Control and Status Registers

CV32E40P does not implement all control and status registers specified in the RISC-V privileged specifications, but is limited to the registers that were needed for the PULP system. The reason for this is that we wanted to keep the footprint of the core as low as possible and avoid any overhead that we do not explicitly need.

CSR Map

Table 11 lists all implemented CSRs. To columns in Table 11 may require additional explanation:

The Parameter column identifies those CSRs that are dependent on the value of specific compile/synthesis parameters. If these parameters are not set as indicated in Table 11 then the associated CSR is not implemented. If the parameter column is empty then the associated CSR is always implemented.

The Privilege column indicates the access mode of a CSR. The first letter indicates the lowest privilege level required to access the CSR. Attempts to access a CSR with a higher privilege level than the core is currently running in will throw an illegal instruction exception. This is largely a moot point for the CV32E40P as it only supports machine and debug modes. The remaining letters indicate the read and/or write behavior of the CSR when accessed by the indicated or higher privilge level:

• RW: CSR is read-write. That is, CSR instructions (e.g. csrrw) may write any value and that value will be returned on a subsequent read (unless a side-effect causes the core to change the CSR value).

• RO: CSR is read-only. Writes by CSR instructions raise an illegal instruction exception.

Writes of a non-supported value to WLRL bitfields of a RW CSR do not result in an illegal instruction exception. The exact bitfield access types, e.g. WLRL or WARL, can be found in the RISC-V privileged specification.

Reads or writes to a CSR that is not implemented will result in an illegal instruction exception.

Table 11 Control and Status Register Map

CSR Address	Name	Privilege	Parameter	Description
User CSRs
0x001	fflags	URW	FPU = 1	Floating-point accrued exceptions.
0x002	frm	URW	FPU = 1	Floating-point dynamic rounding mode.
0x003	fcsr	URW	FPU = 1	Floating-point control and status register.
0xC00	cycle	URO		(HPM) Cycle Counter
0xC02	instret	URO		(HPM) Instructions-Retired Counter
0xC03	hpmcounter3	URO		(HPM) Performance-Monitoring Counter 3
. . . . .
0xC1F	hpmcounter31	URO		(HPM) Performance-Monitoring Counter 31
0xC80	cycleh	URO		(HPM) Upper 32 Cycle Counter
0xC82	instreth	URO		(HPM) Upper 32 Instructions-Retired Counter
0xC83	hpmcounterh3	URO		(HPM) Upper 32 Performance-Monitoring Counter 3
. . . . .
0xC9F	hpmcounterh31	URO		(HPM) Upper 32 Performance-Monitoring Counter 31
User Custom CSRs
0x800	lpstart0	URW	PULP_XPULP = 1	Hardware Loop 0 Start.
0x801	lpend0	URW	PULP_XPULP = 1	Hardware Loop 0 End.
0x802	lpcount0	URW	PULP_XPULP = 1	Hardware Loop 0 Counter.
0x804	lpstart1	URW	PULP_XPULP = 1	Hardware Loop 1 Start.
0x805	lpend1	URW	PULP_XPULP = 1	Hardware Loop 1 End.
0x806	lpcount1	URW	PULP_XPULP = 1	Hardware Loop 1 Counter.
0xCC0	uhartid	URO	PULP_XPULP = 1	Hardware Thread ID
0xCC1	privlv	URO	PULP_XPULP = 1	Privilege Level
Machine CSRs
0x300	mstatus	MRW		Machine Status
0x301	misa	MRW		Machine ISA
0x304	mie	MRW		Machine Interrupt Enable Register
0x305	mtvec	MRW		Machine Trap-Handler Base Address
0x320	mcountinhibit	MRW		(HPM) Machine Counter-Inhibit Register
0x323	mhpmevent3	MRW		(HPM) Machine Performance-Monitoring Event Selector 3
. . . .
0x33F	mhpmevent31	MRW		(HPM) Machine Performance-Monitoring Event Selector 31
0x340	mscratch	MRW		Machine Scratch
0x341	mepc	MRW		Machine Exception Program Counter
0x342	mcause	MRW		Machine Trap Cause
0x343	mtval	MRW		Machine Trap Value
0x344	mip	MRW		Machine Interrupt Pending Register
0x7A0	tselect	MRW		Trigger Select Register
0x7A1	tdata1	MRW		Trigger Data Register 1
0x7A2	tdata2	MRW		Trigger Data Register 2
0x7A3	tdata3	MRW		Trigger Data Register 3
0x7A4	tinfo	MRO		Trigger Info
0x7A8	mcontext	MRW		Machine Context Register
0x7AA	scontext	MRW		Machine Context Register
0x7B0	dcsr	DRW		Debug Control and Status
0x7B1	dpc	DRW		Debug PC
0x7B2	dscratch0	DRW		Debug Scratch Register 0
0x7B3	dscratch1	DRW		Debug Scratch Register 1
0xB00	mcycle	MRW		(HPM) Machine Cycle Counter
0xB02	minstret	MRW		(HPM) Machine Instructions-Retired Counter
0xB03	mhpmcounter3	MRW		(HPM) Machine Performance-Monitoring Counter 3
. . . .
0xB1F	mhpmcounter31	MRW		(HPM) Machine Performance-Monitoring Counter 31
0xB80	mcycleh	MRW		(HPM) Upper 32 Machine Cycle Counter
0xB82	minstreth	MRW		(HPM) Upper 32 Machine Instructions-Retired Counter
0xB83	mhpmcounterh3	MRW		(HPM) Upper 32 Machine Performance-Monitoring Counter 3
. . . .
0xB9F	mhpmcounterh31	MRW		(HPM) Upper 32 Machine Performance-Monitoring Counter 31
0xF11	mvendorid	MRO		Machine Vendor ID
0xF12	marchid	MRO		Machine Architecture ID
0xF13	mimpid	MRO		Machine Implementation ID
0xF14	mhartid	MRO		Hardware Thread ID

