_rdata[AcqFifoWidth-1:8];
+  // Add one to the target NACK count if this target has sent a NACK.
+  assign hw2reg.target_nack_count.de = event_target_nack;
+  assign hw2reg.target_nack_count.d = reg2hw.target_nack_count.q + 1;
 
   assign override = reg2hw.ovrd.txovrden;
 
@@ -469,6 +473,7 @@ module i2c_core import i2c_pkg::*;
     .target_mask0_i          (target_mask0),
     .target_address1_i       (target_address1),
     .target_mask1_i          (target_mask1),
+    .event_target_nack_o     (event_target_nack),
     .event_nak_o             (event_nak),
     .event_scl_interference_o(event_scl_interference),
     .event_sda_interference_o(event_sda_interference),

hw/ip/i2c/rtl/i2c_fsm.sv

@@ -73,6 +73,7 @@ module i2c_fsm import i2c_pkg::*;
   input logic [6:0] target_address1_i,
   input logic [6:0] target_mask1_i,
 
+  output logic event_target_nack_o,      // this target sent a NACK (this is used to keep count)
   output logic event_nak_o,              // target didn't Ack when expected
   output logic event_scl_interference_o, // other device forcing SCL low
   output logic event_sda_interference_o, // other device forcing SDA low
@@ -518,6 +519,7 @@ module i2c_fsm import i2c_pkg::*;
     event_scl_interference_o = 1'b0;
     event_sda_unstable_o = 1'b0;
     event_cmd_complete_o = 1'b0;
+    event_target_nack_o = 1'b0;
     rw_bit = rw_bit_q;
     stretch_en = 1'b0;
     expect_stop = 1'b0;
@@ -832,6 +834,7 @@ module i2c_fsm import i2c_pkg::*;
           // complete notification from a restart or a stop. We must notify
           // software that it needs to start processing the ACQ FIFO.
           event_cmd_complete_o = 1'b1;
+          event_target_nack_o = 1'b1;
         end
       end
       // StretchAddr: target stretches the clock if matching address cannot be
@@ -881,6 +884,7 @@ module i2c_fsm import i2c_pkg::*;
         event_scl_interference_o = 1'b0;
         event_sda_unstable_o = 1'b0;
         event_cmd_complete_o = 1'b0;
+        event_target_nack_o = 1'b0;
         actively_stretching = 1'b0;
       end
     endcase // unique case (state_q)