src/lib/axi_addr_generator.bsv

   1 package axi_addr_generator;
   2         /*=== Project imports ===*/
   3         import defined_types::*;
   4         `include "instance_defines.bsv"
   5         /*=======================*/
   6
   7         // This function is used by the slaves on the AXI4 bus to generate the sequential addresses in burst mode.
   8         // the different modes supported are :
   9         // FIXED: the same address is sent in all transactions. Typically used in polling modes.
  10         // INCR: The address is simply incremented arlen number of times from the starting address.
  11         // WRAP: This mode supports only 4 valid lengths: 2, 4 8 and 16 bursts. the increments happen in a wrap arouind fashion.
  12         function Bit#(`PADDR) burst_address_generator(Bit#(8) arlen, Bit#(3) arsize, Bit#(2) arburst, Bit#(`PADDR) address);
  13
  14                 // this variable will decide the index above which part of the address should
  15                 // not change in WRAP mode. Bits below this index value be incremented according
  16                 // to the value of arlen and arsize;
  17                 Bit#(3) wrap_size;
  18                 case(arlen)
  19                         3: wrap_size= 2;
  20                         7: wrap_size= 3;
  21                         15: wrap_size=4;
  22                         default:wrap_size=1;
  23                 endcase
  24
  25                 Bit#(`PADDR) new_address=address+(('b1)<<arsize); // this is address will directly be used for INCR mode.
  26                 Bit#(`PADDR) mask;
  27                 mask=('1)<<(arsize+wrap_size);                                            // create a mask for bits which will remain constant in wrap mode.
  28                 Bit#(`PADDR) temp1=address& mask;                                         // capture the constant part of the address in WRAP mode.
  29                 Bit#(`PADDR) temp2=new_address& (~mask);                          // capture the incremental part of the address in WRAP mode.
  30
  31                 if(arburst==0) // FIXED
  32                         return address;
  33                 else if(arburst==1)begin // INCR
  34                         return new_address;
  35                 end
  36                 else begin // WRAP
  37                         return temp1|temp2;                                                                       // create the new address in the wrap mode by ORing the masked values.
  38                 end
  39         endfunction
  40 endpackage