CSR Descriptions

What follows is a detailed definition of each of the CSRs listed above. The Mode column defines the access mode behavior of each bit field when accessed by the privilege level specified in Table 11 (or a higher privilege level):

• RO: read-only fields are not affect by CSR write instructions. Such fields either return a fixed value, or a value determined by the operation of the core.

• RW: read/write fields store the value written by CSR writes. Subsequent reads return either the previously written value or a value determined by the operation of the core.

Floating-point accrued exceptions (fflags)

CSR Address: 0x001 (only present if FPU = 1)

Reset Value: 0x0000_0000

Bit #	Mode	Description
31:5	RO	Writes are ignored; reads return 0.
4	RW	NV- Invalid Operation
3	RW	DZ - Divide by Zero
2	RW	OF - Overflow
1	RW	UF - Underflow
0	RW	NX - Inexact

Floating-point dynamic rounding mode (frm)

CSR Address: 0x002 (only present if FPU = 1)

Reset Value: 0x0000_0000

Bit #	Mode	Description
31:3	RO	Writes are ignored; reads return 0.
2:0	RW	Rounding mode. 000 = RNE, 001 = RTZ, 010 = RDN, 011 = RUP, 100 = RMM 101 = Invalid, 110 = Invalid, 111 = DYN.

Floating-point control and status register (fcsr)

CSR Address: 0x003 (only present if FPU = 1)

Reset Value: 0x0000_0000

Bit #	Mode	Description
31:8	RO	Reserved. Writes are ignored; reads return 0.
7:5	RW	Rounding Mode (frm)
4:0	RW	Accrued Exceptions (fflags)

HWLoop Start Address 0/1 (lpstart0/1)

CSR Address: 0x800/0x804 (only present if PULP_XPULP = 1)

Reset Value: 0x0000_0000

Detailed:

Bit #	Mode	Description
31:0	RW	Start Address of the HWLoop 0/1.

