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CM33 Firmware Guide

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Alex J Lennon edited this page Sep 9, 2025 · 1 revision

Cortex-M33 Firmware Loading Guide

Board: imx93-jaguar-eink
Target: CM33 firmware development and deployment
Audience: Embedded developers

Overview

The i.MX93 Jaguar E-Ink board supports loading and running firmware on the Cortex-M33 co-processor. This guide covers both U-Boot and Linux kernel methods for CM33 firmware management.

Hardware Configuration

Memory Layout

The CM33 core has access to:

  • TCM (Tightly Coupled Memory): 0x201E0000 - 0x201FFFFF (128KB)
  • System RAM: Shared with A55 cores via reserved memory regions
  • Peripherals: Direct access to many i.MX93 peripherals

Reserved Memory Regions

The device tree configures these memory regions for CM33:

reserved-memory {
    rsc_table: rsc-table@1fff8000 {
        reg = <0 0x1fff8000 0 0x1000>;
        no-map;
    };
    
    vdev0vring0: vdev0vring0@aff00000 {
        reg = <0 0xaff00000 0 0x8000>;
        no-map;
    };
    
    vdev0vring1: vdev0vring1@aff08000 {
        reg = <0 0xaff08000 0 0x8000>;
        no-map;
    };
    
    vdevbuffer: vdevbuffer@a8400000 {
        compatible = "shared-dma-pool";
        reg = <0 0xa8400000 0 0x100000>;
        no-map;
    };
    
    m33_reserved: m33_noncacheable_section@a8600000 {
        no-map;
        reg = <0 0xa8600000 0 0x1000000>;
    };
};

Method 1: U-Boot Firmware Loading

Prerequisites

  • CM33 firmware binary (.bin or .elf format)
  • Firmware stored on SD card, eMMC, or loaded via TFTP

U-Boot Commands

Load and Start CM33 Firmware

# 1. Load firmware from SD card
=> fatload mmc 1:1 ${loadaddr} cm33_firmware.bin

# 2. Copy firmware to CM33 TCM
=> cp.b ${loadaddr} 0x201e0000 ${filesize}

# 3. Start CM33 core
=> bootaux 0x201e0000 0

Alternative: Load ELF Firmware

# Load ELF format firmware (automatically handles memory layout)
=> fatload mmc 1:1 ${loadaddr} cm33_firmware.elf
=> bootelf ${loadaddr}

Environment Variables for Automation

Add these to U-Boot environment for automated CM33 startup:

# Set firmware path and load address
=> setenv cm33_firmware cm33_firmware.bin
=> setenv cm33_loadaddr 0x80000000

# Create boot script for CM33
=> setenv boot_cm33 'fatload mmc 1:1 ${cm33_loadaddr} ${cm33_firmware}; cp.b ${cm33_loadaddr} 0x201e0000 ${filesize}; bootaux 0x201e0000 0'

# Auto-start CM33 during boot
=> setenv bootcmd 'run boot_cm33; run distro_bootcmd'
=> saveenv

U-Boot Configuration

The following U-Boot features are enabled for CM33 support:

  • CONFIG_IMX_BOOTAUX=y - Auxiliary core support
  • CONFIG_CMD_BOOTAUX=y - bootaux command
  • CONFIG_CMD_ELF=y - ELF loading support
  • CONFIG_CMD_MEMORY=y - Memory operations
  • File system support for firmware loading

Method 2: Linux Kernel Remoteproc

Prerequisites

  • CM33 firmware in ELF format
  • Firmware placed in /lib/firmware/
  • Remoteproc kernel support enabled

Kernel Configuration

The following kernel features are enabled:

CONFIG_REMOTEPROC=y
CONFIG_REMOTEPROC_CDEV=y
CONFIG_IMX_REMOTEPROC=y
CONFIG_RPMSG=y
CONFIG_RPMSG_CHAR=y
CONFIG_RPMSG_CTRL=y
CONFIG_RPMSG_NS=y

Runtime Commands

Check Remoteproc Status

# List available remoteproc devices
ls /sys/class/remoteproc/

# Check current state
cat /sys/class/remoteproc/remoteproc0/state
# Possible states: offline, running, crashed, invalid

Load and Start CM33 Firmware

# 1. Copy firmware to /lib/firmware/
cp cm33_firmware.elf /lib/firmware/

# 2. Set firmware name
echo "cm33_firmware.elf" > /sys/class/remoteproc/remoteproc0/firmware

# 3. Start CM33 core
echo "start" > /sys/class/remoteproc/remoteproc0/state

Stop CM33 Core

# Stop CM33 core
echo "stop" > /sys/class/remoteproc/remoteproc0/state

Monitor CM33 Status

# Check remoteproc status
cat /sys/class/remoteproc/remoteproc0/state

# View remoteproc information
cat /sys/class/remoteproc/remoteproc0/name
cat /sys/class/remoteproc/remoteproc0/firmware

# Check kernel messages
dmesg | grep remoteproc
dmesg | grep rpmsg

Inter-Processor Communication (RPMSG)

RPMSG Channels

Once CM33 is running with RPMSG support, communication channels appear:

# List RPMSG devices
ls /dev/rpmsg*

# Example devices:
# /dev/rpmsg_ctrl0 - Control channel
# /dev/rpmsg0 - Data channel

RPMSG Communication Example

# Send data to CM33
echo "Hello CM33" > /dev/rpmsg0

# Read data from CM33
cat /dev/rpmsg0

RPMSG TTY Console

If CM33 firmware supports TTY console:

