ESP32 ULP coprocessor instruction set

This document provides details about the instructions used by ESP32 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 register 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 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
uint32_t rtc_8md256_period = rtc_clk_cal(RTC_CAL_8MD256, 100);
uint32_t rtc_fast_freq_hz = 1000000ULL * (1 << RTC_CLK_CAL_FRACT) * 256 / rtc_8md256_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.

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

ST – Store data to the memory

Syntax

ST Rsrc, Rdst, offset

Operands

• Rsrc – Register R[0..3], holds the 16-bit value to store

• Rdst – Register R[0..3], address of the destination, in 32-bit words

• Offset – 13-bit signed value, offset in bytes

Cycles

4 cycles to execute, 4 cycles to fetch next instruction

Description

The instruction stores the 16-bit value of Rsrc to the lower half-word of memory with address Rdst+offset. The upper half-word is written with the current program counter (PC) (expressed in words, shifted left by 5 bits) OR’d with Rdst (0..3):

Mem[Rdst + offset / 4]{31:0} = {PC[10:0], 3'b0, Rdst, Rsrc[15:0]}

The application can use higher 16 bits to determine which instruction in the ULP program has written any particular word into memory.

Examples:

1:        ST  R1, R2, 0x12        //MEM[R2+0x12] = R1

2:        .data                   //Data section definition
  Addr1:  .word     123           // Define label Addr1 16 bit
          .set      offs, 0x00    // Define constant offs
          .text                   //Text section definition
          MOVE      R1, 1         // R1 = 1
          MOVE      R2, Addr1     // R2 = Addr1
          ST        R1, R2, offs  // MEM[R2 +  0] = R1
                                  // MEM[Addr1 + 0] will be 32'h600001

LD – Load data from the memory

Syntax

LD Rdst, Rsrc, offset

Operands

Rdst – Register R[0..3], destination

Rsrc – Register R[0..3], holds address of destination, in 32-bit words

Offset – 13-bit signed value, offset in bytes

Cycles

4 cycles to execute, 4 cycles to fetch next instruction

Description

The instruction loads lower 16-bit half-word from memory with address Rsrc+offset into the destination register Rdst:

Rdst[15:0] = Mem[Rsrc + offset / 4][15:0]

Examples:

1:        LD  R1, R2, 0x12            //R1 = MEM[R2+0x12]

2:        .data                       //Data section definition
  Addr1:  .word     123               // Define label Addr1 16 bit
          .set      offs, 0x00        // Define constant offs
          .text                       //Text section definition
          MOVE      R1, 1             // R1 = 1
          MOVE      R2, Addr1         // R2 = Addr1 / 4 (address of label is converted into words)
          LD        R1, R2, offs      // R1 = MEM[R2 +  0]
                                      // R1 will be 123

JUMP – Jump to an absolute address

Syntax

JUMP Rdst

JUMP ImmAddr

JUMP Rdst, Condition

JUMP ImmAddr, Condition

Operands

• Rdst – Register R[0..3] containing address to jump to (expressed in 32-bit words)

• ImmAddr – 13 bits address (expressed in bytes), aligned to 4 bytes

• Condition:

  • EQ – jump if last ALU operation result was zero

  • OV – jump if last ALU has set overflow flag

Cycles

2 cycles to execute, 2 cycles to fetch next instruction

Description

The instruction makes jump to the specified address. Jump can be either unconditional or based on an ALU flag.

Examples:

1:        JUMP       R1            // Jump to address in R1 (address in R1 is in 32-bit words)

2:        JUMP       0x120, EQ     // Jump to address 0x120 (in bytes) if ALU result is zero

3:        JUMP       label         // Jump to label
          ...
  label:  nop                      // Definition of label

4:        .global    label         // Declaration of global label

          MOVE       R1, label     // R1 = label (value loaded into R1 is in words)
          JUMP       R1            // Jump to label
          ...
  label:  nop                      // Definition of label

JUMPR – Jump to a relative offset (condition based on R0)

Syntax

JUMPR Step, Threshold, Condition

Operands

• 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 LT, GE, LE and GT: 2 cycles to execute, 2 cycles to fetch next instruction

Conditions LE and GT are implemented in the assembler using one JUMPR instructions:

