Simple machine mode program to probe RISC-V control and status registers.
riscv-probe currently builds for Spike, QEMU and the SiFive E21 core. riscv-probe is a testing tool designed be used to compare CSRs (Control and Status Registers) between mutliple RISC-V simulators and RISC-V hardware implementations.
riscv-probe contains libfemto which is a lightweight bare-metal C library conforming to a reduced set ot the POSIX.1-2017 / IEEE 1003.1-2017 standard. libfemto can be used as a starting point for bare metal RISC-V programs that require interrupt handling, basic string routines and printf.
A recent version of riscv-tools with a multilib build of RISC-V GCC.
The build system uses CROSS_COMPILE as the toolchain prefix and expects
the toolchain to be present in the PATH environment variable. The default
value for CROSS_COMPILE is riscv64-unknown-elf- however this can be
overridden e.g. make CROSS_COMPILE=riscv64-unknown-linux-gnu-. The build
system expects a multilib toolchain as it uses the same toolchain to build
for riscv32 and riscv64. Make sure to use --enable-multilib when
configuring riscv-gnu-toolchain.
The examples are all built with -nostartfiles -nostdlib -nostdinc so either
the RISC-V GCC Newlib toolchain or RISC-V GCC Glibc Linux toolchain can be used.
To build the examples after environent setup, type:
make
To invoke the probe example in spike and RISC-V QEMU:
$ spike --isa=RV32IMAFDC build/bin/rv32imac/spike/probe$ spike --isa=RV64IMAFDC build/bin/rv64imac/spike/probe$ qemu-system-riscv32 -nographic -machine spike -kernel build/bin/rv32imac/spike/probe-bios none$ qemu-system-riscv64 -nographic -machine spike -kernel build/bin/rv64imac/spike/probe-bios none$ qemu-system-riscv32 -nographic -machine virt -kernel build/bin/rv32imac/virt/probe-bios none$ qemu-system-riscv64 -nographic -machine virt -kernel build/bin/rv64imac/virt/probe-bios none$ qemu-system-riscv32 -nographic -machine sifive_e -kernel build/bin/rv32imac/qemu-sifive_e/probe-bios none$ qemu-system-riscv64 -nographic -machine sifive_e -kernel build/bin/rv64imac/qemu-sifive_e/probe-bios none$ qemu-system-riscv32 -nographic -machine sifive_u -kernel build/bin/rv32imac/qemu-sifive_u/probe-bios none$ qemu-system-riscv64 -nographic -machine sifive_u -kernel build/bin/rv64imac/qemu-sifive_u/probe-bios none
libfemto is a lightweight bare-metal C library for embedded RISC-V development. libfemto provides:
- Reduced set of the POSIX.1-2017 / IEEE 1003.1-2017 standard
- Simple lightweight hardware configuration mechanism
- RISC-V machine mode functions and macros
- Console and power device drivers
libfemto implements a reduced set of the POSIX.1-2017 / IEEE 1003.1-2017
standard, with the addition of glibc's getauxval API to access hardware
configuration in an auxiliary vector (__auxv) that contains tuples
describing the target environment. The auxiliary vector is intended as a
lightweight mechanism to pass dynamic configuration information on embedded
targets, serving as an alternative to compile time constants used during
hardware initialization. The auxiliary vector API has been repurposed to
allow retrieval of hardware configuration parameters such as clock
frequencies and device base addresses for use as a compact alternative to
(DTB) Device Tree Binary, which is not available on small embedded targets.
libfemto contains the following device drivers:
- HTIF (Host Target Interface)
- NS16550A UART Console
- SiFive UART Console
- SiFive Test Device
- Semihosting Syscalls
This project contains a simple build system that allows building applications targeting multiple embedded environments. A distinguishing characteristic of the build system is that program objects do not need to be recompiled to target a different environment, rather they are relinked with a different hardware configuration and setup function. The config object causes the correct drivers to be linked via compile time dependencies expressed by symbol references. The following environments are currently supported:
- default - environment where IO defaults to
ebreak - spike- the RISC-V ISA Simulator Golden Model
- virt - the RISC-V VirtIO Virtual Machine
- qemu-sifive_e - QEMU Functional Model of the SiFive E Series
- qemu-sifive_u - QEMU Functional Model of the SiFive U Series
- coreip-e2-arty - SiFive E2 CoreIP Arty A7 FPGA evaluation image
To create a new environment simply add a directory to env with two files:
default.lds- linker script describing the target's memory layoutconfig.c- environment specific configuration
The following is an example configuration from env/<boardname>/config.c
showing the auxiliary vector used by getauxval via the setup function
called by _start before entering main.