HWLoop End Address 0/1 (lpend0/1)

CSR Address: 0x801/0x805 (only present if PULP_XPULP = 1)

Reset Value: 0x0000_0000

Detailed:

Bit #	Mode	Description
31:0	RW	End Address of the HWLoop 0/1.

HWLoop Count Address 0/1 (lpcount0/1)

CSR Address: 0x802/0x806 (only present if PULP_XPULP = 1)

Reset Value: 0x0000_0000

Detailed:

Bit #	Mode	Description
31:0	RW	Number of iteration of HWLoop 0/1.

Privilege Level (privlv)

CSR Address: 0xCC1 (only present if PULP_XPULP = 1)

Reset Value: 0x0000_0003

Table 13 PRIVLV

Bit #	Mode	Description
31:2	RO	Reads as 0.
1:0	RO	Current Privilege Level. 11 = Machine, 10 = Hypervisor, 01 = Supervisor, 00 = User. CV32E40P only supports Machine mode.

User Hardware Thread ID (uhartid)

CSR Address: 0xCC0 (only present if PULP_XPULP = 1)

Reset Value: Defined

Table 14 UHARTID

Bit #	Mode	Description
31:0	RO	Hardware Thread ID hart_id_i, see Core Integration

Similar to mhartid the uhartid provides the Hardware Thread ID. It differs from mhartid only in the required privilege level. On CV32E40P, as it is a machine mode only implementation, this difference is not noticeable.

Machine Status (mstatus)

CSR Address: 0x300

Reset Value: 0x0000_1800

Bit #	Mode	Description
31:18	RO	Reserved, hardwired to 0
17	RO	MPRV: hardwired to 0
16:13	RO	Unimplemented, hardwired to 0
12:11	RO	MPP: Machine Previous Priviledge mode, hardwired to 11 when the user mode is not enabled.
10:8	RO	Unimplemented, hardwired to 0
7	RO	Previous Machine Interrupt Enable: When an exception is encountered, MPIE will be set to MIE. When the mret instruction is executed, the value of MPIE will be stored to MIE.
6:5	RO	Unimplemented, hardwired to 0
4	RO	Previous User Interrupt Enable: If user mode is enabled, when an exception is encountered, UPIE will be set to UIE. When the uret instruction is executed, the value of UPIE will be stored to UIE.
3	RW	Machine Interrupt Enable: If you want to enable interrupt handling in your exception handler, set the Interrupt Enable MIE to 1 inside your handler code.
2:1	RO	Unimplemented, hardwired to 0
0	RO	User Interrupt Enable: If you want to enable user level interrupt handling in your exception handler, set the Interrupt Enable UIE to 1 inside your handler code.

Machine ISA (misa)

CSR Address: 0x301

Reset Value: defined

Detailed:

Bit #	Mode	Description
31:30	RO (0x1)	MXL (Machine XLEN).
29:26	RO (0x0)	(Reserved).
25	RO (0x0)	Z (Reserved). Read-only; writes are ignored.
24	RO (0x0)	Y (Reserved).
23	RO	X (Non-standard extensions present).
22	RO (0x0)	W (Reserved).
21	RO (0x0)	V (Tentatively reserved for Vector extension).
20	RO (0x0)	U (User mode implemented).
19	RO (0x0)	T (Tentatively reserved for Transactional Memory extension).
18	RO (0x0)	S (Supervisor mode implemented).
17	RO (0x0)	R (Reserved).
16	RO (0x0)	Q (Quad-precision floating-point extension).
15	RO (0x0)	P (Tentatively reserved for Packed-SIMD extension).
14	RO (0x0)	O (Reserved).
13	RO (0x0)	N (User-level interrupts supported).
12	RO (0x1)	M (Integer Multiply/Divide extension).
11	RO (0x0)	L (Tentatively reserved for Decimal Floating-Point extension).
10	RO (0x0)	K (Reserved).
9	RO (0x0)	J (Tentatively reserved for Dynamically Translated Languages extension).
8	RO (0x1)	I (RV32I/64I/128I base ISA).
7	RO (0x0)	H (Hypervisor extension).
6	RO (0x0)	G (Additional standard extensions present).
5	RO	F (Single-precision floating-point extension).
4	RO (0x0)	E (RV32E base ISA).
3	RO (0x0)	D (Double-precision floating-point extension).
2	RO (0x1)	C (Compressed extension).
1	RO (0x0)	B (Tentatively reserved for Bit-Manipulation extension).
0	RO (0x0)	A (Atomic extension).

