The UDOO BOLT embeds a Microchip ATmega32u4 microcontroller, the same as Arduino® Leonardo, with the same open-source schematic.
The main AMD Ryzen™ processor and the ATmega32u4 microcontroller are connected through an internal USB serial connection, so it’s exactly like having an Arduino® Leonardo connected with a standard PC but all in a small form factor Single Board Computer.
The ATmega32u4 microcontroller is a low-power Microchip 8-bit AVR RISC-based microcontroller featuring 32KB self-programming flash program memory, 2.5KB SRAM, 1KB EEPROM, USB 2.0 full-speed/low speed device, 12-channel 10-bit A/D-converter, and JTAG interface for on-chip-debug. The device achieves up to 16 MIPS throughput at 16 MHz. 2.7 - 5.5 Volt operation.
More technical information about ATmega32u4, like the datasheet, can be found in the Microchip ATmega32u4 page.
From the Arduino Leonardo page:
"The Arduino Leonardo is a microcontroller board based on the ATmega32u4 (datasheet). It has 20 digital input/output pins (of which 7 can be used as PWM outputs and 12 as analog inputs), a 16 MHz crystal oscillator, a micro USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started.
The Leonardo differs from all preceding boards in that the ATmega32u4 has built-in USB communication, eliminating the need for a secondary processor. This allows the Leonardo to appear to a connected computer as a mouse and keyboard, in addition to a virtual (CDC) serial / COM port. It also has other implications for the behavior of the board; these are detailed on the getting started page."