// JUMPR target, threshold, GT is implemented as:

         JUMPR target, threshold+1, GE

// JUMPR target, threshold, LE is implemented as:

         JUMPR target, threshold + 1, LT

Conditions EQ is implemented in the assembler using two JUMPR instructions:

// JUMPR target, threshold, EQ is implemented as:

         JUMPR next, threshold + 1, GE
         JUMPR 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 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)

Syntax

JUMPS Step, Threshold, Condition

Operands

• 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

Conditions LE, LT, GE: 2 cycles to execute, 2 cycles to fetch next instruction

Conditions EQ, GT are implemented in the assembler using two JUMPS instructions:

// 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 example
          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
          READ_RTC_FIELD(RTC_CNTL_LOW_POWER_ST_REG, RTC_CNTL_RDY_FOR_WAKEUP)
          AND r0, r0, 1
          JUMP is_rdy_for_wakeup, eq    // Retry until the bit is set
          WAKE                          // Trigger wake up
          REG_WR 0x006, 24, 24, 0       // Stop ULP timer (clear RTC_CNTL_ULP_CP_SLP_TIMER_EN)
          HALT                          // Stop the ULP program
          // After these instructions, SoC will wake up,
          // and ULP will not run again until started by the main program.

SLEEP – set ULP wakeup timer period

Syntax

SLEEP sleep_reg

Operands

• sleep_reg – 0..4, selects one of SENS_ULP_CP_SLEEP_CYCx_REG registers.

Cycles

2 cycles to execute, 4 cycles to fetch next instruction

Description

The instruction selects which of the SENS_ULP_CP_SLEEP_CYCx_REG (x = 0..4) register values is to be used by the ULP wakeup timer as wakeup period. By default, the value from SENS_ULP_CP_SLEEP_CYC0_REG is used.

Examples:

1:        SLEEP     1         // Use period set in SENS_ULP_CP_SLEEP_CYC1_REG

2:        .set sleep_reg, 4   // Set constant
          SLEEP  sleep_reg    // Use period set in SENS_ULP_CP_SLEEP_CYC4_REG

WAIT – wait some number of cycles

Syntax

WAIT Cycles

Operands

• Cycles – number of cycles for wait

Cycles

2 + Cycles cycles to execute, 4 cycles to fetch next instruction

Description

The instruction delays for given number of cycles.

Examples:

1:        WAIT     10         // Do nothing for 10 cycles

2:        .set  wait_cnt, 10  // Set a constant
          WAIT  wait_cnt      // wait for 10 cycles

TSENS – do measurement with temperature sensor

Syntax

• TSENS Rdst, Wait_Delay

Operands

• Rdst – Destination Register R[0..3], result will be stored to this register

• Wait_Delay – number of cycles used to perform the measurement

Cycles

2 + Wait_Delay + 3 * TSENS_CLK to execute, 4 cycles to fetch next instruction

Description

The instruction performs measurement using TSENS and stores the result into a general purpose register.

Examples:

1:        TSENS     R1, 1000     // Measure temperature sensor for 1000 cycles,
                                 // and store result to R1

ADC – do measurement with ADC

Syntax

• ADC Rdst, Sar_sel, Mux

• ADC Rdst, Sar_sel, Mux, 0 — deprecated form

Operands

• Rdst – Destination Register R[0..3], result will be stored to this register

• Sar_sel – Select ADC: 0 = SARADC1, 1 = SARADC2

• Mux - Enable ADC channel. Channel number is [Mux-1]. If the user passes Mux value 1, then ADC channel 0 gets used.

Cycles

23 + max(1, SAR_AMP_WAIT1) + max(1, SAR_AMP_WAIT2) + max(1, SAR_AMP_WAIT3) + SARx_SAMPLE_CYCLE + SARx_SAMPLE_BIT cycles to execute, 4 cycles to fetch next instruction

Description

The instruction makes measurements from ADC.

Examples:

1:        ADC      R1, 0, 1      // Measure value using ADC1 channel 0 and store result into R1

I2C_RD - read single byte from I2C slave

Syntax

• I2C_RD Sub_addr, High, Low, Slave_sel

Operands

• Sub_addr – Address within the I2C slave to read.

