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Make the offset in the BTB variable

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This commit is contained in:
Florian Zaruba 2017-04-19 20:52:23 +02:00
parent 8e26881686
commit f7f303988e
2 changed files with 11 additions and 2 deletions
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7
btb.sv
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@ -34,6 +34,9 @@ module btb #(
output logic predict_taken_o, // the branch is taken
output logic [63:0] branch_target_address_o // instruction has the following target address
);
// number of bits which are not used for indexing
localparam OFFSET = 2;
// typedef for all branch target entries
// we may want to try to put a tag field that fills the rest of the PC in-order to mitigate aliasing effects
struct packed {
@ -48,8 +51,8 @@ module btb #(
// get actual index positions
// we ignore the 0th bit since all instructions are aligned on
// a half word boundary
assign update_pc = misspredict_i.pc[$clog2(NR_ENTRIES):1];
assign index = vpc_i[$clog2(NR_ENTRIES):1];
assign update_pc = misspredict_i.pc[$clog2(NR_ENTRIES) + OFFSET - 1:OFFSET];
assign index = vpc_i[$clog2(NR_ENTRIES) + OFFSET - 1:OFFSET];
// we combinatorially predict the branch and the target address
assign is_branch_o = btb_q[$unsigned(index)].valid;

6
include/ariane_pkg.svh
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@ -106,6 +106,11 @@ package ariane_pkg;
logic [6:0] opcode;
} utype;
// for some reason verilator complains about this union
// since I am not using it for simulation anyway and linting only
// it is not too bad to deactivate it, but a future me (or you)
// should look into that more thoroughly
`ifndef verilator
typedef union packed {
logic [31:0] instr;
rtype rtype;
@ -113,6 +118,7 @@ package ariane_pkg;
stype stype;
utype utype;
} instruction;
`endif
// --------------------
// Opcodes