auxval_t __auxv[] = {
{ UART0_CLOCK_FREQ, 32000000 },
{ UART0_BAUD_RATE, 115200 },
{ SIFIVE_UART0_CTRL_ADDR, 0x20000000 },
{ SIFIVE_TEST_CTRL_ADDR, 0x4000 },
{ 0, 0 }
};
void setup()
{
/*
* clock setup code should be placed here and should modify the
* uart clock speed before calling register_console, which calls
* uart_init and reads the uart clock speed from the config array.
*/
register_console(&console_sifive_uart);
register_poweroff(&poweroff_sifive_test);
}
The build system automatically includes any directory added to examples
which contains a rules.mk file.
The following is the rules.mk file from the hello example:
$ cat examples/hello/rules.mk
hello_objs = hello.o
and hello.c
$ cat examples/hello/hello.c
#include <stdio.h>
int main(int argc, char **argv)
{
printf("hello\n");
}
libfemto linker scripts define the following special symbols:
| Symbol | Value |
|---|---|
_text_start |
start of .text section |
_text_end |
end of .text section |
_rodata_start |
start of .rodata section |
_rodata_end |
end of .rodata section |
_data_start |
start of .data section |
_data_end |
end of .data section |
_bss_start |
start of .bss section |
_bss_end |
end of .bss section |
_memory_start |
start of RAM |
_memory_end |
end of RAM |
The symbols example program shows how to access these special symbols. They can be used for example to locate data section in a flat image in ROM to copy into memory and to zero the bss section.
Simple example program that sets up PMP (Physical Memory Protection)
to allow all memory accesses and then switches to U mode. The code to
set up PMP to allow all memory access is pmp_allow_all() in machine.h.
The code is derived from bbl.
Note: PMP is enabled by default on systems that implement it, so it is mandatory to include code to configure PMPs to allow memory access when switching from M mode to S mode or U mode, otherwise memory accesses will trap.
Simple enclave example using RISC-V PMP (Physical Memory Protection)
Physical memory protection is enabled for the program text (RX) program data (RW), UART, and the hart is switch to U mode, however, there is only one program and the default trap vector points into the executable text, so traps are handled in M mode, in the same executable text segment.
A future example will load a second process and provide ecall APIs to the process running in the protected enclave.
riscv-probe is a utility that probes the Control and Status Register
address space of a RISC-V emulator, FPGA or board:
$ qemu-system-riscv32 -nographic -machine spike_v1.10 -kernel build/bin/rv32/spike/probe
isa: rv32imafdcsu
csr: fflags illegal_instruction cause=0x00000002 mtval=0x00000000
csr: frm illegal_instruction cause=0x00000002 mtval=0x00000000
csr: fcsr illegal_instruction cause=0x00000002 mtval=0x00000000
csr: mcycle 0xdbfa9cbd
csr: minstret 0xdc03f6a4
csr: mcycleh 0x0007c452
csr: minstreth 0x0007c452
csr: cycle 0xdc1d7e08
csr: time illegal_instruction cause=0x00000002 mtval=0x00000000
csr: instret 0xdc393bf6
csr: cycleh 0x0007c452
csr: timeh illegal_instruction cause=0x00000002 mtval=0x00000000
csr: instreth 0x0007c452
csr: mvendorid 0x00000000
csr: marchid 0x00000000
csr: mimpid 0x00000000
csr: mhartid 0x00000000
csr: mstatus 0x00000000
csr: misa 0x4014112d
csr: medeleg 0x00000000
csr: mideleg 0x00000000
csr: mie 0x00000000
csr: mtvec 0x80000004
csr: mcounteren 0x00000000
