CH32V003 tidbits

A minimalistic prototyping PCB can be made with a 0.1uF soldered onto pin 7 and 9 of a TSSOP-20 breakout board. The back side of the PCB contains SOIC pads that can be used for the 8 and 16 pins versions of the chip.  The chip can operate between 2.7V to 5V with the reset threshold programmable from 2.7V to 4.4V.

Minimalistic CH32V003 prototyping board

Core

QingKe V2 series microprocessor is a 32-bit general-purpose MCU microprocessor based on the standard 
RISC-V instruction subset RV32E(Base Integer Instruction Set) C(16-bit compression instruction) with only 16 general-purpose registers.

V2 series supports addition to custom XW extensions, Hardware Prologue/Epilogue (HPE), Vector Table Free (VTF), single-wire serial debug interface (SDI), and support for "WFE" instructions.

The following topics are covered in their QingKeV2_Processor_Manual 

Chapter 2 Exception 

Chapter 3 PFIC and Interrupt Control 

Chapter 4 System Timer (SysTick)

Chapter 5 Processor Low-power Settings 

Chapter 7 CSR Register List 

See reference manual for peripheral programming and application code example. The debug protocol and debug registers are documented in the RISC-V QingKeV2 Microprocessor Debug Manual.

GPIO

While CH32V003F4 pins are backward compatible with STM8F3 (TSSOP-20), 2 additional GPIO pins are available - VCAP pin is replaced as PD0 and NRST as PD7 (selectable via User Option Bytes) .

There are some GPIO input threshold differences between the STM8 and CH32V003.

I/O characteristics: STM8 has CMOS input threshold while CH32v003 has LVTTL threshold.

Note: Pull down resistors I normally use for push buttons on shared I/O needs to be below 8.9K.

3.3V * 8.9K /(8.9K + 30K) = 0.755V and 5V * 8.9K/(8.9K + 30K) = 1.144V

There are four 5V tolerant pins: PC1, PC2, PC5, PC6 (vs 2 in STM8) and up to 8 ADC pins. The alternate functions are more flexible as some can be mapped to additional GPIO pins. For the 20 pins package, Port C and D are rearranged as two contiguous 8-bit ports which make life easier for interfacing to byte-wise devices.

CH32V003F4P6 (TSSOP-20) GPIO pinout and their alternate functions

Bootloader

The chip doesn't have a Boot pin to select Bootloader externally. Instead there is a Mode bit that can be set to either jump to user code or bootload upon Reset.  SystemReset_StartMode(uint32_t Mode) under   

/EXAM/SRC/Peripheral/src/ch32v00x_flash.c in the application code example.

PlatformIO forum talks about how to modify the bootloader: here

Debricking

From EEVblog: Topic: CH32V003 -J4 (SOP8) pins (UPDATE: how to brick your -J4) 

WCH-Link Utility menu - Full Chip Erase

Resources:

There is a bit-bang USB implementation available in beta - RV003USB  This implementation looks much cleaner than the STM8 VUSB project that I have been using.  The USB pins are configurable in usb_config.h 

There is a CH32V003 F4P6 V-USB Development Board with the USB pins on PA1 and PA2.

Alternate IDE:

Visual Studio Code using Platform IO plugin and Community-PIO-CH32V platform

Upgrade path

The next cheapest upgrade is the CH32X035 or CH32X033 marketed as USB Connectivity parts.  They aren't pin compatible, but they can operate at 5V with the improved RISC-V core, FLASH, SRAM, ADC, UART, USB.

CH32X033/035 features

RV32I – Base Integer Instruction Set, 32-bit. Currently version 2.1
M – Standard Extension for Integer Multiplication and Division
A – Standard Extension for Atomic Instructions
C – Standard Extension for Compressed Instructions

The most accessible parts are the X033F8P6 and X035F7P6 TSSOP20 parts with cheaply available breakout boards.  I have originally ordered the TSSOP and find myself maxing out the GPIO very quickly for a couple of projects I have in mind.  I have ordered some QSOP28 but cannot find a cheap source for breakout boards. QSOP has a pin pitch of 0.635mm (0.025") which is slightly tighter than the 0.65mm pitch for TSSOP20 which I can manage with my home made PCB. Their 0.4mm pitched QFN parts on the other hand would require commercial quality PCB.

The USB bootloader is activated by pulling up on the USB D+ pin at power on.