[otbn] Don't wrap link register values to size of dmem
If we execute a JAL or JALR from address 0xffc (the top word in
memory), we want to store a link address of 0x1000 rather than zero.
Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>
diff --git a/hw/ip/otbn/rtl/otbn_controller.sv b/hw/ip/otbn/rtl/otbn_controller.sv
index 40a5f55..24725bc 100644
--- a/hw/ip/otbn/rtl/otbn_controller.sv
+++ b/hw/ip/otbn/rtl/otbn_controller.sv
@@ -119,8 +119,8 @@
logic branch_taken;
logic [ImemAddrWidth-1:0] branch_target;
logic branch_target_overflow;
+ logic [ImemAddrWidth:0] next_insn_addr_wide;
logic [ImemAddrWidth-1:0] next_insn_addr;
- logic next_insn_addr_overflow;
csr_e csr_addr;
logic [31:0] csr_rdata_raw;
@@ -189,7 +189,8 @@
assign branch_target = alu_base_operation_result_i[ImemAddrWidth-1:0];
assign branch_target_overflow = |alu_base_operation_result_i[31:ImemAddrWidth];
- assign {next_insn_addr_overflow, next_insn_addr} = insn_addr_i + 'd4;
+ assign next_insn_addr_wide = {1'b0, insn_addr_i} + 'd4;
+ assign next_insn_addr = next_insn_addr_wide[ImemAddrWidth-1:0];
always_comb begin
// `state_raw` and `insn_fetch_req_valid_raw` are the values of `state_d` and
@@ -256,7 +257,7 @@
end else if (branch_taken) begin
imem_addr_err = branch_target_overflow;
end else begin
- imem_addr_err = next_insn_addr_overflow;
+ imem_addr_err = next_insn_addr_wide[ImemAddrWidth];
end
end
end
@@ -421,7 +422,7 @@
unique case (insn_dec_base_i.rf_wdata_sel)
RfWdSelEx: rf_base_wr_data_o = alu_base_operation_result_i;
RfWdSelLsu: rf_base_wr_data_o = lsu_base_rdata_i;
- RfWdSelNextPc: rf_base_wr_data_o = {{(32-ImemAddrWidth){1'b0}}, next_insn_addr};
+ RfWdSelNextPc: rf_base_wr_data_o = {{(32-(ImemAddrWidth+1)){1'b0}}, next_insn_addr_wide};
RfWdSelIspr: rf_base_wr_data_o = csr_rdata;
RfWdSelIncr: rf_base_wr_data_o = increment_out;
default: rf_base_wr_data_o = alu_base_operation_result_i;
