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Fixed mask assignment error, made usage, variables more clear

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Kip Macsai-Goren 2021-06-22 13:31:06 -04:00
parent 2c41da0275
commit 7e06a3c04d
1 changed files with 12 additions and 11 deletions
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23
wally-pipelined/src/mmu/physicalpagemask.sv
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@ -7,6 +7,7 @@
//
// Purpose: Takes two page numbers and replaces segments of the first page
// number with segments from the second, based on the page type.
// NOTE: this DOES NOT include the 12 bit offset, which is the same no matter the translation mode or page type.
//
// A component of the Wally configurable RISC-V project.
//
@ -36,26 +37,26 @@ module physicalpagemask (
);
localparam EXTRA_BITS = `PPN_BITS - `VPN_BITS;
logic [`PPN_BITS-1:0] ZeroExtendedVPN = {{EXTRA_BITS{1'b0}}, VPN}; // forces the VPN to be the same width as PPN.
logic [`PPN_BITS-1:0] OffsetMask;
logic [`PPN_BITS-1:0] ZeroExtendedVPN;
logic [`PPN_BITS-1:0] PageNumberMask;
assign ZeroExtendedVPN = {{EXTRA_BITS{1'b0}}, VPN}; // forces the VPN to be the same width as PPN.
generate
if (`XLEN == 32) begin
always_comb
case (PageType[0])
// *** the widths of these constansts are hardocded here to match `PPN_BITS in the wally-constants file.
0: OffsetMask = 22'h3FFFFF; // kilopage: 22 bits of PPN, 0 bits of VPN
1: OffsetMask = 22'h3FFC00; // megapage: 12 bits of PPN, 10 bits of VPN
0: PageNumberMask = 22'h3FFFFF; // kilopage: 22 bits of PPN, 0 bits of VPN
1: PageNumberMask = 22'h3FFC00; // megapage: 12 bits of PPN, 10 bits of VPN
endcase
end else begin
always_comb
case (PageType[1:0])
0: OffsetMask = 44'hFFFFFFFFFFF; // kilopage: 44 bits of PPN, 0 bits of VPN
1: OffsetMask = 44'hFFFFFFFFE00; // megapage: 35 bits of PPN, 9 bits of VPN
2: OffsetMask = 44'hFFFFFFC0000; // gigapage: 26 bits of PPN, 18 bits of VPN
3: OffsetMask = 44'hFFFF8000000; // terapage: 17 bits of PPN, 27 bits of VPN
0: PageNumberMask = 44'hFFFFFFFFFFF; // kilopage: 44 bits of PPN, 0 bits of VPN
1: PageNumberMask = 44'hFFFFFFFFE00; // megapage: 35 bits of PPN, 9 bits of VPN
2: PageNumberMask = 44'hFFFFFFC0000; // gigapage: 26 bits of PPN, 18 bits of VPN
3: PageNumberMask = 44'hFFFF8000000; // terapage: 17 bits of PPN, 27 bits of VPN
// *** make sure that this doesnt break when using sv39. In that case, all of these
// busses are the widths for sv48, but extra bits should be zeroed out by the mux
// in the tlb when it generates VPN from the full virtualadress.
@ -63,7 +64,7 @@ module physicalpagemask (
end
endgenerate
// merge low bits of the virtual address containing the offset with high bits of the PPN
assign MixedPageNumber = (ZeroExtendedVPN & ~OffsetMask) | (PPN & OffsetMask);
// merge low segments of VPN with high segments of PPN decided by the pagetype.
assign MixedPageNumber = (ZeroExtendedVPN & ~PageNumberMask) | (PPN & PageNumberMask);
endmodule