All bitfields in the misa CSR read as 0 except for the following:

• C = 1

• F = 1 if FPU = 1

• I = 1

• M = 1

• X = 1 if PULP_XPULP = 1 or PULP_CLUSTER = 1

• MXL = 1 (i.e. XLEN = 32)

Machine Interrupt Enable Register (mie)

CSR Address: 0x304

Reset Value: 0x0000_0000

Detailed:

Bit #	Mode	Description
31:16	RW	Machine Fast Interrupt Enables: Set bit x to enable interrupt irq_i[x].
11	RW	Machine External Interrupt Enable (MEIE): If set, irq_i[11] is enabled.
7	RW	Machine Timer Interrupt Enable (MTIE): If set, irq_i[7] is enabled.
3	RW	Machine Software Interrupt Enable (MSIE): if set, irq_i[3] is enabled.

Machine Trap-Vector Base Address (mtvec)

CSR Address: 0x305

Reset Value: Defined

Detailed:

Bit #	Mode	Description
31 : 8	RW	BASE[31:8]: The trap-handler base address, always aligned to 256 bytes.
7 : 2	RO	BASE[7:2]: The trap-handler base address, always aligned to 256 bytes, i.e., mtvec[7:2] is always set to 0.
1	RO	MODE[1]: always 0
0	RW	MODE[0]: 0 = direct mode, 1 = vectored mode.

The initial value of mtvec is equal to {mtvec_addr_i[31:8], 6’b0, 2’b01}.

When an exception or an interrupt is encountered, the core jumps to the corresponding handler using the content of the MTVEC[31:8] as base address. Only 8-byte aligned addresses are allowed. Both direct mode and vectored mode are supported.

Machine Counter-Inhibit Register (mcountinhibit)

CSR Address: 0x320

Reset Value: 0x0000_000D

The performance counter inhibit control register. The default value is to inihibit counters out of reset. The bit returns a read value of 0 for non implemented counters. This reset value shows the result using the default number of performance counters to be 1.

Detailed:

Bit#	Mode	Description
31:4	RW	Dependent on number of counters implemented in design parameter
3	RW	selectors: mhpmcounter3 inhibit
2	RW	minstret inhibit
1	RO	0
0	RW	mcycle inhibit

Machine Performance Monitoring Event Selector (mhpmevent3 .. mhpmevent31)

CSR Address: 0x323 - 0x33F

Reset Value: 0x0000_0000

Detailed:

Bit#	Mode	Description
31:16	RO	0
15:0	RW	selectors: Each bit represent a unique event to count

The event selector fields are further described in Performance Counters section. Non implemented counters always return a read value of 0.

Machine Scratch (mscratch)

CSR Address: 0x340

Reset Value: 0x0000_0000

Detailed:

Bit #	Mode	Description
31:0	RW	Scratch value

Machine Exception PC (mepc)

CSR Address: 0x341

Reset Value: 0x0000_0000

Bit #	Mode	Description
31:1	RW	Machine Expection Program Counter 31:1
0	R0	Always 0

When an exception is encountered, the current program counter is saved in MEPC, and the core jumps to the exception address. When a mret instruction is executed, the value from MEPC replaces the current program counter.

Machine Cause (mcause)

CSR Address: 0x342

Reset Value: 0x0000_0000

Bit #	Mode	Description
31	RW	Interrupt: This bit is set when the exception was triggered by an interrupt.
30:5	RO (0)	Always 0
4:0	RW	Exception Code (See note below)

NOTE: software accesses to mcause[4:0] must be sensitive to the WLRL field specification of this CSR. For example, when mcause[31] is set, writing 0x1 to mcause[1] (Supervisor software interrupt) will result in UNDEFINED behavior.

