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Issue openhwgroup#170 correction:
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Added MSTATUS.FS and SD and all their control.
Added fs_off_o for instructions decoder to generate illegal instructions when FS is OFF.

Signed-off-by: Pascal Gouedo <[email protected]>
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Pascal Gouedo committed Apr 19, 2023
1 parent 504c2a2 commit 6c1855c
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Showing 4 changed files with 118 additions and 60 deletions.
5 changes: 4 additions & 1 deletion rtl/cv32e40p_core.sv
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Original file line number Diff line number Diff line change
Expand Up @@ -197,6 +197,7 @@ module cv32e40p_core
logic mult_clpx_img_ex;

// FPU
logic fs_off;
logic [ C_RM-1:0] frm_csr;
logic [ C_FFLAG-1:0] fflags_csr;
logic fflags_we;
Expand Down Expand Up @@ -608,7 +609,8 @@ module cv32e40p_core
.mult_clpx_img_ex_o (mult_clpx_img_ex), // from ID to EX stage

// FPU
.frm_i(frm_csr),
.fs_off_i(fs_off),
.frm_i (frm_csr),

// APU
.apu_en_ex_o (apu_en_ex),
Expand Down Expand Up @@ -953,6 +955,7 @@ module cv32e40p_core
.csr_op_i (csr_op),
.csr_rdata_o (csr_rdata),

.fs_off_o (fs_off),
.frm_o (frm_csr),
.fflags_i (fflags_csr),
.fflags_we_i(fflags_we),
Expand Down
89 changes: 70 additions & 19 deletions rtl/cv32e40p_cs_registers.sv
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,7 @@ module cv32e40p_cs_registers
input csr_opcode_e csr_op_i,
output logic [31:0] csr_rdata_o,

output logic fs_off_o,
output logic [ 2:0] frm_o,
input logic [C_FFLAG-1:0] fflags_i,
input logic fflags_we_i,
Expand Down Expand Up @@ -151,9 +152,12 @@ module cv32e40p_cs_registers
localparam MSTATUS_SPIE_BIT = 5;
localparam MSTATUS_MPIE_BIT = 7;
localparam MSTATUS_SPP_BIT = 8;
localparam MSTATUS_MPP_BIT_HIGH = 12;
localparam MSTATUS_MPP_BIT_LOW = 11;
localparam MSTATUS_MPP_BIT_HIGH = 12;
localparam MSTATUS_FS_BIT_LOW = 13;
localparam MSTATUS_FS_BIT_HIGH = 14;
localparam MSTATUS_MPRV_BIT = 17;
localparam MSTATUS_SD_BIT = 31;

// misa
localparam logic [1:0] MXL = 2'd1; // M-XLEN: XLEN in M-Mode for RV32
Expand All @@ -175,6 +179,14 @@ module cv32e40p_cs_registers
// but only HPMCOUNTERs (depending on NUM_MHPMCOUNTERS)
localparam PULP_PERF_COUNTERS = 0;

// Floating Point State
typedef enum logic [1:0] {
FS_OFF = 2'b00,
FS_INITIAL = 2'b01,
FS_CLEAN = 2'b10,
FS_DIRTY = 2'b11
} FS_t;

typedef struct packed {
logic uie;
// logic sie; - unimplemented, hardwired to '0
Expand Down Expand Up @@ -218,8 +230,11 @@ module cv32e40p_cs_registers
logic [31:0] csr_wdata_int;
logic [31:0] csr_rdata_int;
logic csr_we_int;

// FPU
logic [C_RM-1:0] frm_q, frm_n;
logic [C_FFLAG-1:0] fflags_q, fflags_n;
logic fcsr_update;

// Interrupt control signals
logic [31:0] mepc_q, mepc_n;
Expand All @@ -237,6 +252,7 @@ module cv32e40p_cs_registers

logic [31:0] exception_pc;
Status_t mstatus_q, mstatus_n;
FS_t mstatus_fs_q, mstatus_fs_n;
logic [5:0] mcause_q, mcause_n;
logic [5:0] ucause_q, ucause_n;
//not implemented yet
Expand Down Expand Up @@ -488,9 +504,11 @@ module cv32e40p_cs_registers
// mstatus: always M-mode, contains IE bit
CSR_MSTATUS:
csr_rdata_int = {
14'b0,
(FPU == 1) ? (mstatus_fs_q == FS_DIRTY ? 1'b1 : 1'b0) : 1'b0,
13'b0,
mstatus_q.mprv,
4'b0,
2'b0,
(FPU == 1) ? mstatus_fs_q : FS_OFF,
mstatus_q.mpp,
3'b0,
mstatus_q.mpie,
Expand Down Expand Up @@ -897,8 +915,12 @@ module cv32e40p_cs_registers
end else begin : gen_no_pulp_secure_write_logic //PULP_SECURE == 0
// write logic
always_comb begin
fflags_n = fflags_q;
frm_n = frm_q;
if (FPU == 1) begin
fflags_n = fflags_q;
frm_n = frm_q;
mstatus_fs_n = mstatus_fs_q;
fcsr_update = 1'b0;
end
mscratch_n = mscratch_q;
mepc_n = mepc_q;
uepc_n = 'b0; // Not used if PULP_SECURE == 0
Expand All @@ -924,19 +946,32 @@ module cv32e40p_cs_registers
mtvec_mode_n = mtvec_mode_q;
utvec_mode_n = '0; // Not used if PULP_SECURE == 0

