Episode Details

For this week's EYE ON NPI, we'll Hazard a guess that you'll be excited to see the Raspberry Pi RP2350 chip available for purchase at Digi-Key for integration into your next design. We've been working with this chip for a few months and it's quickly becoming our favorite Arm Cortex chip, with fun peripherals and a well-supported toolchain. It also is one of the first mass-produced RISC-V chips: one that you can buy and start using for trying out RISC-V development without the 'risc' of worrying you may have picked the wrong core. Available in two chip sizes and with a boost in performance and peripherals, the RP2350 (https://www.digikey.com/short/mzpjhptm) represents a big upgrade to the RP2040 (https://www.digikey.com/en/products/detail/raspberry-pi/SC0914-13/14306010) that you've seen take over the microcontroller world over the last 4 years. Raspberry Pi is famous for their single board computers (https://www.digikey.com/en/products/filter/single-board-computers-sbcs/933) so much so that they created a full market for sub-$100 all-in-one PCs. The big disruption we feel they brought to the market was the creation of a hackable and open-source ecosystem with good main-line OS and driver support. With well-written documentation and up-to-date Linux software, purchasing a Pi meant you got to join in with a community that was having fun, not struggling with compiling out-of-tree kernel modules and closed-source firmware. So in 2021 when they announced the RP2040, folks were interested: could a SBC maker design low power silicon? Turns out, yes! The RP2040 was a fun dual-core 133 MHz Cortex-M0+ processor, with 264K of SRAM, with a satisfying collection of peripherals: USB, ADC, UART/SPI/I2C, PWM, DMA and timers plus the nifty PIO state machine (https://www.raspberrypi.com/news/what-is-pio/). The killer feature, though, was the price: at $1 a chip, and tons of availability with an on-going chip shortage, the RP2040 won our hearts and soldering stations! Three years later, Raspberry Pi is back with a sequel: The RP2350A (https://www.digikey.com/en/products/filter/microcontrollers/685?s=N4IgTCBcDaIE4AcwGYCsAGAgiAugXyA) and RP2350B (https://www.digikey.com/en/products/filter/microcontrollers/685?s=N4IgTCBcDaIE4AcwGYCsAGAQiAugXyA) two variants of an upgrade chip that keeps what was great about the '2040 but with some boosts. First up, the core was upgraded from dual Cortex-M0's to the M33: this means you get an FPU and better low-power performance, plus TrustZone security. The core is spec'd for 150MHz but we've overclocked it to 264MHz without too much complaint. You also have the option to get dual RISC-V cores (https://riscv.org/) instead. SRAM was also bumped: from 264K to 520KB. This is great for running interpreted languages like MicroPython (https://micropython.org/) or CircuitPython (https://circuitpython.org/). Like the original, the RP2350 does not have any built in FLASH memory. Instead, you will need to wire it to a QSPI flash memory chip (https://www.digikey.com/short/80t4zt5t). This way you can pick from 1 MBytes to 16 MBytes whatever your code size needs. This new chip adds the ability to wire in PSRAM (https://www.digikey.com/short/d8033bfw) to the same QSPI bus plus an extra chip select. This is not going to be nearly as fast as on-chip SRAM, but it's great when you want large working memory that the chip will manage for you: by configuring it in the CMakefile, you 'magically' get a huge area you can malloc. Another improvement is in the number of PIO blocks: the original had 2, the RP2350 has 3. The two biggest new features we found are the new HSTX peripheral and the 80-QFN RP2350B (https://www.digikey.com/en/products/filter/microcontrollers/685?s=N4IgTCBcDaIE4AcwGYCsAGAQiAugXyA) variant. HSTX stands for High Speed Transmission and its a high-speed peripheral that can drive 8 output lines - note that it's output only! There's a few possible use cases, but the core reasoning is that this lets you control a DVI displ