Espressif ESP32 Technical Reference Manual page 666

30 ULP Coprocessor (ULP)
30.3 Functional Description
The ULP coprocessor is a programmable FSM (Finite State Machine) that can work during deep sleep. Like
general-purpose CPUs, ULP coprocessor also has some instructions which can be useful for a relatively
complex logic, and also some special commands for RTC controllers/peripherals. The 8 KB of SRAM RTC slow
memory can be accessed by both the ULP coprocessor and the CPU; hence, it is usually used to store
instructions and share data between the ULP coprocessor and the CPU.
The ULP coprocessor can be started by software or a periodically-triggered timer. The operation of the ULP
coprocessor is ended by executing the
RTC domain, either through built-in instructions or RTC registers. In many cases the ULP coprocessor can be a
good supplement to, or replacement of, the CPU, especially for power-sensitive applications. Figure
shows the overall layout of a ULP coprocessor.
30.4 Instruction Set
The ULP coprocessor provides the following instructions:
• Perform arithmetic and logic operations - ALU
• Load and store data - LD, ST, REG_RD and REG_WR
• Jump to a certain address - JUMP
• Manage program execution - WAIT/HALT
• Control sleep period of ULP coprocessor - SLEEP
• Wake up/communicate with SoC - WAKE
• Take measurements - ADC
• Communicate using I²C - I2C_RD/I2C_WR
The ULP coprocessor's instruction format is shown in Figure 30-2.
31 28 27
OpCode
An instruction, which has one OpCode, can perform various different operations, depending on the setting of
Operands bits. A good example is the
operations; or the JUMP
Each instruction has a fixed width of 32 bits. A series of instructions can make a program be executed by the
ULP coprocessor. The execution flow inside the program uses 32-bit addressing. The program is stored in a
dedicated region called Slow Memory (RTC_SLOW_MEM), which is visible to the main CPUs as one that has
an address range of 0x5000_0000 to 0x5000_1FFF (8 KB).
The OpCode in this chapter is represented by 4'dx, where 4 stands for 4-bit width, 'd is a decimal symbol,
stands for the value of OpCode (x: 0 ~ 15).
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HALT instruction. Meanwhile, it can access almost every module in
Figure 30-2. The ULP Coprocessor Instruction Format
ALU instruction, which is able to perform 10 arithmetic and logic
instruction, which may be conditional or unconditional, absolute or relative.
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Operands
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30-1
0
x
ESP32 TRM (Version 5.2)