Wishbone bridge between Renode and Fomu

This part of the workshop is based on a Renode, Fomu and Etherbone bridge example from the Renode documentation.

Just like we can access Fomu peripherals using wishbone-tool, we can also connect to a physical board from Renode, mapping a part of the memory space to be accessible via the Etherbone protocol.

This is a very useful capability as it enables us to potentially simulate an advanced LiteX SoC system which would not normally fit in the FPGA (or e.g. take a long time to synthesize), and interface it with the remaining part of the physical system for I/O.

Setting up the server

You can use wishbone-tool to bridge protocols such as USB to Etherbone. To start the server, run the following command:

 wishbone-tool -s wishbone

This starts an Etherbone server on localhost:1234 by default. See wishbone-tool --help to change these settings.

Now you can start Renode and setup the platform.

Connecting from Renode

Run renode and in the Monitor type:

(monitor) include @scripts/complex/fomu/renode_etherbone_fomu.resc
(machine-0) start
Starting emulation...
(machine-0) sysbus LogPeripheralAccess sysbus.led

You see a new window with a shell application, that provides additional commands allowing you to control LEDs on Fomu.

 led_toggle
 led_breathe

The led_toggle command controls the LED by turning it on and off. led_breathe makes the LED fade slowly in and out, creating a “breathe” effect.

The script you loaded configures Renode to log all communication with Fomu. After issuing some commands in Zephyr’s shell you’ll see:

01:00:31.8276 [DEBUG] led: [cpu: 0x40000988] WriteUInt32 to 0x8 (unknown), value 0x7.
01:00:31.8279 [DEBUG] led: [cpu: 0x40000990] WriteUInt32 to 0x4 (unknown), value 0x8.
01:00:31.8290 [DEBUG] led: [cpu: 0x40000998] WriteUInt32 to 0x0 (unknown), value 0xC8.
01:00:31.8298 [DEBUG] led: [cpu: 0x400009A0] WriteUInt32 to 0x4 (unknown), value 0x9.
01:00:31.8301 [DEBUG] led: [cpu: 0x400009A8] WriteUInt32 to 0x0 (unknown), value 0xBA.
01:00:31.8305 [DEBUG] led: [cpu: 0x400009B0] WriteUInt32 to 0x8 (unknown), value 0x6.
01:00:31.8308 [DEBUG] led: [cpu: 0x400009B4] WriteUInt32 to 0x8 (unknown), value 0x7.
01:00:31.8311 [DEBUG] led: [cpu: 0x400009BC] WriteUInt32 to 0x4 (unknown), value 0x5.
01:00:31.8314 [DEBUG] led: [cpu: 0x400009C0] WriteUInt32 to 0x0 (unknown), value 0x0.
01:00:31.8317 [DEBUG] led: [cpu: 0x400009C4] WriteUInt32 to 0x4 (unknown), value 0x6.
01:00:31.8321 [DEBUG] led: [cpu: 0x400009C8] WriteUInt32 to 0x0 (unknown), value 0x0.
01:00:31.8324 [DEBUG] led: [cpu: 0x400009D0] WriteUInt32 to 0x4 (unknown), value 0x2.
01:00:31.8327 [DEBUG] led: [cpu: 0x400009D4] WriteUInt32 to 0x0 (unknown), value 0x0.
01:00:31.8331 [DEBUG] led: [cpu: 0x400009DC] WriteUInt32 to 0x4 (unknown), value 0x3.
01:00:31.8334 [DEBUG] led: [cpu: 0x400009E0] WriteUInt32 to 0x0 (unknown), value 0x0.
01:00:31.8337 [DEBUG] led: [cpu: 0x400009E8] WriteUInt32 to 0x4 (unknown), value 0x1.
01:00:31.8341 [DEBUG] led: [cpu: 0x400009F4] WriteUInt32 to 0x0 (unknown), value 0xFF.
01:00:31.8344 [DEBUG] led: [cpu: 0x40000A08] WriteUInt32 to 0x4 (unknown), value 0xA.
01:00:31.8347 [DEBUG] led: [cpu: 0x40000A0C] WriteUInt32 to 0x0 (unknown), value 0x0.
01:00:31.8350 [DEBUG] led: [cpu: 0x40000A14] WriteUInt32 to 0x4 (unknown), value 0xB.
01:00:31.8353 [DEBUG] led: [cpu: 0x40000A18] WriteUInt32 to 0x0 (unknown), value 0xFF.

You can interact with Fomu manually, via the Monitor. To do that, you first need to find the name of the peripheral that serves the connection to Fomu.

Type in peripherals to see a list of all the elements of the emulated SoC. Look for EtherBoneBridge entry:

(machine-0) peripherals
Available peripherals:
  sysbus (SystemBus)
  │
  ├── cpu (VexRiscv)
  │     Slot: 0
  │
  ├── ddr (MappedMemory)
  │     <0x40000000, 0x4FFFFFFF>
  │     <0xC0000000, 0xCFFFFFFF>
  │
  ├── eth (LiteX_Ethernet)
  │   │ <0x60007800, 0x600078FF>
  │   │ <0xE0007800, 0xE00078FF>
  │   │ <0x30000000, 0x30001FFF>
  │   │ <0xB0000000, 0xB0001FFF>
  │   │ <0x60007000, 0x600077FF>
  │   │ <0xE0007000, 0xE00077FF>
  │   │
  │   └── phy (EthernetPhysicalLayer)
  │         Address: 0
  │
  ├── flash_mem (MappedMemory)
  │     <0x20000000, 0x21FFFFFF>
  │     <0xA0000000, 0xA1FFFFFF>
  │
  ├── led (EtherBoneBridge)
  │     <0xE0006800, 0xE00068FF>
  │
  ├── mem (MappedMemory)
  │     <0x00000000, 0x0003FFFF>
  │     <0x80000000, 0x8003FFFF>
  │
  ├── spi (LiteX_SPI_Flash)
  │   │ <0x60005000, 0x6000500F>
  │   │ <0xE0005000, 0xE000500F>
  │   │
  │   └── flash (Micron_MT25Q)
  │
  ├── sram (MappedMemory)
  │     <0x10000000, 0x1003FFFF>
  │     <0x90000000, 0x9003FFFF>
  │
  ├── timer0 (LiteX_Timer)
  │     <0x60002800, 0x60002843>
  │     <0xE0002800, 0xE0002843>
  │
  └── uart (LiteX_UART)
        <0x60001800, 0x600018FF>
        <0xE0001800, 0xE00018FF>

The device that acts as a connector to Fomu is called led and is registered at 0xE0006800:

├── led (EtherBoneBridge)
│     <0xE0006800, 0xE00068FF>

You can either use a full or relative address (via the sysbus or led objects, respectively) to communicate with the physical LED controller:

(machine-0) sysbus WriteDoubleWord 0xE0006804 0x1234 # writes 0x1234 to the given address
(machine-0) led WriteDoubleWord 0x4 0x4321 # writes 0x4321 to 0xE0006800 + 0x4

Note: the above values are just an example and won’t change the LED status in any visible way. If you want to enable “breathe” effect directly from the Monitor, see the necessary sequence in the application source code.