# Emulating generic RISC-V 32bit machine on spike

## Requirements

1. GNU RISC-V toolchains (tested on Crosstool-NG)
2. spike from https://github.com/riscv/riscv-isa-sim
3. OpenOCD from https://github.com/riscv/riscv-openocd

## How to build toolchain

Clone the Crosstool-NG and build.

```
$ git clone https://github.com/crosstool-ng/crosstool-ng
$ cd crosstool-ng
$ ./bootstrap
$ ./configure --enable-local
$ make
$ ./ct-ng menuconfig
```

For RV32 builds, change the following configs:

```
CT_EXPERIMENTAL=y
CT_ARCH_RISCV=y
CT_ARCH_64=n
CT_ARCH_ARCH=rv32ima
CT_ARCH_ABI=ilp32
CT_TARGET_CFLAGS="-mcmodel=medany"
CT_TARGET_LDFLAGS="-mcmodel=medany"
CT_MULTILIB=y
CT_DEBUG_GDB=y
```

For RV64 builds, change the following configs:

```
CT_EXPERIMENTAL=y
CT_ARCH_RISCV=y
CT_ARCH_64=y
CT_ARCH_ARCH=rv32ima
CT_ARCH_ABI=ilp32
CT_TARGET_CFLAGS="-mcmodel=medany"
CT_TARGET_LDFLAGS="-mcmodel=medany"
CT_MULTILIB=y
CT_DEBUG_GDB=y
```

Build the GNU toolchain for RISC-V.

```
$ ./ct-ng build
```

A toolchain is installed at ~/x-tools/riscv64-unknown-elf directory.


## How to build

Add path of toolchain that is described above section.

```
$ export PATH=~/x-tools/riscv64-unknown-elf/bin:$PATH
```

To build, simply run `make`. If you want a debug build, pass `DEBUG=1`. If
you want an RV64 build, pass `XLEN=64`.

The resulting executable file is ./build/RTOSDemo32.axf or ./build/RTOSDemo64.axf.

## How to run

RV32:
```
$ spike -p1 --isa RV32IMA -m0x80000000:0x10000000 --rbb-port 9824 \
        ./build/RTOSDemo32.axf
```

RV64:
```
$ spike -p1 --isa RV64IMA -m0x80000000:0x10000000 --rbb-port 9824 \
        ./build/RTOSDemo64.axf
```

## How to debug with gdb

Start OpenOCD in one terminal:
```
$ openocd -f spike-1.cfg
```

Start gdb in another:
```
$ riscv64-unknown-elf-gdb ./build/RTOSDemo.axf
...
(gdb) target extended-remote localhost:3333
...
(gdb) info threads
```

(As of 3/22/2021 OpenOCD's RISC-V FreeRTOS awareness is still incomplete.)

## Description

This demo starts separate transmit and receive threads. The transmit thread sends integers through a queue. Both threads print out what they're sending/receiving using HTIF.