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‎Makefile

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#
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# This is a project Makefile. It is assumed the directory this Makefile resides in is a
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# project subdirectory.
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#
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PROJECT_NAME := ulp-i2c
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include $(IDF_PATH)/make/project.mk
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‎README.md

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‎main/component.mk

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#
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# ULP support additions to component makefile.
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#
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# 1. ULP_APP_NAME must be unique (if multiple components use ULP)
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# Default value, override if necessary:
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ULP_APP_NAME ?= ulp_$(COMPONENT_NAME)
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#
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# 2. Specify all assembly source files here.
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# Files should be placed into a separate directory (in this case, ulp/),
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# which should not be added to COMPONENT_SRCDIRS.
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ULP_S_SOURCES = $(addprefix $(COMPONENT_PATH)/ulp/, \
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i2c.S \
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i2c-bmp180.S \
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)
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#
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# 3. List all the component object files which include automatically
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# generated ULP export file, $(ULP_APP_NAME).h:
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ULP_EXP_DEP_OBJECTS := ulp_example_main.o
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#
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# 4. Include build rules for ULP program
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include $(IDF_PATH)/components/ulp/component_ulp_common.mk
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#
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# Link object files and generate map file
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$(ULP_ELF): $(ULP_OBJECTS) $(ULP_LD_SCRIPT)
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$(summary) ULP_LD $(patsubst $(PWD)/%,%,$(CURDIR))/$@
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$(ULP_LD) -o $@ -A elf32-esp32ulp -Map=$(ULP_MAP) -T $(ULP_LD_SCRIPT) $(ULP_OBJECTS)
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#
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# End of ULP support additions to component makefile.
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#

‎main/ulp/i2c-bmp180.S

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/*
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* Demo of I2C ULP routines
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*/
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#include "soc/rtc_cntl_reg.h"
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#include "soc/rtc_io_reg.h"
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#include "soc/soc_ulp.h"
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#include "stack.S"
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.set BMP180_ADDR,0x77 // 7-bit address
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.set WRITE,((BMP180_ADDR << 1) | 0)
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.set READ,((BMP180_ADDR << 1) | 1)
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.set BMP180_REG_CONTROL,0xF4
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.set BMP180_REG_RESULT,0xF6
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.set BMP180_COMMAND_TEMPERATURE,0x2E
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.set BMP180_COMMAND_PRESSURE0,0x34
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.set BMP180_COMMAND_PRESSURE1,0x74
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.set BMP180_COMMAND_PRESSURE2,0xB4
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.set BMP180_COMMAND_PRESSURE3,0xF4
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.macro status s
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move r1,status
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move r0,\s
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st r0,r1,0
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.endm
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/* Define variables, which go into .bss section (zero-initialized data) */
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.bss
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.global status
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status: .long 0
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.global stack
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stack:
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.skip 100
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.global stackEnd
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stackEnd:
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.long 0
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/* Code goes into .text section */
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.text
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.global entry
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entry:
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move r3,stackEnd
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status 1
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wait 100
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psr
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jump i2c_start_cond
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move r2,WRITE
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psr
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jump i2c_write_byte
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jumpr fail,1,ge
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status 2
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move r2,BMP180_REG_CONTROL
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psr
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jump i2c_write_byte
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move r2,BMP180_COMMAND_TEMPERATURE
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psr
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jump i2c_write_byte
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psr
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jump i2c_stop_cond
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move r2,5
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psr
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jump waitMs
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psr
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jump i2c_start_cond
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move r2,WRITE
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psr
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jump i2c_write_byte
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move r2,BMP180_REG_RESULT
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psr
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jump i2c_write_byte
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psr
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jump i2c_start_cond
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move r2,READ
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psr
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jump i2c_write_byte
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move r2,0
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psr
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jump i2c_read_byte
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move r2,1 // last byte
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psr
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jump i2c_read_byte
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psr
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jump i2c_stop_cond
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wait 100
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fail:
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wake_up:
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/* Wake up the SoC, end program */
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wake
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halt
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waitMs:
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wait 8000
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sub r2,r2,1
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jump doneWaitMs,eq
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jump waitMs
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doneWaitMs:
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ret