Machine Trap Value (mtval)

CSR Address: 0x343

Reset Value: 0x0000_0000

Detailed:

Bit #	Mode	Description
31:0	RO (0)	Writes are ignored; reads return 0.

Machine Interrupt Pending Register (mip)

CSR Address: 0x344

Reset Value: 0x0000_0000

Detailed:

Bit #	Mode	Description
31:16	RO	Machine Fast Interrupts Pending: If bit x is set, interrupt irq_i[x] is pending.
11	RO	Machine External Interrupt Pending (MEIP): If set, irq_i[11] is pending.
7	RO	Machine Timer Interrupt Pending (MTIP): If set, irq_i[7] is pending.
3	RO	Machine Software Interrupt Pending (MSIP): if set, irq_i[3] is pending.

Trigger Select Register (tselect)

CSR Address: 0x7A0

Reset Value: 0x0000_0000

Accessible in Debug Mode or M-Mode.

Bit #	Mode	Description
31:0	RO	CV32E40P implements a single trigger, therefore this register will always read as zero

Trigger Data Register 1 (tdata1)

CSR Address: 0x7A1

Reset Value: 0x2800_1040

Accessible in Debug Mode or M-Mode. Since native triggers are not supported, writes to this register from M-Mode will be ignored.

Note

CV32E40P only implements one type of trigger, Match Control. Most fields of this register will read as a fixed value to reflect the single mode that is supported, in particular, instruction address match as described in the Debug Specification 0.13.2 section 5.2.2 & 5.2.9. The type, dmode, hit, select, timing, sizelo, action, chain, match, m, s, u, store and load bitfields of this CSR, which are marked as R/W in Debug Specification 0.13.2, are therefore implemented as WARL bitfields (corresponding to how these bitfields will be specified in the forthcoming Debug Specification 0.14.0).

Bit#	Mode	Description
31:28	RO (0x2)	type: 2 = Address/Data match trigger type.
27	RO (0x1)	dmode: 1 = Only debug mode can write tdata registers
26:21	RO (0x0)	maskmax: 0 = Only exact matching supported.
20	RO (0x0)	hit: 0 = Hit indication not supported.
19	RO (0x0)	select: 0 = Only address matching is supported.
18	RO (0x0)	timing: 0 = Break before the instruction at the specified address.
17:16	RO (0x0)	sizelo: 0 = Match accesses of any size.
15:12	RO (0x1)	action: 1 = Enter debug mode on match.
11	RO (0x0)	chain: 0 = Chaining not supported.
10:7	RO (0x0)	match: 0 = Match the whole address.
6	RO (0x1)	m: 1 = Match in M-Mode.
5	RO (0x0)	zero.
4	RO (0x0)	s: 0 = S-Mode not supported.
3	RO (0x0)	u: 0 = U-Mode not supported.
2	RW	execute: Enable matching on instruction address.
1	RO (0x0)	store: 0 = Store address / data matching not supported.
0	RO (0x0)	load: 0 = Load address / data matching not supported.

Trigger Data Register 2 (tdata2)

CSR Address: 0x7A2

Reset Value: 0x0000_0000

Detailed:

Bit#	Mode	Description
31:0	RO	data

Accessible in Debug Mode or M-Mode. Since native triggers are not supported, writes to this register from M-Mode will be ignored. This register stores the instruction address to match against for a breakpoint trigger.

Trigger Data Register 3 (tdata3)

CSR Address: 0x7A3

Reset Value: 0x0000_0000

Detailed:

Bit#	Mode	Description
31:0	RO	0

Accessible in Debug Mode or M-Mode. CV32E40P does not support the features requiring this register. Writes are ignored and reads will always return zero.