if (FPU == 1) if (fflags_we_i) fflags_n = fflags_i | fflags_q;

case (csr_addr_i)
// fcsr: Floating-Point Control and Status Register (frm, fflags, fprec).
CSR_FFLAGS: if (csr_we_int) fflags_n = (FPU == 1) ? csr_wdata_int[C_FFLAG-1:0] : '0;
CSR_FRM: if (csr_we_int) frm_n = (FPU == 1) ? csr_wdata_int[C_RM-1:0] : '0;
CSR_FFLAGS:
if (FPU == 1) begin
if (csr_we_int) begin
fcsr_update = 1'b1;
fflags_n = csr_wdata_int[C_FFLAG-1:0];
end
end
CSR_FRM:
if (FPU == 1) begin
if (csr_we_int) begin
fcsr_update = 1'b1;
frm_n = csr_wdata_int[C_RM-1:0];
end
end
CSR_FCSR:
if (csr_we_int) begin
fflags_n = (FPU == 1) ? csr_wdata_int[C_FFLAG-1:0] : '0;
frm_n = (FPU == 1) ? csr_wdata_int[C_RM+C_FFLAG-1:C_FFLAG] : '0;
if (FPU == 1) begin
if (csr_we_int) begin
fcsr_update = 1'b1;
fflags_n = csr_wdata_int[C_FFLAG-1:0];
frm_n = csr_wdata_int[C_RM+C_FFLAG-1:C_FFLAG];
end
end

// mstatus: IE bit
// mstatus
CSR_MSTATUS:
if (csr_we_int) begin
mstatus_n = '{
Expand All @@ -947,6 +982,9 @@ module cv32e40p_cs_registers
mpp: PrivLvl_t'(csr_wdata_int[MSTATUS_MPP_BIT_HIGH:MSTATUS_MPP_BIT_LOW]),
mprv: csr_wdata_int[MSTATUS_MPRV_BIT]
};
if (FPU) begin
mstatus_fs_n = FS_t'(csr_wdata_int[MSTATUS_FS_BIT_HIGH:MSTATUS_FS_BIT_LOW]);
end
end
// mie: machine interrupt enable
CSR_MIE:
Expand Down Expand Up @@ -1008,6 +1046,16 @@ module cv32e40p_cs_registers

endcase

if (FPU == 1) begin
if (fflags_we_i) begin
fflags_n = fflags_i | fflags_q;
end

if (fflags_we_i || fcsr_update) begin // FPU Register File/Flags implicit update or modified by CSR instructions
mstatus_fs_n = FS_DIRTY;
end
end

// exception controller gets priority over other writes
unique case (1'b1)

Expand Down Expand Up @@ -1078,6 +1126,9 @@ module cv32e40p_cs_registers
assign u_irq_enable_o = mstatus_q.uie && !(dcsr_q.step && !dcsr_q.stepie);
assign priv_lvl_o = priv_lvl_q;
assign sec_lvl_o = priv_lvl_q[0];

// mstatus_fs_q = FS_OFF, FPU not enabled
assign fs_off_o = (FPU == 1) ? (mstatus_fs_q == FS_OFF ? 1'b1 : 1'b0) : 1'b0;
assign frm_o = (FPU == 1) ? frm_q : '0;

assign mtvec_o = mtvec_q;
Expand Down Expand Up @@ -1147,8 +1198,11 @@ module cv32e40p_cs_registers
// actual registers
always_ff @(posedge clk, negedge rst_n) begin
if (rst_n == 1'b0) begin
frm_q <= '0;
fflags_q <= '0;
if (FPU == 1) begin
frm_q <= '0;
fflags_q <= '0;
mstatus_fs_q <= FS_OFF;
end
mstatus_q <= '{
uie: 1'b0,
mie: 1'b0,
Expand Down Expand Up @@ -1178,9 +1232,7 @@ module cv32e40p_cs_registers
if (FPU == 1) begin
frm_q <= frm_n;
fflags_q <= fflags_n;
end else begin
frm_q <= 'b0;
fflags_q <= 'b0;
mstatus_fs_q <= mstatus_fs_n;
end
if (PULP_SECURE == 1) begin
mstatus_q <= mstatus_n;
Expand Down Expand Up @@ -1510,4 +1562,3 @@ module cv32e40p_cs_registers
`endif

endmodule

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