This document provides details about the instructions used by ESP32-S2 ULP coprocessor assembler.
ULP coprocessor has 4 16-bit general purpose registers, labeled R0, R1, R2, R3. It also has an 8-bit counter register (stage_cnt) which can be used to implement loops. Stage count regiter is accessed using special instructions.
ULP coprocessor can access 8k bytes of RTC_SLOW_MEM memory region. Memory is addressed in 32-bit word units. It can also access peripheral registers in RTC_CNTL, RTC_IO, and SENS peripherals.
All instructions are 32-bit. Jump instructions, ALU instructions, peripheral register and memory access instructions are executed in 1 cycle. Instructions which work with peripherals (TSENS, ADC, I2C) take variable number of cycles, depending on peripheral operation.
The instruction syntax is case insensitive. Upper and lower case letters can be used and intermixed arbitrarily. This is true both for register names and instruction names.
Note about addressing
---------------------
ESP32-S2 ULP coprocessor's JUMP, ST, LD instructions which take register as an argument (jump address, store/load base address) expect the argument to be expressed in 32-bit words.
Consider the following example program::
entry:
NOP
NOP
NOP
NOP
loop:
MOVE R1, loop
JUMP R1
When this program is assembled and linked, address of label ``loop`` will be equal to 16 (expressed in bytes). However `JUMP` instruction expects the address stored in register to be expressed in 32-bit words. To account for this common use case, assembler will convert the address of label `loop` from bytes to words, when generating ``MOVE`` instruction, so the code generated code will be equivalent to::
0000 NOP
0004 NOP
0008 NOP
000c NOP
0010 MOVE R1, 4
0014 JUMP R1
The other case is when the argument of ``MOVE`` instruction is not a label but a constant. In this case assembler will use the value as is, without any conversion::
.set val, 0x10
MOVE R1, val
In this case, value loaded into R1 will be ``0x10``.
Similar considerations apply to ``LD`` and ``ST`` instructions. Consider the following code::
.global array
array: .long 0
.long 0
.long 0
.long 0
MOVE R1, array
MOVE R2, 0x1234
ST R2, R1, 0 // write value of R2 into the first array element,
// i.e. array[0]
ST R2, R1, 4 // write value of R2 into the second array element
// (4 byte offset), i.e. array[1]
ADD R1, R1, 2 // this increments address by 2 words (8 bytes)
ST R2, R1, 0 // write value of R2 into the third array element,
// i.e. array[2]
Note about instruction execution time
-------------------------------------
ULP coprocessor is clocked from RTC_FAST_CLK, which is normally derived from the internal 8MHz oscillator. Applications which need to know exact ULP clock frequency can calibrate it against the main XTAL clock::
#include "soc/rtc.h"
// calibrate 8M/256 clock against XTAL, get 8M/256 clock period
ULP coprocessor needs certain number of clock cycles to fetch each instruction, plus certain number of cycles to execute it, depending on the instruction. See description of each instruction below for details on the execution time.
Instruction fetch time is:
- 2 clock cycles — for instructions following ALU and branch instructions.
- 4 clock cycles — in other cases.
Note that when accessing RTC memories and RTC registers, ULP coprocessor has lower priority than the main CPUs. This means that ULP coprocessor execution may be suspended while the main CPUs access same memory region as the ULP.
Difference between ESP32 ULP and ESP32-S2 ULP Instruction sets
Compare to the ESP32 ULP coprocessor, the ESP-S2 ULP coprocessor has extended instruction set. The ESP32-S2 ULP is not binary compatible with ESP32 ULP,
but the assembled program that was written for the ESP32 ULP will also work on the ESP32-S2 ULP after rebuild.
The list of the new instructions that was added to the ESP32-S2 ULP is: LDL, LDH, STO, ST32, STI32.
The detailed description of these commands please see below.
**NOP** - no operation
----------------------
**Syntax**
**NOP**
**Operands**
None
**Cycles**
2 cycle to execute, 4 cycles to fetch next instruction
**Description**
No operation is performed. Only the PC is incremented.
**Example**::
1: NOP
**ADD** - Add to register
-------------------------
**Syntax**
**ADD***Rdst, Rsrc1, Rsrc2*
**ADD***Rdst, Rsrc1, imm*
**Operands**
-*Rdst* - Register R[0..3]
-*Rsrc1* - Register R[0..3]
-*Rsrc2* - Register R[0..3]
-*Imm* - 16-bit signed value
**Cycles**
2 cycles to execute, 4 cycles to fetch next instruction
**Description**
The instruction adds source register to another source register or to a 16-bit signed value and stores result to the destination register.