Trigger Info (tinfo)

CSR Address: 0x7A4

Reset Value: 0x0000_0004

Detailed:

Bit#	Mode	Description
31:16	RO (0x0)	0
15:0	RO (0x4)	info. Only type 2 is supported.

The info field contains one bit for each possible type enumerated in tdata1. Bit N corresponds to type N. If the bit is set, then that type is supported by the currently selected trigger. If the currently selected trigger does not exist, this field contains 1.

Accessible in Debug Mode or M-Mode.

Machine Context Register (mcontext)

CSR Address: 0x7A8

Reset Value: 0x0000_0000

Detailed:

Bit#	Mode	Description
31:0	RO	0

Accessible in Debug Mode or M-Mode. CV32E40P does not support the features requiring this register. Writes are ignored and reads will always return zero.

Supervisor Context Register (scontext)

CSR Address: 0x7AA

Reset Value: 0x0000_0000

Detailed:

Bit#	Mode	Description
31:0	RO	0

Accessible in Debug Mode or M-Mode. CV32E40P does not support the features requiring this register. Writes are ignored and reads will always return zero.

Debug Control and Status (dcsr)

CSR Address: 0x7B0

Reset Value: 0x4000_0003

Note

The ebreaks, ebreaku and prv bitfields of this CSR are marked as R/W in Debug Specification 0.13.2. However, as CV32E40P only supports machine mode, these bitfields are implemented as WARL bitfields (corresponding to how these bitfields will be specified in the forthcoming Debug Specification 0.14.0).

Detailed:

Bit #	Mode	Description
31:28	RO (0x4)	xdebugver: returns 4 - External debug support exists as it is described in this document.
27:16	RO (0x0)	Reserved
15	RW	ebreakm
14	RO (0x0)	Reserved
13	RO (0x0)	ebreaks. Always 0.
12	RO (0x0)	ebreaku. Always 0.
11	RW	stepie
10	RO (0x0)	stopcount. Always 0.
9	RO (0x0)	stoptime. Always 0.
8:6	RO	cause
5	RO (0x0)	Reserved
4	RO (0x0)	mprven. Always 0.
3	RO (0x0)	nmip. Always 0.
2	RW	step
1:0	RO (0x3)	prv: returns the current priviledge mode

Debug PC (dpc)

CSR Address: 0x7B1

Reset Value: 0x0000_0000

Detailed:

Bit #	Mode	Description
31:1	RO	zero
0	RO	DPC

When the core enters in Debug Mode, DPC contains the virtual address of the next instruction to be executed.

Debug Scratch Register 0/1 (dscratch0/1)

CSR Address: 0x7B2/0x7B3

Reset Value: 0x0000_0000

Detailed:

Bit #	Mode	Description
31:0	RW	DSCRATCH0/1

Machine Cycle Counter (mcycle)

CSR Address: 0xB00

Reset Value: 0x0000_0000

Detailed:

Bit#	Mode	Description
31:0	RW	The lower 32 bits of the 64 bit machine mode cycle counter.

Machine Instructions-Retired Counter (minstret)

CSR Address: 0xB02

Reset Value: 0x0000_0000

Detailed:

Bit#	Mode	Description
31:0	RW	The lower 32 bits of the 64 bit machine mode instruction retired counter.

Machine Performance Monitoring Counter (mhpmcounter3 .. mhpmcounter31)

CSR Address: 0xB03 - 0xB1F

Reset Value: 0x0000_0000

Detailed:

Bit#	Mode	Description
31:0	RW	Machine performance-monitoring counter

The lower 32 bits of the 64 bit machine performance-monitoring counter(s). The number of machine performance-monitoring counters is determined by the parameter NUM_MHPMCOUNTERS with a range from 0 to 29 (default value of 1). Non implemented counters always return a read value of 0.

Upper 32 Machine Cycle Counter (mcycleh)

CSR Address: 0xB80

Reset Value: 0x0000_0000

Detailed:

Bit#	Mode	Description
31:0	RW	The upper 32 bits of the 64 bit machine mode cycle counter.