• High, Low — Define range of bits to read. Bits outside of [High, Low] range are masked.

• Slave_sel - Index of I2C slave address to use.

Cycles

Execution time mostly depends on I2C communication time. 4 cycles to fetch next instruction.

Description

I2C_RD instruction reads one byte from I2C slave with index Slave_sel. Slave address (in 7-bit format) has to be set in advance into SENS_I2C_SLAVE_ADDRx register field, where x == Slave_sel. 8 bits of read result is stored into R0 register.

Examples:

1:        I2C_RD      0x10, 7, 0, 0      // Read byte from sub-address 0x10 of slave with address set in SENS_I2C_SLAVE_ADDR0

I2C_WR - write single byte to I2C slave

Syntax

• I2C_WR Sub_addr, Value, High, Low, Slave_sel

Operands

• Sub_addr – Address within the I2C slave to write.

• Value – 8-bit value to be written.

• High, Low — Define range of bits to write. Bits outside of [High, Low] range are masked.

• Slave_sel - Index of I2C slave address to use.

Cycles

Execution time mostly depends on I2C communication time. 4 cycles to fetch next instruction.

Description

I2C_WR instruction writes one byte to I2C slave with index Slave_sel. Slave address (in 7-bit format) has to be set in advance into SENS_I2C_SLAVE_ADDRx register field, where x == Slave_sel.

Examples:

1:        I2C_WR      0x20, 0x33, 7, 0, 1      // Write byte 0x33 to sub-address 0x20 of slave with address set in SENS_I2C_SLAVE_ADDR1.

REG_RD – read from peripheral register

Syntax

REG_RD Addr, High, Low

Operands

• Addr – Register address, in 32-bit words

• High – Register end bit number

• Low – Register start bit number

Cycles

4 cycles to execute, 4 cycles to fetch next instruction

Description

The instruction reads up to 16 bits from a peripheral register into a general purpose register: R0 = REG[Addr][High:Low].

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 DPORT bus as follows:

addr_ulp = (addr_dport - DR_REG_RTCCNTL_BASE) / 4

Examples:

1:        REG_RD      0x120, 7, 4     // load 4 bits: R0 = {12'b0, REG[0x120][7:4]}

REG_WR – write to peripheral register

Syntax

REG_WR Addr, High, Low, Data

Operands

• Addr – Register address, in 32-bit words.

• High – Register end bit number

• Low – Register start bit number

• Data – Value to write, 8 bits

Cycles

8 cycles to execute, 4 cycles to fetch next instruction

Description

The instruction writes up to 8 bits from an immediate data value into a peripheral register: REG[Addr][High:Low] = data.

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 DPORT bus as follows:

addr_ulp = (addr_dport - DR_REG_RTCCNTL_BASE) / 4

Examples:

1:        REG_WR      0x120, 7, 0, 0x10   // set 8 bits: REG[0x120][7:0] = 0x10

Convenience macros for peripheral registers access

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 */
READ_RTC_FIELD(SENS_SAR_SLAVE_ADDR3_REG, SENS_TSENS_OUT)

WRITE_RTC_REG(rtc_reg, low_bit, bit_width, value)

Write immediate value into rtc_reg[low_bit + bit_width - 1 : low_bit], bit_width <= 8. For example:

#include "soc/soc_ulp.h"
#include "soc/rtc_io_reg.h"

/* Set BIT(2) of RTC_GPIO_OUT_DATA_W1TS field in RTC_GPIO_OUT_W1TS_REG */
WRITE_RTC_REG(RTC_GPIO_OUT_W1TS_REG, RTC_GPIO_OUT_DATA_W1TS_S + 2, 1, 1)

WRITE_RTC_FIELD(rtc_reg, field, value)

Write immediate value into a field in rtc_reg, up to 8 bits. For example:

#include "soc/soc_ulp.h"
#include "soc/rtc_cntl_reg.h"

/* Set RTC_CNTL_ULP_CP_SLP_TIMER_EN field of RTC_CNTL_STATE0_REG to 0 */
WRITE_RTC_FIELD(RTC_CNTL_STATE0_REG, RTC_CNTL_ULP_CP_SLP_TIMER_EN, 0)

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