‎main/ulp/i2c.S

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/*
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* Demo of I2C ULP routines
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*/
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#include "soc/rtc_cntl_reg.h"
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#include "soc/rtc_io_reg.h"
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#include "soc/soc_ulp.h"
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#include "stack.S"
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/*
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* =============================== I2C code ==========================================
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* Implementation of pseudo code from
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* https://en.wikipedia.org/wiki/I%C2%B2C#Example_of_bit-banging_the_I.C2.B2C_master_protocol
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*/
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.bss
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i2c_started:
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.long 0
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.text
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.global i2c_start_cond
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.global i2c_stop_cond
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.global i2c_write_bit
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.global i2c_read_bit
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.global i2c_write_byte
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.global i2c_read_byte
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.macro I2C_delay
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wait 38 // minimal 4.7us
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.endm
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.macro read_SCL // Return current level of SCL line, 0 or 1
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READ_RTC_REG(RTC_GPIO_IN_REG, RTC_GPIO_IN_NEXT_S + 9, 1) // RTC_GPIO_9 == GPIO_32
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.endm
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.macro read_SDA // Return current level of SDA line, 0 or 1
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READ_RTC_REG(RTC_GPIO_IN_REG, RTC_GPIO_IN_NEXT_S + 8, 1) // RTC_GPIO_8 == GPIO_33
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.endm
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.macro set_SCL // Do not drive SCL (set pin high-impedance)
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WRITE_RTC_REG(RTC_GPIO_ENABLE_W1TC_REG, RTC_GPIO_ENABLE_W1TC_S + 9, 1, 1)
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.endm
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.macro clear_SCL // Actively drive SCL signal low
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WRITE_RTC_REG(RTC_GPIO_OUT_REG, RTC_GPIO_OUT_DATA_S + 9, 1, 0)
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// Output mode
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WRITE_RTC_REG(RTC_GPIO_ENABLE_W1TS_REG, RTC_GPIO_ENABLE_W1TS_S + 9, 1, 1)
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.endm
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.macro set_SDA // Do not drive SDA (set pin high-impedance)
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WRITE_RTC_REG(RTC_GPIO_ENABLE_W1TC_REG, RTC_GPIO_ENABLE_W1TC_S + 8, 1, 1)
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.endm
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.macro clear_SDA // Actively drive SDA signal low
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WRITE_RTC_REG(RTC_GPIO_OUT_REG, RTC_GPIO_OUT_DATA_S + 8, 1, 0)
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// Output mode
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WRITE_RTC_REG(RTC_GPIO_ENABLE_W1TS_REG, RTC_GPIO_ENABLE_W1TS_S + 8, 1, 1)
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.endm
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i2c_start_cond:
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move r2,i2c_started
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ld r0,r2,0
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jumpr not_started,1,ge
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// if started, do a restart condition
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// set SDA to 1
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set_SDA
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I2C_delay
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set_SCL
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clock_stretch: // TODO: Add timeout?
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read_SCL
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jumpr clock_stretch,1,lt
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// Repeated start setup time, minimum 4.7us
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I2C_delay
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not_started:
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// if (read_SDA() == 0) {
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// arbitration_lost();
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// }
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// SCL is high, set SDA from 1 to 0.
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clear_SDA
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I2C_delay
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clear_SCL
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move r0,1
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st r0,r2,0
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ret
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i2c_stop_cond:
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// set SDA to 0
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clear_SDA
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I2C_delay
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set_SCL
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clock_stretch_stop:
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read_SCL
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jumpr clock_stretch_stop,1,lt
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// Stop bit setup time, minimum 4us
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I2C_delay
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// if (read_SDA() == 0) {
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// arbitration_lost();
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// }
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move r2,i2c_started
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move r0,0
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st r0,r2,0
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ret
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// Write a bit to I2C bus
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i2c_write_bit:
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jumpr bit0,1,lt
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set_SDA
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jump bit1
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bit0:
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clear_SDA
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bit1:
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// SDA change propagation delay
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I2C_delay
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// Set SCL high to indicate a new valid SDA value is available
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set_SCL
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// Wait for SDA value to be read by slave, minimum of 4us for standard mode
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I2C_delay
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clock_stretch_write:
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read_SCL
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jumpr clock_stretch_write,1,lt
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// SCL is high, now data is valid
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// If SDA is high, check that nobody else is driving SDA
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// if (bit && (read_SDA() == 0)) {
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// arbitration_lost();
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// }
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// Clear the SCL to low in preparation for next change
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clear_SCL
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ret
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// Read a bit from I2C bus
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i2c_read_bit:
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// Let the slave drive data
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set_SDA
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// Wait for SDA value to be written by slave, minimum of 4us for standard mode
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I2C_delay
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// Set SCL high to indicate a new valid SDA value is available
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set_SCL
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clock_stretch_read:
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read_SCL
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jumpr clock_stretch_read,1,lt
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// Wait for SDA value to be written by slave, minimum of 4us for standard mode
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I2C_delay
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// SCL is high, read out bit
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read_SDA
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// Set SCL low in preparation for next operation
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clear_SCL
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ret // bit in r0
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// Write a byte to I2C bus. Return 0 if ack by the slave.
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i2c_write_byte:
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stage_rst
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next_bit:
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and r0,r2,0x80
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psr
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jump i2c_write_bit
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lsh r2,r2,1
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stage_inc 1
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jumps next_bit,8,lt
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psr
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jump i2c_read_bit
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ret // nack
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// Read a byte from I2C bus
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i2c_read_byte:
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push r2
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move r2,0
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stage_rst
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next_bit_read:
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psr
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jump i2c_read_bit
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lsh r2,r2,1
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or r2,r2,r0
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stage_inc 1
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jumps next_bit_read,8,lt
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pop r0
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psr
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jump i2c_write_bit
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move r0,r2
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ret
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‎main/ulp/stack.S

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/*
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* ULP stack and subroutine macros
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*/
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.macro push rx
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st \rx,r3,0
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sub r3,r3,1
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.endm
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.macro pop rx
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add r3,r3,1
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ld \rx,r3,0
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.endm
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// Prepare subroutine jump, uses scratch register sr
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.macro psr sr=r1 pos=.
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.set _next2,(\pos+16)
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move \sr,_next2
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push \sr
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.endm
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// Return from subroutine
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.macro ret sr=r1
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pop \sr
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jump \sr
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.endm

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