Upper 32 Machine Instructions-Retired Counter (minstreth)

CSR Address: 0xB82

Reset Value: 0x0000_0000

Detailed:

Bit#	Mode	Description
31:0	RW	The upper 32 bits of the 64 bit machine mode instruction retired counter.

Upper 32 Machine Performance Monitoring Counter (mhpmcounter3h .. mhpmcounter31h)

CSR Address: 0xB83 - 0xB9F

Reset Value: 0x0000_0000

Detailed:

Bit#	Mode	Description
31:0	RW	Machine performance-monitoring counter

The upper 32 bits of the 64 bit machine performance-monitoring counter(s). The number of machine performance-monitoring counters is determined by the parameter NUM_MHPMCOUNTERS with a range from 0 to 29 (default value of 1). Non implemented counters always return a read value of 0.

Machine Vendor ID (mvendorid)

CSR Address: 0xF11

Reset Value: 0x0000_0602

Detailed:

Bit #	Mode	Description
31:7	RO	0xC. Number of continuation codes in JEDEC manufacturer ID.
6:0	RO	0x2. Final byte of JEDEC manufacturer ID, discarding the parity bit.

The mvendorid encodes the OpenHW JEDEC Manufacturer ID, which is 2 decimal (bank 13).

Machine Architecture ID (marchid)

CSR Address: 0xF12

Reset Value: 0x0000_0004

Detailed:

Bit #	Mode	Description
31:0	RO	Machine Architecture ID of CV32E40P is 4

Machine Implementation ID (mimpid)

CSR Address: 0xF13

Reset Value: 0x0000_0000

Detailed:

Bit #	Mode	Description
31:0	RO	Reads return 0.

Hardware Thread ID (mhartid)

CSR Address: 0xF14

Reset Value: Defined

Bit #	Mode	Description
31:0	RO	Hardware Thread ID hart_id_i, see Core Integration

NOTE: software accesses to ucause[4:0] must be sensitive to the WLRL field specification of this CSR. For example, when ucause[31] is set, writing 0x1 to ucause[1] (Supervisor software interrupt) will result in UNDEFINED behavior.

Cycle Counter (cycle)

CSR Address: 0xC00

Reset Value: 0x0000_0000

Detailed:

Bit#	R/W	Description
31:0	R	0

Read-only unprivileged shadow of the lower 32 bits of the 64 bit machine mode cycle counter.

Instructions-Retired Counter (instret)

CSR Address: 0xC02

Reset Value: 0x0000_0000

Detailed:

Bit#	R/W	Description
31:0	R	0

Read-only unprivileged shadow of the lower 32 bits of the 64 bit machine mode instruction retired counter.

Performance Monitoring Counter (hpmcounter3 .. hpmcounter31)

CSR Address: 0xC03 - 0xC1F

Reset Value: 0x0000_0000

Detailed:

Bit#	R/W	Description
31:0	R	0

Read-only unprivileged shadow of the lower 32 bits of the 64 bit machine mode performance counter. Non implemented counters always return a read value of 0.

Upper 32 Cycle Counter (cycleh)

CSR Address: 0xC80

Reset Value: 0x0000_0000

Detailed:

Bit#	R/W	Description
31:0	R	0

Read-only unprivileged shadow of the upper 32 bits of the 64 bit machine mode cycle counter.

Upper 32 Instructions-Retired Counter (instreth)

CSR Address: 0xC82

Reset Value: 0x0000_0000

Detailed:

Bit#	R/W	Description
31:0	R	0

Read-only unprivileged shadow of the upper 32 bits of the 64 bit machine mode instruction retired counter.

Upper 32 Performance Monitoring Counter (hpmcounter3h .. hpmcounter31h)

CSR Address: 0xC83 - 0xC9F

Reset Value: 0x0000_0000

Detailed:

Bit#	R/W	Description
31:0	R	0

Read-only unprivileged shadow of the upper 32 bits of the 64 bit machine mode performance counter. Non implemented counters always return a read value of 0.