**Examples**::
1: ADD R1, R2, R3 //R1 = R2 + R3
2: Add R1, R2, 0x1234 //R1 = R2 + 0x1234
3: .set value1, 0x03 //constant value1=0x03
Add R1, R2, value1 //R1 = R2 + value1
4: .global label //declaration of variable label
Add R1, R2, label //R1 = R2 + label
...
label: nop //definition of variable label
**SUB** - Subtract from register
--------------------------------
**Syntax**
**SUB***Rdst, Rsrc1, Rsrc2*
**SUB***Rdst, Rsrc1, imm*
**Operands**
-*Rdst* - Register R[0..3]
-*Rsrc1* - Register R[0..3]
-*Rsrc2* - Register R[0..3]
-*Imm* - 16-bit signed value
**Cycles**
2 cycles to execute, 4 cycles to fetch next instruction
**Description**
The instruction subtracts the source register from another source register or subtracts 16-bit signed value from a source register, and stores result to the destination register.
**Examples**::
1: SUB R1, R2, R3 //R1 = R2 - R3
2: sub R1, R2, 0x1234 //R1 = R2 - 0x1234
3: .set value1, 0x03 //constant value1=0x03
SUB R1, R2, value1 //R1 = R2 - value1
4: .global label //declaration of variable label
SUB R1, R2, label //R1 = R2 - label
....
label: nop //definition of variable label
**AND** - Logical AND of two operands
-------------------------------------
**Syntax**
**AND***Rdst, Rsrc1, Rsrc2*
**AND***Rdst, Rsrc1, imm*
**Operands**
-*Rdst* - Register R[0..3]
-*Rsrc1* - Register R[0..3]
-*Rsrc2* - Register R[0..3]
-*Imm* - 16-bit signed value
**Cycles**
2 cycles to execute, 4 cycles to fetch next instruction
**Description**
The instruction does logical AND of a source register and another source register or 16-bit signed value and stores result to the destination register.
**Examples**::
1: AND R1, R2, R3 //R1 = R2 & R3
2: AND R1, R2, 0x1234 //R1 = R2 & 0x1234
3: .set value1, 0x03 //constant value1=0x03
AND R1, R2, value1 //R1 = R2 & value1
4: .global label //declaration of variable label
AND R1, R2, label //R1 = R2 & label
...
label: nop //definition of variable label
**OR** - Logical OR of two operands
-----------------------------------
**Syntax**
**OR***Rdst, Rsrc1, Rsrc2*
**OR***Rdst, Rsrc1, imm*
**Operands**
-*Rdst* - Register R[0..3]
-*Rsrc1* - Register R[0..3]
-*Rsrc2* - Register R[0..3]
-*Imm* - 16-bit signed value
**Cycles**
2 cycles to execute, 4 cycles to fetch next instruction
**Description**
The instruction does logical OR of a source register and another source register or 16-bit signed value and stores result to the destination register.
**Examples**::
1: OR R1, R2, R3 //R1 = R2 \| R3
2: OR R1, R2, 0x1234 //R1 = R2 \| 0x1234
3: .set value1, 0x03 //constant value1=0x03
OR R1, R2, value1 //R1 = R2 \| value1
4: .global label //declaration of variable label
OR R1, R2, label //R1 = R2 \|label
...
label: nop //definition of variable label
**LSH** - Logical Shift Left
----------------------------
**Syntax**
**LSH***Rdst, Rsrc1, Rsrc2*
**LSH***Rdst, Rsrc1, imm*
**Operands**
-*Rdst* - Register R[0..3]
-*Rsrc1* - Register R[0..3]
-*Rsrc2* - Register R[0..3]
-*Imm* - 16-bit signed value
**Cycles**
2 cycles to execute, 4 cycles to fetch next instruction
**Description**
The instruction does logical shift to left of source register to number of bits from another source register or 16-bit signed value and store result to the destination register.
**Examples**::
1: LSH R1, R2, R3 //R1 = R2 << R3
2: LSH R1, R2, 0x03 //R1 = R2 << 0x03
3: .set value1, 0x03 //constant value1=0x03
LSH R1, R2, value1 //R1 = R2 << value1
4: .global label //declaration of variable label
LSH R1, R2, label //R1 = R2 << label
...
label: nop //definition of variable label
**RSH** - Logical Shift Right
-----------------------------
**Syntax**
**RSH***Rdst, Rsrc1, Rsrc2*
**RSH***Rdst, Rsrc1, imm*
**Operands**
*Rdst* - Register R[0..3]
*Rsrc1* - Register R[0..3]
*Rsrc2* - Register R[0..3]
*Imm* - 16-bit signed value
**Cycles**
2 cycles to execute, 4 cycles to fetch next instruction
**Description**
The instruction does logical shift to right of source register to number of bits from another source register or 16-bit signed value and store result to the destination register.
