Pico-Pi i.MX7D - Android Things IoT Development Platform

Overview

The i.MX7D SoC is a Hybrid multi-core processor composed of Single Cortex A7 core and Single Cortex M4 core. Zephyr was ported to run on the M4 core. In a later release, it will also communicate with the A7 core (running Linux) via RPmsg.

Pico-Pi i.MX7D

Hardware

The Pico-Pi Platform is composed of a CPU and IO board.

Pico-Pi IO Board

  • S1 - On/Off (MX7_ONOFF signal)
  • Board to board connector : Edison compatible connector (70 configurable pins)
  • mikroBUS expansion connector ADC, GPIO, I²C, PWM, SPI, UART)
  • 10-pin needle JTAG Connector
  • Debug USB exposing One UART
  • MIPI DSI 1 lane Connector
  • LCD Touch Connector
  • Audio Jack: Mic and Stereo Headphone

Pico-Pi CPU Board

  • CPU i.MX7 Dual with a Single Cortex A7 (1 GHz) core and Single Cortex M4 (200MHz) core
  • Memory
    • RAM -> A7: 4GB
    • RAM -> M4: 3x32KB (TCML, TCMU, OCRAM_S), 1x128KB (OCRAM) and 1x256MB (DDR)
    • Flash -> A7: 8GB eMMC

For more information about the i.MX7 SoC and Pico-Pi i.MX7D, see these references:

Supported Features

The Pico-Pi i.MX7D configuration supports the following hardware features on the Cortex M4 Core:

Interface Controller Driver/Component
NVIC on-chip nested vector interrupt controller
SYSTICK on-chip systick
GPIO on-chip gpio
I2C on-chip i2c
UART on-chip serial port-polling; serial port-interrupt

The default configuration can be found in the defconfig file: boards/arm/pico_pi_m4/pico_pi_m4_defconfig

Other hardware features are not currently supported by the port.

Connections and IOs

The Pico-Pi board Board was tested with the following pinmux controller configuration.

Board Name SoC Name Usage
UART_TX232 UART1_TX UART Console
UART_RX232 UART1_RX UART Console
RX_E UART6_TX UART (mikroBUS and Edison)
TX_E UART6_RX UART (mikroBUS and Edison)
I2CX_SDA_3V I2C1_SDA I2C (mikroBUS and Edison)
I2CX_SCL_3V I2C1_SCL I2C (mikroBUS and Edison)

System Clock

The M4 Core is configured to run at a 200 MHz clock speed.

Serial Port

The iMX7D SoC has seven UARTs. The number 6 is configured for the console and the number 2 is used in the mikroBUS connector.

Programming and Debugging

The Pico-Pi i.MX7D doesn’t have QSPI flash for the M4 and it needs to be started by the A7 core. The A7 core is responsible to load the M4 binary application into the RAM, put the M4 in reset, set the M4 Program Counter and Stack Pointer, and get the M4 out of reset. The A7 can perform these steps at bootloader level or after the Linux system has booted.

The M4 can use up to 5 different RAMs. These are the memory mapping for A7 and M4:

Region Cortex-A7 Cortex-M4 (System Bus) Cortex-M4 (Code Bus) Size
DDR 0x80000000-0xFFFFFFFF 0x80000000-0xDFFFFFFF 0x10000000-0x1FFEFFFF 2048MB (less for M4)
OCRAM 0x00900000-0x0091FFFF 0x20200000-0x2021FFFF 0x00900000-0x0091FFFF 128KB
TCMU 0x00800000-0x00807FFF 0x20000000-0x20007FFF   32KB
TCML 0x007F8000-0x007FFFFF   0x1FFF8000-0x1FFFFFFF 32KB
OCRAM_S 0x00180000-0x00187FFF 0x20180000-0x20187FFF 0x00000000-0x00007FFF 32KB

References

At compilation time you have to choose which RAM will be used. This configuration is done in the file boards/arm/pico_pi_m4/pico_pi_m4.dts with “zephyr,flash” (when CONFIG_XIP=y) and “zephyr,sram” properties. The available configurations are:

"zephyr,flash"
- &ddr_code
- &tcml_code
- &ocram_code
- &ocram_s_code
- &ocram_pxp_code
- &ocram_epdc_code

"zephyr,sram"
- &ddr_sys
- &tcmu_sys
- &ocram_sys
- &ocram_s_sys
- &ocram_pxp_sys
- &ocram_epdc_sys

Below you will find the instructions to load and run Zephyr on M4 from A7 using u-boot.

Connect both micro USB interfaces into the PC. This is the A7 console and the UART6 in the Edison connector is M4 console for Zephyr with both configured to work at 115200 8N1. The USB interface is used to power the CPU and IO boards and is connected to the USB OTG interface of the i.MX7D.

After powering up the platform stop the u-boot execution on the A7 core and expose the eMMC as mass storage with the following command in the u-boot prompt: ums 0 mmc 0. Copy the compiled zephyr.bin to the first FAT partition and remove the mounted device on the PC by issuing a “Ctrl+C” in the u-boot prompt. Set the u-boot environment variables and run the zephyr.bin from the appropriated memory configured in the Zephyr compilation:

setenv bootm4 'fatload mmc 0:1 $m4addr $m4fw && dcache flush && bootaux $m4addr'
# TCML
setenv m4tcml 'setenv m4fw zephyr.bin; setenv m4addr 0x007F8000'
setenv bootm4tcml 'run m4tcml && run bootm4'
run bootm4tcml
# TCMU
setenv m4tcmu 'setenv m4fw zephyr.bin; setenv m4addr 0x00800000'
setenv bootm4tcmu 'run m4tcmu && run bootm4'
run bootm4tcmu
# OCRAM
setenv m4ocram 'setenv m4fw zephyr.bin; setenv m4addr 0x00900000'
setenv bootm4ocram 'run m4ocram && run bootm4'
run bootm4ocram
# OCRAM_S
setenv m4ocrams 'setenv m4fw zephyr.bin; setenv m4addr 0x00180000'
setenv bootm4ocrams 'run m4ocrams && run bootm4'
run bootm4ocrams
# DDR
setenv m4ddr 'setenv m4fw zephyr.bin; setenv m4addr 0x80000000'
setenv bootm4ddr 'run m4ddr && run bootm4'
run bootm4ddr

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