Has RISC-V finally made the 8051 obsolete?

8051 (MCS-51)

You can probably tell from the tone of the title that I'm no fan of the 8051. The 8051 is an 8-bit MCU created by Intel in 1980. It has a very simple (aka wimpy) instruction set that was designed to minimize the amount of silicon required. This and the fact that the IP of the 8051 was released as free to the public, made it a popular choice as the CPU core of MCUs from a variety of vendors. Taken from a purely hardware point of view, the 8051 seems like a great way to make low cost MCUs, but from a software developers POV (e.g. mine), it's a productivity killing choice. The reasons I feel this way are:

  • The HW architecture has so many odd quirks and limitations that your code ends up being a specialized mess that has no hope of portability to any other architecture
  • 8-bit ops mean that your code becomes very bulky to do actual work besides blinking some LEDs
  • What you save in HW cost, you pay dearly for in SW cost
  • The available SW tools are very limited (e.g. SDCC - C compiler, 8051 assembler)
  • The lack of stack/RAM space means that imaging, wireless protocols and anything remotely complicated, when written for the 8051, will be a complicated mess

Besides all of these negatives, it continues to be used in modern designs because it helps reduce the cost of the final product.

Cannibalizing Your Products

Any large company which continuously develops long-lived, diversified products will eventually cannibalize their own in order to innovate. It appears that WCH is now doing so with their RISC-V MCUs overtaking their 8051 MCUs and even selling them at a lower cost. For the last few weeks, I've been creating various PCBs for their new CH32X03x line of MCUs (33/34/35). This is a series of low cost RISC-V MCUs that feature native USBFS (device+host) and USBPD support. They're an order of magnitude more powerful than the CH5xx series and cost less! Price and availability of this new series has been a bit uneven, but judging by the cost from the same marketplace (e.g. AliExpress), the CH32X series will remain lower cost compared to the CH5xx series. Here's a quick list of the differences:

CH32X035
48Mhz 32-bit RISC-V
20K SRAM
62K FLASH + 3K bootloader
USBFS + USBPD
Vcc 2.7 to 5.5V
ADC w/capacitive touch support
The usual assortment of UART/I2C/SPI/GPIO/Timers

CH559 (the most powerful one)
56Mhz 8-bit 8051
6.25K SRAM
63K FLASH
USBFS
Vcc 3.3 to 5V
The usual assortment of UART/I2C/SPI/GPIO/ADC/Timers

The CH559 currently costs about twice as much as the CH32X for a similar package (number of exposed pins).

Through the features and pricing, it certainly appears that WCH wants you to use the CH32X instead of the CH5xx. A similar story can be seen with the ubiquitous CH340 series. A CH32X can do the same job (USB-CDC to UART) at lower cost. The CH32V203 is priced about the same as the CH559, yet is even more powerful than the CH32X035.

I've been experimenting with the CH32X033 (purchased on AliExpress for 23 cents each) and have been impressed with how well it works. One thing to note is that the first batch of shipping chips has a defect in a few of the I/O lines of GPIO port A which prevents hardware I2C from working. The GPIO lines are usable for output and input, but the internal pull-up and pull-down resistors don't work. Hopefully this is resolved in the next batch.

I'll update this with new info if a newer batch fixes the problem...


Comments

Post a Comment

Popular posts from this blog

Surprise! ESP32-S3 has (a few) SIMD instructions

Intro Espressif Systems released their ESP32-S3 SoC a few years ago, but only recently have they released more documentation and support of its full capabilities. Without any changes to your code, the S3 runs about 15% faster than older ESP32 CPUs at the same clock speed. It has a 'hidden' capability that's more difficult to use, but can be worth the effort if you need more speed. This article is aimed at programmers who are already familiar with SIMD instructions on other platforms. I've been optimizing code with SIMD for more than 15 years on Intel, Arm and DSPs (even Cadence's), so when I heard that the S3 had SIMD instructions, I immediately went searching for documentation. When the S3 became available to buy, there was only a promise of documentation and support. In the 2+ years since then, not much has changed. At the end of 2023, Espressif released a document describing the new instructions: S3 Technical Reference Manual The document has a decent level of d...
Read more

How much current do OLED displays use?

Image
Those little OLED displays are everywhere, and there's a good reason. They're inexpensive, easy to program and they look good. I wanted to explore how much current they draw so that I can plan better for battery powered projects. Questions I want answered: How much idle current is drawn when the controller is off versus on (blank display)? What's the minimum current to see text indoors? What's the maximum current when all pixels are on at their brightest? How does display size affect current draw? How does active data writing affect current draw? It's obvious they use more, but how much current do grayscale and color OLEDs use? How practical are OLED displays compared to common LCDs for battery powered projects? Materials: Cheap multimeter (manual scale, assumed accuracy +/-10% at worst) Various OLED displays (72x40, 96x16, 128x32, 64x32, 128x64-0.96", 128x64-1.3") Arduino compatible microcontroller ( Adafruit nRF52840 Feather Express ) ...
Read more

Fast SSD1306 OLED drawing with I2C bit banging

Image
What The  SSD1306  OLED displays are very popular with hobbyists due to their low cost and easy interfacing. The majority of the ones sold expose a two wire interface (TWI) aka I2C. The default speed for I2C is 100Khz and the "fast" mode is 400Khz. These are the 2 standard speeds supported by most AVR Arduinos. An I2C clock rate of around 800Khz is also possible on AVR MCUs, but not supported directly by the Wire library. The I2C standard recently added some higher speeds (1Mhz and 3.4Mhz). The 3.4Mhz version uses a slightly different protocol. At 400Khz, using the I2C hardware and the Wire library, I was able to refresh the display around 23.5 frames per second (FPS) with my code. Why I have already written a SSD1306  library for both Linux and Arduino, but I wanted to drive the display from an ATtiny85 and learn about the I2C protocol in the process. The ATtiny85 doesn't have I2C hardware built in, so it needs to be emulated in software using GPIO pins. There ...
Read more