**Examples**::
1: RSH R1, R2, R3 //R1 = R2 >> R3
2: RSH R1, R2, 0x03 //R1 = R2 >> 0x03
3: .set value1, 0x03 //constant value1=0x03
RSH R1, R2, value1 //R1 = R2 >> value1
4: .global label //declaration of variable label
RSH R1, R2, label //R1 = R2 >> label
label: nop //definition of variable label
**MOVE**– Move to register
---------------------------
**Syntax**
**MOVE***Rdst, Rsrc*
**MOVE***Rdst, imm*
**Operands**
-*Rdst*– Register R[0..3]
-*Rsrc*– Register R[0..3]
-*Imm*– 16-bit signed value
**Cycles**
2 cycles to execute, 4 cycles to fetch next instruction
**Description**
The instruction move to destination register value from source register or 16-bit signed value.
Note that when a label is used as an immediate, the address of the label will be converted from bytes to words. This is because LD, ST, and JUMP instructions expect the address register value to be expressed in words rather than bytes. To avoid using an extra instruction
**Examples**::
1: MOVE R1, R2 //R1 = R2
2: MOVE R1, 0x03 //R1 = 0x03
3: .set value1, 0x03 //constant value1=0x03
MOVE R1, value1 //R1 = value1
4: .global label //declaration of label
MOVE R1, label //R1 = address_of(label) / 4
...
label: nop //definition of label
**STL**/**ST**– Store data to the low 16 bits of 32-bits memory
-*Step*– relative shift from current position, in bytes
-*Threshold*– threshold value for branch condition
-*Condition*:
-*EQ* (equal) – jump if value in R0 == threshold
-*LT* (less than) – jump if value in R0 < threshold
-*LE* (less or equal) – jump if value in R0 <= threshold
-*GT* (greater than) – jump if value in R0 > threshold
-*GE* (greater or equal) – jump if value in R0 >= threshold
**Cycles**
Conditions *EQ*, *GT* and *LT*: 2 cycles to execute, 2 cycles to fetch next instruction
Conditions *LE* and *GE* are implemented in the assembler using two **JUMPR** instructions::
// JUMPR target, threshold, LE is implemented as:
JUMPR target, threshold, EQ
JUMPR target, threshold, LT
// JUMPR target, threshold, GE is implemented as:
JUMPR target, threshold, EQ
JUMPR target, threshold, GT
Therefore the execution time will depend on the branches taken: either 2 cycles to execute + 2 cycles to fetch, or 4 cycles to execute + 4 cycles to fetch.
**Description**
The instruction makes a jump to a relative address if condition is true. Condition is the result of comparison of R0 register value and the threshold value.
**Examples**::
1:pos: JUMPR 16, 20, GE // Jump to address (position + 16 bytes) if value in R0 >= 20
2: // Down counting loop using R0 register
MOVE R0, 16 // load 16 into R0
label: SUB R0, R0, 1 // R0--
NOP // do something
JUMPR label, 1, GE // jump to label if R0 >= 1
**JUMPS**– Jump to a relative address (condition based on stage count)
-*Step*– relative shift from current position, in bytes
-*Threshold*– threshold value for branch condition
-*Condition*:
-*EQ* (equal) – jump if value in stage_cnt == threshold
-*LT* (less than) – jump if value in stage_cnt < threshold
-*LE* (less or equal) - jump if value in stage_cnt <= threshold
-*GT* (greater than) – jump if value in stage_cnt > threshold
-*GE* (greater or equal) — jump if value in stage_cnt >= threshold
**Cycles**
2 cycles to execute, 2 cycles to fetch next instruction::
// JUMPS target, threshold, EQ is implemented as:
JUMPS next, threshold, LT
JUMPS target, threshold, LE
next:
// JUMPS target, threshold, GT is implemented as:
JUMPS next, threshold, LE
JUMPS target, threshold, GE
next:
Therefore the execution time will depend on the branches taken: either 2 cycles to execute + 2 cycles to fetch, or 4 cycles to execute + 4 cycles to fetch.
**Description**
The instruction makes a jump to a relative address if condition is true. Condition is the result of comparison of count register value and threshold value.
