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RTOS and AMP

Architecture​

The V821 combines a Linux RISC-V CPU with a RISC-V MCU. Normal and fast-boot boards may load the RTOS from BOOT0/U-Boot, while other designs can manage the MCU through Linux remoteproc.

V821 AMP architecture

RTOS Directories​

rtos/board/v821_e907/          Board configuration
rtos/lichee/rtos/              RTOS kernel and projects
rtos/lichee/rtos-components/   Components
rtos/lichee/rtos-hal/          HAL drivers

Build​

source build/envsetup.sh
lunch
mrtos

Typical output:

rtos/lichee/rtos/build/img/
├── rt_system.bin
├── rt_system.elf
├── rt_system.map
└── rt_system.syms

The SDK copies the runtime image to:

device/config/chips/v821/configs/<board>/bin/amp_rv0.bin

Clean and configure with:

mrtos clean
mrtos menuconfig

Memory Layout​

  • The Linux kernel start address must satisfy 4MB alignment.
  • OpenSBI should remain at a fixed, 128KB-aligned address with PMP protection.
  • RTOS, vring, rpbuf, and no-map reserved areas must not overlap.
  • U-Boot relocates near the end of DRAM, so large reserved regions must not consume that area.

remoteproc​

Board-side checks:

ls /sys/class/remoteproc/
cat /sys/class/remoteproc/remoteproc0/state
echo start > /sys/class/remoteproc/remoteproc0/state
echo stop  > /sys/class/remoteproc/remoteproc0/state

The actual node and start method depend on whether the MCU has already been started by the boot chain. Do not start the same core twice.

Communication​

  • vring: available and used descriptor queues.
  • rpmsg: message channels for control and small payloads.
  • rpbuf: shared large buffers for audio/video data.
  • Interrupt/mailbox: notification of queue or state changes.

Logs and Debugging​

  • amp_shell provides an AMP control console.
  • Trace log retrieves MCU-side messages.
  • Keep rt_system.elf and .map for address symbolization.
  • Investigate stack overflow, double free, shared-buffer overruns, cache coherency, and boot ordering.