untethered rocket-chip simulation?
by Gabriel L. Somlo
I'm trying to run the rocketchip through a simulator, but without
the (imho massive) tethering infrastructure that usually surrounds
it (gdb/fesvr/dtm/jtag), just to see how its bits and pieces wobble,
and to maybe see it tickle its AXI interface(s) to memory and MMIO.
So I grabbed the current rocket sources and built one of the
configurations (shouldn't much matter which one, but in my
case I picked DefaultFPGASmallConfig):
git clone --recursive \
https://github.com/freechipsproject/rocket-chip.git
make RISCV=${HOME}/RISCV -C rocket-chip/vsim \
verilog CONFIG=DefaultFPGASmallConfig
I wrote the smallest testbench wrapper I could think of, and also
replaced SimDTM (the default tether) with a stub returning 0s for
everything:
// begin FILE: tb.v
module testbench();
// clock & reset:
reg clk = 1'b1;
always #5 clk = ~clk;
reg rst = 1'b1;
initial #103 rst = 1'b0;
// DUT declaration:
wire result;
TestHarness dut (
.clock(clk),
.reset(rst),
.io_success(result)
);
// DUT simulation:
initial begin
$dumpfile("testbench.vcd");
$dumpvars(0, testbench);
$monitor($time, " ########################################\n",
"\t\tresult=%b\n", result,
"\t\tpc=%h\n", dut.dut.tile.core.ex_reg_pc,
);
repeat (3) begin
repeat (10) @(posedge clk);
$display("+10 cycles");
end
$finish;
end
endmodule // testbench
// stub "tether" to satisfy dependencies:
module SimDTM(
input clk,
input reset,
output debug_req_valid,
input debug_req_ready,
output [ 6:0] debug_req_bits_addr,
output [ 1:0] debug_req_bits_op,
output [31:0] debug_req_bits_data,
input debug_resp_valid,
output debug_resp_ready,
input [ 1:0] debug_resp_bits_resp,
input [31:0] debug_resp_bits_data,
output [31:0] exit
);
assign debug_req_valid = 1'b0;
assign debug_resp_ready = 1'b0;
assign exit = 32'h0;
assign debug_req_bits_addr = 7'h0;
assign debug_req_bits_op = 2'h0;
assign debug_req_bits_data = 32'h0;
endmodule // SimDTM
// end FILE: tb.v
I tried building this with both iverilog and VCS, so either:
iverilog -s testbench -o tb.vvp tb.v \
rocket-chip/src/main/resources/vsrc/AsyncResetReg.v \
rocket-chip/src/main/resources/vsrc/EICG_wrapper.v \
rocket-chip/src/main/resources/vsrc/plusarg_reader.v \
rocket-chip/vsim/generated-src/freechips.rocketchip.system.DefaultFPGASmallConfig.v \
rocket-chip/vsim/generated-src/freechips.rocketchip.system.DefaultFPGASmallConfig.behav_srams.v
or:
vcs -q -nc -sverilog -top testbench -o tb.simv tb.v \
rocket-chip/src/main/resources/vsrc/AsyncResetReg.v \
rocket-chip/src/main/resources/vsrc/EICG_wrapper.v \
rocket-chip/src/main/resources/vsrc/plusarg_reader.v \
rocket-chip/vsim/generated-src/freechips.rocketchip.system.DefaultFPGASmallConfig.v \
rocket-chip/vsim/generated-src/freechips.rocketchip.system.DefaultFPGASmallConfig.behav_srams.v
When I run the simulation (either via 'vvp -N tb.vvp' or the
VCS-produced './tb.simv'), I would expect the core to spin around
the "hang" loop at 0x10040 (as per the included bootrom), or to
start knocking about the "main memory" in behav_srams.v if I changed
the reset vector to 0x8000_0000. Instead, the simulated rocket-chip
is stuck in an undefined state:
0 ########################################
result=0
pc=xxxxxxxxx
+10 cycles
C 0: 0 [0] pc=[0000000Xxxxxxxxx] W[r 0=xxxxxxxxxxxxxxxx][0] R[r x=xxxxxxxxxxxxxxxx] R[r x=xxxxxxxxxxxxxxxx] inst=[xxxxxxxx] DASM(xxxxxxxx)
C 0: 1 [0] pc=[0000000Xxxxxxxxx] W[r 0=xxxxxxxxxxxxxxxx][0] R[r x=xxxxxxxxxxxxxxxx] R[r x=xxxxxxxxxxxxxxxx] inst=[xxxxxxxx] DASM(xxxxxxxx)
C 0: 2 [0] pc=[0000000Xxxxxxxxx] W[r 0=xxxxxxxxxxxxxxxx][0] R[r x=xxxxxxxxxxxxxxxx] R[r x=xxxxxxxxxxxxxxxx] inst=[xxxxxxxx] DASM(xxxxxxxx)
C 0: 3 [0] pc=[0000000Xxxxxxxxx] W[r 0=xxxxxxxxxxxxxxxx][0] R[r x=xxxxxxxxxxxxxxxx] R[r x=xxxxxxxxxxxxxxxx] inst=[xxxxxxxx] DASM(xxxxxxxx)
C 0: 4 [x] pc=[0000000Xxxxxxxxx] W[r x=xxxxxxxxxxxxxxxx][x] R[r x=xxxxxxxxxxxxxxxx] R[r x=xxxxxxxxxxxxxxxx] inst=[xxxxxxxx] DASM(xxxxxxxx)
C 0: X [x] pc=[0000000Xxxxxxxxx] W[r x=xxxxxxxxxxxxxxxx][x] R[r x=xxxxxxxxxxxxxxxx] R[r x=xxxxxxxxxxxxxxxx] inst=[xxxxxxxx] DASM(xxxxxxxx)
C 0: X [x] pc=[0000000Xxxxxxxxx] W[r x=xxxxxxxxxxxxxxxx][x] R[r x=xxxxxxxxxxxxxxxx] R[r x=xxxxxxxxxxxxxxxx] inst=[xxxxxxxx] DASM(xxxxxxxx)
C 0: X [x] pc=[0000000Xxxxxxxxx] W[r x=xxxxxxxxxxxxxxxx][x] R[r x=xxxxxxxxxxxxxxxx] R[r x=xxxxxxxxxxxxxxxx] inst=[xxxxxxxx] DASM(xxxxxxxx)
...
I'm sure I must be missing something (after all the rocket-chip
works just fine when hooked into the rest of lowRISC :).
I'm wondering if anyone on this list ever encountered something
similar, and what the missing piece of the puzzle might have been.
Thanks in advance for any clues,
--Gabriel
4 years, 8 months