**Examples**::
1:pos: JUMPS 16, 20, EQ // Jump to (position + 16 bytes) if stage_cnt == 20
2: // Up counting loop using stage count register
STAGE_RST // set stage_cnt to 0
label: STAGE_INC 1 // stage_cnt++
NOP // do something
JUMPS label, 16, LT // jump to label if stage_cnt < 16
**STAGE_RST**– Reset stage count register
------------------------------------------
**Syntax**
**STAGE_RST**
**Operands**
No operands
**Description**
The instruction sets the stage count register to 0
**Cycles**
2 cycles to execute, 4 cycles to fetch next instruction
**Examples**::
1: STAGE_RST // Reset stage count register
**STAGE_INC**– Increment stage count register
----------------------------------------------
**Syntax**
**STAGE_INC***Value*
**Operands**
-*Value*– 8 bits value
**Cycles**
2 cycles to execute, 4 cycles to fetch next instruction
**Description**
The instruction increments stage count register by given value.
**Examples**::
1: STAGE_INC 10 // stage_cnt += 10
2: // Up counting loop example:
STAGE_RST // set stage_cnt to 0
label: STAGE_INC 1 // stage_cnt++
NOP // do something
JUMPS label, 16, LT // jump to label if stage_cnt < 16
**STAGE_DEC**– Decrement stage count register
----------------------------------------------
**Syntax**
**STAGE_DEC***Value*
**Operands**
-*Value*– 8 bits value
**Cycles**
2 cycles to execute, 4 cycles to fetch next instruction
**Description**
The instruction decrements stage count register by given value.
**Examples**::
1: STAGE_DEC 10 // stage_cnt -= 10;
2: // Down counting loop exaple
STAGE_RST // set stage_cnt to 0
STAGE_INC 16 // increment stage_cnt to 16
label: STAGE_DEC 1 // stage_cnt--;
NOP // do something
JUMPS label, 0, GT // jump to label if stage_cnt > 0
**HALT**– End the program
--------------------------
**Syntax**
**HALT**
**Operands**
No operands
**Cycles**
2 cycles to execute
**Description**
The instruction halts the ULP coprocessor and restarts ULP wakeup timer, if it is enabled.
**Examples**::
1: HALT // Halt the coprocessor
**WAKE**– Wake up the chip
---------------------------
**Syntax**
**WAKE**
**Operands**
No operands
**Cycles**
2 cycles to execute, 4 cycles to fetch next instruction
**Description**
The instruction sends an interrupt from ULP to RTC controller.
- If the SoC is in deep sleep mode, and ULP wakeup is enabled, this causes the SoC to wake up.
- If the SoC is not in deep sleep mode, and ULP interrupt bit (RTC_CNTL_ULP_CP_INT_ENA) is set in RTC_CNTL_INT_ENA_REG register, RTC interrupt will be triggered.
Note that before using WAKE instruction, ULP program may needs to wait until RTC controller is ready to wake up the main CPU. This is indicated using RTC_CNTL_RDY_FOR_WAKEUP bit of RTC_CNTL_LOW_POWER_ST_REG register. If WAKE instruction is executed while RTC_CNTL_RDY_FOR_WAKEUP is zero, it has no effect (wake up does not occur).
**Examples**::
1: is_rdy_for_wakeup: // Read RTC_CNTL_RDY_FOR_WAKEUP bit
This instruction can access registers in RTC_CNTL, RTC_IO, SENS, and RTC_I2C peripherals. Address of the the register, as seen from the ULP, can be calculated from the address of the same register on the PeriBUS1 as follows::
This instruction can access registers in RTC_CNTL, RTC_IO, SENS, and RTC_I2C peripherals. Address of the the register, as seen from the ULP, can be calculated from the address of the same register on the PeriBUS1 as follows::
ULP source files are passed through C preprocessor before the assembler. This allows certain macros to be used to facilitate access to peripheral registers.
Some existing macros are defined in ``soc/soc_ulp.h`` header file. These macros allow access to the fields of peripheral registers by their names.
Peripheral registers names which can be used with these macros are the ones defined in ``soc/rtc_cntl_reg.h``, ``soc/rtc_io_reg.h``, ``soc/sens_reg.h``, and ``soc/rtc_i2c_reg.h``.
READ_RTC_REG(rtc_reg, low_bit, bit_width)
Read up to 16 bits from rtc_reg[low_bit + bit_width - 1 : low_bit] into R0. For example::
#include "soc/soc_ulp.h"
#include "soc/rtc_cntl_reg.h"
/* Read 16 lower bits of RTC_CNTL_TIME0_REG into R0 */
READ_RTC_REG(RTC_CNTL_TIME0_REG, 0, 16)
READ_RTC_FIELD(rtc_reg, field)
Read from a field in rtc_reg into R0, up to 16 bits. For example::
#include "soc/soc_ulp.h"
#include "soc/sens_reg.h"
/* Read 8-bit SENS_TSENS_OUT field of SENS_SAR_SLAVE_ADDR3_REG into R0 */
