I've had a lot of fun messing with SiLabs EFM8 series chips recently. They've taken an 8051-compatible core and added a bunch of the peripherals you'd expect to

I've had a lot of fun messing with SiLabs EFM8 series chips recently. They've taken an 8051-compatible core and added a bunch of the peripherals you'd expect to find on a modern ARM SoC; SPI, I2C, USB, CAN, Watchdog, and the PWM/PCA module has a lot of interesting options for generating different waveforms. SiLabs provide a free license for Keil 8051, which is based on an absurdly old DOS assembler called A51.EXE (The Mac/Linux version runs under Wine behind the scenes). The SDCC toolchain supports 8051 fairly well, using code ported from the ASxxxxx project that dates back to the PDP-11 days! http://shop-pdp.net/ashtml/asmlnk.htm http://shop-pdp.net/ashtml/asmlnk.htm There was an attempt to add 8051 support to binutils and gdb in 2001, but the patches were never merged. If somebody's looking for a project to get their hands dirty... This would be a good one. https://sourceware.org/ml/binutils/2001-12/msg00489.html https://sourceware.org/ml/binutils/2001-12/msg00489.html https://sourceware.org/ml/binutils/2001-12/msg00488.html https://sourceware.org/ml/binutils/2001-12/msg00488.html I really like the 8051 ISA, it's simple enough to wrap your head around and the modern variants are competitive on price and power efficiency with things like the PIC and AVR. That said, with ARM Cortex-M0 chips costing only a few cents more and having active support in every toolchain, it's hard to argue for 8-bit solutions beyond nostalgia or sunk cost. Still, they're fun chips.