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Phase 2: Linux Boot¶

Objective¶

Boot the full Linux software stack (OpenSBI → U-Boot → Linux Kernel → BusyBox) on the SMVDU-TITAN-X, targeting both simulation (QEMU) and FPGA.

Success Criteria:
✅ OpenSBI initializes and transfers control to U-Boot
✅ U-Boot loads Linux kernel from SD card or memory
✅ Linux kernel boots to BusyBox shell over UART console
✅ Basic commands (ls, cat /proc/cpuinfo) work

Additional Hardware (vs Phase 1)¶

Addition	Details
DDR Controller	LiteDRAM or vendor DRAM IP
DDR Memory	512 MB DDR4 minimum
SRAM (boot)	Kept for initial OpenSBI load

Software Stack¶

BusyBox Shell
     │
Linux Kernel (riscv64, defconfig + titan_x customizations)
     │
OpenSBI (v1.x, generic or smvdu_titan_x platform)
     │
U-Boot (RISC-V port)
     │
SMVDU-TITAN-X Hardware

Step-by-Step¶

1. Build RISC-V Linux Toolchain¶

# The Linux kernel requires a glibc-based toolchain (not elf/newlib)
# Install riscv64-linux-gnu from Ubuntu packages:
sudo apt-get install gcc-riscv64-linux-gnu

# Or use Buildroot's built-in toolchain

2. Build OpenSBI¶

cd software/opensbi
# Initialize the submodule
git submodule update --init

# Build for SMVDU-TITAN-X platform (custom) or generic (quick start)
# Generic first:
make CROSS_COMPILE=riscv64-unknown-elf- PLATFORM=generic FW_PAYLOAD=n

# With TITAN-X platform (after implementing platform.c):
# make CROSS_COMPILE=riscv64-unknown-elf- \
#      PLATFORM=smvdu_titan_x \
#      FW_PAYLOAD_PATH=../uboot/u-boot.bin

3. Build U-Boot¶

cd software/uboot
git submodule update --init

export ARCH=riscv
export CROSS_COMPILE=riscv64-linux-gnu-

# Use QEMU RISC-V virt config to start
make qemu-riscv64_smode_defconfig
make -j$(nproc)

# Output: u-boot.bin, u-boot.elf

4. Build Linux Kernel¶

cd software/linux
git submodule update --init

export ARCH=riscv
export CROSS_COMPILE=riscv64-linux-gnu-

# Start from TITAN-X defconfig
cp arch/riscv/configs/titan_x_defconfig .config
# Or use: make defconfig

make -j$(nproc)

# Output: arch/riscv/boot/Image

5. Build BusyBox rootfs with Buildroot¶

cd software/buildroot
make titan_x_defconfig
make -j$(nproc)

# Output: output/images/rootfs.cpio.gz

6. Test in QEMU First¶

# Validate full stack in QEMU before FPGA
qemu-system-riscv64 \
    -machine virt \
    -cpu rv64 \
    -m 512M \
    -nographic \
    -bios software/opensbi/build/platform/generic/firmware/fw_jump.elf \
    -kernel software/linux/arch/riscv/boot/Image \
    -append "root=/dev/ram rw console=ttyS0" \
    -initrd software/buildroot/output/images/rootfs.cpio.gz

7. Deploy to FPGA¶

Integrate DDR controller (LiteDRAM or Vivado MIG)
Load OpenSBI + kernel image to DDR via JTAG or SD card
Connect serial terminal at 115200 baud
Power on → observe boot sequence

Device Tree¶

A minimal device tree for Phase 2 must describe:

/dts-v1/;

/ {
    #address-cells = <1>;
    #size-cells = <1>;
    compatible = "smvdu,titan-x";
    model = "SMVDU TITAN-X";

    cpus {
        #address-cells = <1>;
        #size-cells = <0>;
        cpu@0 {
            device_type = "cpu";
            reg = <0>;
            status = "okay";
            compatible = "riscv";
            riscv,isa = "rv64imafdc";
            mmu-type = "riscv,sv39";
        };
    };

    memory@80000000 {
        device_type = "memory";
        reg = <0x80000000 0x20000000>; /* 512 MB */
    };

    clint@2000000 {
        compatible = "riscv,clint0";
        interrupts-extended = <&cpu0_intc 3 &cpu0_intc 7>;
        reg = <0x02000000 0x000c0000>;
    };

    plic@c000000 {
        compatible = "sifive,plic-1.0.0";
        reg = <0x0c000000 0x04000000>;
        #interrupt-cells = <1>;
        riscv,ndev = <32>;
    };

    uart@54000000 {
        compatible = "sifive,uart0";
        reg = <0x54000000 0x1000>;
        interrupts = <1>;
        clocks = <&clkc 0>;
    };
};

Expected Boot Log¶

OpenSBI v1.x
   ____                    _____ ____ _____
  / __ \                  / ____|  _ \_   _|
 | |  | |_ __   ___ _ __ | (___ | |_) || |
 | |  | | '_ \ / _ \ '_ \ \___ \|  _ < | |
 | |__| | |_) |  __/ | | |____) | |_) || |_
  \____/| .__/ \___|_| |_|_____/|____/_____|
        | |
        |_|

Platform Name       : SMVDU TITAN-X
...

U-Boot 2024.xx ...

Linux version 6.x.x (riscv64-linux-gnu-gcc ...)
...

Please press Enter to activate this console.

/ # uname -a
Linux titan-x 6.x.x #1 SMP Mon May 26 ... riscv64 GNU/Linux

/ # cat /proc/cpuinfo
processor       : 0
hart            : 0
isa             : rv64imafdc
mmu             : sv39

References¶