thejas32-testbed
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shreekumar3d
Board to test out THEJAS32
Status
We're at v1.0, and the board is being tested out.
Do look at the respective directories for hardware and software.
Intro
CDAC sells the ARIES series of boards based on the THEJAS32 microcontroller. The boards can be programmed using the Arduino IDE. Unfortunately, the schematics of these are not made available. Documentation about the THEJAS32 SoC itself is scarce as well, though the chip itself is available for purchase on robu.in in single quantity.
This project (and follow on work) will try to fill this gap, as I find more. This is a board design for a learner board based on the THEJAS32 microcontroller. It is the first open source board based on the THEJAS32. This is part of a much larger effort to document THEJAS32 and its ecosystem and make it usuable.
THEJAS32 runs directly on an external clock, offering a single core 100 MHz RISC-V CPU with a IO interfaces - UART, SPI, I2C, PWM and GPIOs.
This board sets up THEJAS32 a test microcontroller, controlled by a Raspberry Pi Pico. Some of the IO interfaces are routed to the Pico. This opens the door for many types of experimentation and learning, including clock control, timing, peripheral emulation, etc.
Useful background and goals for this board are well covered in my recent talk at IndiaFOSS 2024 (video, 25 mins). There is also a AtiVEGA hackaday project page. Look at hackaday for updates, what's going on in the project, etc.
A somewhat detailed background and intro to the board is also in this presentation at ChennaiFOSS 2024 conference (video, 25 minutes) that I gave earlier this year.
This board is designed to be a low cost board, relying on off-the-shelf components as much as possible. The goal is to encourage easy assembly without advanced skills. For this reason, the smallest footprint chosen for passives is 0603.
Design
The board consists of a few main elements
- THEJAS32 SoC
- 2 MB flash (used by THEJAS32)
- Raspberry Pi Pico
- 2x Mini 360 DC-DC power modules - one to generate core voltage of 1.2V, other for 3.3V
The core of the board consists of
- THEJAS32 SoC
- 2 MB flash
The power and boot cycle of the THEJAS32 ("MCU") is primarily controlled using a few pins
- active low RESET can be pulled up by Master Pico to get it out of reset
- System clock is generated from a GPOUT capable pin of the Pico. System clock can thus be generated in many ways
- BOOT_SEL pin is controlled by Pico, allowing boot from SPI flash or UART.
- BOOT UART (UART0) is routed to Pico, enabling log capture and programming
Pins and interfaces are broken out into standard 0.1" headers. Dual row headers are mostly employed. When shorted, the interface gets routed from the MCU to the RP2040. This enables advanced experimentation, precise timing, peripheral emulation, co-processing, etc.
Board may be powered using the dedicated micro USB connector(J2) or through the Pico. Jumpers JP3 and JP4 decide the source of power. Both jumpers may also be populated, allowing the Pico to function as a USB host, but care must be taken not to connect Pico as a USB device in such cases. Refer to the schematic for more info.
Precise measurement of power draw of the THEJAS32 is also a goal of this board. Jumpers JP2 and JP1 are included for this purpose.
THEJAS32 IO
All IOs from THEJAS32 are broken out. Software can thus use all the pins. Some details are below; do refer the schematics for complete details.
UART
Boot UART is available on J3. This can be sent to the Pico for control, by using two jumpers.
J11 breaks out UART1 from THEJAS32.
Raspberry Pi HAT compatibility
Many Raspberry Pi HATs should be usable with this board, mounted on J12. THEJAS32 does not have any pin multiplexing. The most commonly used functions on the various pins are thus directly assigned, including I2C, SPI, UART and PWM and GPIOs. Refer the schematics for details.
A full size HAT can be mounted on this board. Additional through holes are provided to ensure mechanical support.
GPIO Breakout
J10 features 14 GPIOs - GPIO17 to GPIO30. States for these can be set one shot, by bit masking.
I2C and SPI
J4 breaks out I2C1 and SPI0.
J13 provides access to I2C0. This is also connected to the Pico, for control. Pico can be setup as an I2C slave and respond to I2C transfers initiated by THEJAS32.
Similarly SPI1 is available on J9, also connected to SPI interface on Pico. Pico can be setup as a SPI slave, and respong to transfers initiated by THEJAS32.
JTAG
J5 breaks out JTAG pins from THEJAS32. Fun fact: none of the official ARIES boards break out JTAG.
PWM
PWM pins 4,5,6 are broken out on J7. R32, R33 and R34 can be used to control the current.
Raspberry Pi Pico
Pico controls the runtime lifecycle of the THEJAS32, via the RESET and CLK pins. BOOT_SEL is also under Pico's control. Note that the Pico is an integral part of the board design, as it provides the clock signal to THEJAS32.
J8 and J6 can be used to interface external electronics directly to Pico. J8 has the debug UART.
A single ADC pin, clock pin (GPIO22) are available as well.
Tools
Based on KiCAD 8.
Checkout Instructions
This project uses git submodules. To checkout everything, do:
git clone --recurse-submodules https://github.com/shreekumar3d/thejas32-testbed.git
Raspberry Pi Pico footprint is a submodule. If you don't go this, you'll not see the nice Pico in the 3D preview.
shreekumar3d