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[bus] Return error if decode fails

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Return an error signal to the host if an address request
does not match any device.
Previously a decode failure would match against the first
device, which in the Ibex Demo System happens to be
the SRAM.
This commit is contained in:
Adrian Lees 2024-02-15 14:56:04 +00:00 • committed by alees24
parent 14c2b3f7ab
commit ea1a208f8d
1 changed files with 14 additions and 3 deletions
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17
shared/rtl/bus.sv
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@ -54,14 +54,20 @@ module bus #(
localparam int unsigned NumBitsHostSel = NrHosts > 1 ? $clog2(NrHosts) : 1;
localparam int unsigned NumBitsDeviceSel = NrDevices > 1 ? $clog2(NrDevices) : 1;
logic host_sel_valid;
logic device_sel_valid;
logic decode_err_resp;
logic [NumBitsHostSel-1:0] host_sel_req, host_sel_resp;
logic [NumBitsDeviceSel-1:0] device_sel_req, device_sel_resp;
// Master select prio arbiter
always_comb begin
host_sel_valid = 1'b0;
host_sel_req = '0;
for (integer host = NrHosts - 1; host >= 0; host = host - 1) begin
if (host_req_i[host]) begin
host_sel_valid = 1'b1;
host_sel_req = NumBitsHostSel'(host);
end
end
@ -69,10 +75,12 @@ module bus #(
// Device select
always_comb begin
device_sel_valid = 1'b0;
device_sel_req = '0;
for (integer device = 0; device < NrDevices; device = device + 1) begin
if ((host_addr_i[host_sel_req] & cfg_device_addr_mask[device])
== cfg_device_addr_base[device]) begin
device_sel_valid = 1'b1;
device_sel_req = NumBitsDeviceSel'(device);
end
end
@ -82,16 +90,19 @@ module bus #(
if (!rst_ni) begin
host_sel_resp <= '0;
device_sel_resp <= '0;
decode_err_resp <= 1'b0;
end else begin
// Responses are always expected 1 cycle after the request
device_sel_resp <= device_sel_req;
host_sel_resp <= host_sel_req;
// Decode failed; no device matched?
decode_err_resp <= host_sel_valid & !device_sel_valid;
end
end
always_comb begin
for (integer device = 0; device < NrDevices; device = device + 1) begin
if (NumBitsDeviceSel'(device) == device_sel_req) begin
if (device_sel_valid && NumBitsDeviceSel'(device) == device_sel_req) begin
device_req_o[device] = host_req_i[host_sel_req];
device_we_o[device] = host_we_i[host_sel_req];
device_addr_o[device] = host_addr_i[host_sel_req];
@ -111,8 +122,8 @@ module bus #(
for (integer host = 0; host < NrHosts; host = host + 1) begin
host_gnt_o[host] = 1'b0;
if (NumBitsHostSel'(host) == host_sel_resp) begin
host_rvalid_o[host] = device_rvalid_i[device_sel_resp];
host_err_o[host] = device_err_i[device_sel_resp];
host_rvalid_o[host] = device_rvalid_i[device_sel_resp] | decode_err_resp;
host_err_o[host] = device_err_i[device_sel_resp] | decode_err_resp;
host_rdata_o[host] = device_rdata_i[device_sel_resp];
end else begin
host_rvalid_o[host] = 1'b0;