# ppce500 generic platform (`ppce500`)

QEMU for PPC supports a special `ppce500` machine designed for emulation and virtualization purposes.

## Supported devices

The `ppce500` machine supports the following devices:

- PowerPC e500 series core (e500v2/e500mc/e5500/e6500)

- Configuration, Control, and Status Register (CCSR)

- Multicore Programmable Interrupt Controller (MPIC) with MSI support

- 1 16550A UART device

- 1 Freescale MPC8xxx I2C controller

- 1 Pericom pt7c4338 RTC via I2C

- 1 Freescale MPC8xxx GPIO controller

- Power-off functionality via one GPIO pin

- 1 Freescale MPC8xxx PCI host controller

- VirtIO devices via PCI bus

- 1 Freescale Enhanced Triple Speed Ethernet controller (eTSEC)

## Hardware configuration information

The `ppce500` machine automatically generates a device tree blob (“dtb”) which it passes to the guest, if there is no `-dtb` option. This provides information about the addresses, interrupt lines and other configuration of the various devices in the system.

If users want to provide their own DTB, they can use the `-dtb` option. These DTBs should have the following requirements:

- The number of subnodes under /cpus node should match QEMU’s `-smp` option

- The /memory reg size should match QEMU’s selected ram_size via `-m`

Both `qemu-system-ppc` and `qemu-system-ppc64` provide emulation for the following 32-bit PowerPC CPUs:

- e500v2

- e500mc

Additionally `qemu-system-ppc64` provides support for the following 64-bit PowerPC CPUs:

- e5500

- e6500

The CPU type can be specified via the `-cpu` command line. If not specified, it creates a machine with e500v2 core. The following example shows an e6500 based machine creation:

    $ qemu-system-ppc64 -nographic -M ppce500 -cpu e6500

## Boot options

The `ppce500` machine can start using the standard -kernel functionality for loading a payload like an OS kernel (e.g.: Linux), or U-Boot firmware.

When -bios is omitted, the default pc-bios/u-boot.e500 firmware image is used as the BIOS. QEMU follows below truth table to select which payload to execute:

-bios | -kernel | payload
--- | --- | ---
N | N | u-boot
N | Y | kernel
Y | don’t care | u-boot

When both -bios and -kernel are present, QEMU loads U-Boot and U-Boot in turns automatically loads the kernel image specified by the -kernel parameter via U-Boot’s built-in “bootm” command, hence a legacy uImage format is required in such scenario.

## Running Linux kernel

Linux mainline v5.11 release is tested at the time of writing. To build a Linux mainline kernel that can be booted by the `ppce500` machine in 64-bit mode, simply configure the kernel using the defconfig configuration:

    $ export ARCH=powerpc
    $ export CROSS_COMPILE=powerpc-linux-
    $ make corenet64_smp_defconfig
    $ make menuconfig

then manually select the following configuration:

> Platform support > Freescale Book-E Machine Type > QEMU generic e500 platform

To boot the newly built Linux kernel in QEMU with the `ppce500` machine:

    $ qemu-system-ppc64 -M ppce500 -cpu e5500 -smp 4 -m 2G \
        -display none -serial stdio \
        -kernel vmlinux \
        -initrd /path/to/rootfs.cpio \
        -append "root=/dev/ram"

To build a Linux mainline kernel that can be booted by the `ppce500` machine in 32-bit mode, use the same 64-bit configuration steps except the defconfig file should use corenet32_smp_defconfig.

To boot the 32-bit Linux kernel:

    $ qemu-system-ppc64 -M ppce500 -cpu e500mc -smp 4 -m 2G \
        -display none -serial stdio \
        -kernel vmlinux \
        -initrd /path/to/rootfs.cpio \
        -append "root=/dev/ram"

## Running U-Boot

U-Boot mainline v2021.07 release is tested at the time of writing. To build a U-Boot mainline bootloader that can be booted by the `ppce500` machine, use the qemu-ppce500_defconfig with similar commands as described above for Linux:

    $ export CROSS_COMPILE=powerpc-linux-
    $ make qemu-ppce500_defconfig

You will get u-boot file in the build tree.

When U-Boot boots, you will notice the following if using with `-cpu e6500`:

    CPU:   Unknown, Version: 0.0, (0x00000000)
    Core:  e6500, Version: 2.0, (0x80400020)

This is because we only specified a core name to QEMU and it does not have a meaningful SVR value which represents an actual SoC that integrates such core. You can specify a real world SoC device that QEMU has built-in support but all these SoCs are e500v2 based MPC85xx series, hence you cannot test anything built for P4080 (e500mc), P5020 (e5500) and T2080 (e6500).

## Networking

By default a VirtIO standard PCI networking device is connected as an ethernet interface at PCI address 0.1.0, but we can switch that to an e1000 NIC by:

    $ qemu-system-ppc64 -M ppce500 -smp 4 -m 2G \
                        -display none -serial stdio \
                        -bios u-boot \
                        -nic tap,ifname=tap0,script=no,downscript=no,model=e1000

The QEMU `ppce500` machine can also dynamically instantiate an eTSEC device if “-device eTSEC” is given to QEMU:

    -netdev tap,ifname=tap0,script=no,downscript=no,id=net0 -device eTSEC,netdev=net0

## Root file system on flash drive

Rather than using a root file system on ram disk, it is possible to have it on CFI flash. Given an ext2 image whose size must be a power of two, it can be used as follows:

    $ qemu-system-ppc64 -M ppce500 -cpu e500mc -smp 4 -m 2G \
        -display none -serial stdio \
        -kernel vmlinux \
        -drive if=pflash,file=/path/to/rootfs.ext2,format=raw \
        -append "rootwait root=/dev/mtdblock0"