csr: mscratch 0x00000000
csr: mepc 0x800002a4
csr: mcause 0x00000002
csr: mtval 0x00000000
csr: mip 0x00000000
csr: sstatus 0x00000000
csr: sedeleg illegal_instruction cause=0x00000002 mtval=0x00000000
csr: sideleg illegal_instruction cause=0x00000002 mtval=0x00000000
csr: sie 0x00000000
csr: stvec 0x00000000
csr: scounteren 0x00000000
csr: sscratch 0x00000000
csr: sepc 0x00000000
csr: scause 0x00000000
csr: stval 0x00000000
csr: sip 0x00000000
csr: satp 0x00000000
csr: pmpcfg0 0x00000000
csr: pmpcfg1 0x00000000
csr: pmpcfg2 0x00000000
csr: pmpcfg3 0x00000000
csr: pmpaddr0 0x00000000
csr: pmpaddr1 0x00000000
csr: pmpaddr2 0x00000000
csr: pmpaddr3 0x00000000
csr: pmpaddr4 0x00000000
csr: pmpaddr5 0x00000000
csr: pmpaddr6 0x00000000
csr: pmpaddr7 0x00000000
csr: pmpaddr8 0x00000000
csr: pmpaddr9 0x00000000
csr: pmpaddr10 0x00000000
csr: pmpaddr11 0x00000000
csr: pmpaddr12 0x00000000
csr: pmpaddr13 0x00000000
csr: pmpaddr14 0x00000000
csr: pmpaddr15 0x00000000
$ qemu-system-riscv64 -nographic -machine spike_v1.10 -kernel build/bin/rv64/spike/probe
isa: rv64imafdcsu
csr: fflags illegal_instruction cause=0x00000002 mtval=0x00000000
csr: frm illegal_instruction cause=0x00000002 mtval=0x00000000
csr: fcsr illegal_instruction cause=0x00000002 mtval=0x00000000
csr: mcycle 0x0007c452dfeeddd3
csr: minstret 0x0007c452dff8a765
csr: mcycleh illegal_instruction cause=0x00000002 mtval=0x00000000
csr: minstreth illegal_instruction cause=0x00000002 mtval=0x00000000
csr: cycle 0x0007c452e01f105f
csr: time illegal_instruction cause=0x00000002 mtval=0x00000000
csr: instret 0x0007c452e03d0a50
csr: cycleh illegal_instruction cause=0x00000002 mtval=0x00000000
csr: timeh illegal_instruction cause=0x00000002 mtval=0x00000000
csr: instreth illegal_instruction cause=0x00000002 mtval=0x00000000
csr: mvendorid 0x0000000000000000
csr: marchid 0x0000000000000000
csr: mimpid 0x0000000000000000
csr: mhartid 0x0000000000000000
csr: mstatus 0x0000000000000000
csr: misa 0x800000000014112d
csr: medeleg 0x0000000000000000
csr: mideleg 0x0000000000000000
csr: mie 0x0000000000000000
csr: mtvec 0x0000000080000004
csr: mcounteren 0x0000000000000000
csr: mscratch 0x0000000000000000
csr: mepc 0x00000000800002f4
csr: mcause 0x0000000000000002
csr: mtval 0x0000000000000000
csr: mip 0x0000000000000000
csr: sstatus 0x0000000000000000
csr: sedeleg illegal_instruction cause=0x00000002 mtval=0x00000000
csr: sideleg illegal_instruction cause=0x00000002 mtval=0x00000000
csr: sie 0x0000000000000000
csr: stvec 0x0000000000000000
csr: scounteren 0x0000000000000000
csr: sscratch 0x0000000000000000
csr: sepc 0x0000000000000000
csr: scause 0x0000000000000000
csr: stval 0x0000000000000000
csr: sip 0x0000000000000000
csr: satp 0x0000000000000000
csr: pmpcfg0 0x0000000000000000
csr: pmpcfg1 0x0000000000000000
csr: pmpcfg2 0x0000000000000000
csr: pmpcfg3 0x0000000000000000
csr: pmpaddr0 0x0000000000000000
csr: pmpaddr1 0x0000000000000000
csr: pmpaddr2 0x0000000000000000
csr: pmpaddr3 0x0000000000000000
csr: pmpaddr4 0x0000000000000000
csr: pmpaddr5 0x0000000000000000
csr: pmpaddr6 0x0000000000000000
csr: pmpaddr7 0x0000000000000000
csr: pmpaddr8 0x0000000000000000
csr: pmpaddr9 0x0000000000000000
csr: pmpaddr10 0x0000000000000000
csr: pmpaddr11 0x0000000000000000
csr: pmpaddr12 0x0000000000000000
csr: pmpaddr13 0x0000000000000000
csr: pmpaddr14 0x0000000000000000
csr: pmpaddr15 0x0000000000000000