# Check for RPMSG TTY devices
ls /dev/ttyRPMSG*

# Connect to CM33 console
minicom -D /dev/ttyRPMSG0

Firmware Development

CM33 Firmware Requirements

Your CM33 firmware should:

  1. Link to TCM address: Start at 0x201E0000
  2. Initialize stack pointer: Set up stack in TCM or SRAM
  3. Configure vector table: Set VTOR register
  4. Handle RPMSG: Implement RPMSG protocol for communication

Example Linker Script (cm33.ld)

MEMORY
{
    TCM (rwx) : ORIGIN = 0x201E0000, LENGTH = 128K
    SRAM (rwx) : ORIGIN = 0xA8600000, LENGTH = 16M
}

SECTIONS
{
    .text : {
        . = ALIGN(4);
        *(.vectors)
        *(.text*)
        . = ALIGN(4);
    } > TCM
    
    .data : {
        . = ALIGN(4);
        *(.data*)
        . = ALIGN(4);
    } > TCM
    
    .bss : {
        . = ALIGN(4);
        *(.bss*)
        . = ALIGN(4);
    } > TCM
}

Build Commands

# Compile CM33 firmware
arm-none-eabi-gcc -mcpu=cortex-m33 -mthumb -T cm33.ld -o cm33_firmware.elf main.c

# Convert to binary format for U-Boot
arm-none-eabi-objcopy -O binary cm33_firmware.elf cm33_firmware.bin

Debugging

U-Boot Debugging

# Check if bootaux command is available
=> help bootaux

# Verify firmware loading
=> md.b 0x201e0000 0x100

# Check CM33 core status
=> bootaux 0x201e0000 0
# Should show "## Starting auxiliary core..." message

Linux Debugging

# Check remoteproc driver loading
lsmod | grep remoteproc

# Check device tree CM33 node
cat /proc/device-tree/cm33/status

# Check mailbox devices
ls /sys/class/mailbox/

# Monitor kernel messages during firmware loading
dmesg -w &
echo "start" > /sys/class/remoteproc/remoteproc0/state

Common Issues

Firmware Not Starting:

  1. Check firmware load address (must be 0x201E0000 for TCM)
  2. Verify firmware format (binary for U-Boot, ELF for remoteproc)
  3. Check memory permissions and reserved regions

RPMSG Communication Fails:

  1. Verify CM33 firmware implements RPMSG protocol
  2. Check vring buffer configuration in device tree
  3. Ensure mailbox devices are working

Remoteproc State "crashed":

  1. Check CM33 firmware for exceptions
  2. Verify memory layout and stack configuration
  3. Check for resource table in ELF firmware

Example Use Cases

1. Real-Time Data Processing

Use CM33 for time-critical tasks while A55 handles Linux applications:

# Start real-time firmware
echo "realtime_processor.elf" > /sys/class/remoteproc/remoteproc0/firmware
echo "start" > /sys/class/remoteproc/remoteproc0/state

# Send sensor data to CM33
echo "sensor_data" > /dev/rpmsg0

2. Power Management

Use CM33 for low-power monitoring while A55 cores sleep:

# Load power management firmware
echo "power_manager.elf" > /sys/class/remoteproc/remoteproc0/firmware
echo "start" > /sys/class/remoteproc/remoteproc0/state

3. Peripheral Control

Dedicate CM33 to handle specific peripherals:

# Load peripheral controller firmware
echo "peripheral_ctrl.elf" > /sys/class/remoteproc/remoteproc0/firmware
echo "start" > /sys/class/remoteproc/remoteproc0/state

Integration with Build System

Adding CM33 Firmware to Image

Create a recipe to include CM33 firmware in the root filesystem:

# recipes-bsp/cm33-firmware/cm33-firmware.bb
SUMMARY = "CM33 firmware for imx93-jaguar-eink"
LICENSE = "CLOSED"

SRC_URI = "file://cm33_firmware.elf"

do_install() {
    install -d ${D}/lib/firmware
    install -m 0644 ${WORKDIR}/cm33_firmware.elf ${D}/lib/firmware/
}

FILES:${PN} = "/lib/firmware/cm33_firmware.elf"

Auto-Start CM33 on Boot

Create a systemd service:

# /etc/systemd/system/cm33-autostart.service
[Unit]
Description=Auto-start CM33 firmware
After=multi-user.target

[Service]
Type=oneshot
ExecStart=/bin/sh -c 'echo cm33_firmware.elf > /sys/class/remoteproc/remoteproc0/firmware'
ExecStart=/bin/sh -c 'echo start > /sys/class/remoteproc/remoteproc0/state'
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

Performance Considerations

Memory Access

  • TCM: Fastest access, limited to 128KB
  • SRAM: Good performance, larger capacity
  • DDR: Slowest but largest capacity

Communication Overhead

  • RPMSG: Higher-level protocol, easier to use
  • Shared Memory: Lower overhead, requires synchronization
  • Mailbox: Lowest overhead, interrupt-based

Power Management

  • CM33 can run while A55 cores are in low-power states
  • Implement proper clock gating in CM33 firmware
  • Use WFI instruction when CM33 is idle

For questions or issues, contact the software team with specific error messages and firmware details.

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