Add initial code.

README.md

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+# i2c slave based on stm32
+This is an i2c slave based on stm32. This implements a simple math calculator
+for doing addition, subtraction and multiplication of given two numbers.
+
+## how to compile
+
+Modify `meson.build` according to your needs.
+
+`libocm3Path` - libopencm3 directory path
+
+You need to issue `./build.sh` for once.
+ ```shell
+$ ./build.sh
+$ cd builddir
+```
+ninja - generates elf file.
+```shell
+$ ninja
+```
+
+ninja hex - generates hex file.
+```shell
+$ ninja hex
+```
+ninja size - gives the summary of hex file size.
+```shell
+$ ninja size
+```
+ninja upload - upload hex file to stm32 via stlink programmer.
+```shell
+$ ninja upload
+```
+
+Refer to [my blog](http://amitesh-singh.github.io/stm32/2018/01/07/making-i2c-slave-using-stm32f103.html) for more details.

build.sh

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+meson . builddir --cross-file cross-file.txt  --buildtype=minsize

cross-file.txt

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+[binaries]
+c = 'arm-none-eabi-gcc'
+cpp = 'arm-none-eabi-g++'
+ar = 'arm-none-eabi-ar'
+strip = 'arm-none-eabi-strip'
+objcopy = 'arm-none-eabi-objcopy'
+size = 'arm-none-eabi-size'
+
+[host_machine]
+system = 'linux'
+cpu_family = 'x86_64'
+cpu = 'x64'
+endian = 'little'
+
+[target_machine]
+system = 'bare-metel'
+cpu_family = 'stm32'
+cpu = 'STM32F1'
+endian = 'little'

libopencm3_f1.ld

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+MEMORY
+{
+    rom (rx) : ORIGIN = 0x08000000, LENGTH = 128K
+    ram (xrw)  : ORIGIN = 0x20000000, LENGTH = 20K
+}
+
+INCLUDE libopencm3_stm32f1.ld
+

main.cpp

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+/*
+ * math calculator i2c slave stm32
+ * Copyright (C) 2017  Amitesh Singh <[email protected]>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+extern "C"
+{
+   #include <libopencm3/cm3/common.h>
+   #include <libopencm3/stm32/rcc.h>
+   #include <libopencm3/stm32/gpio.h>
+   #include <libopencm3/stm32/i2c.h>
+   #include <libopencm3/cm3/nvic.h>
+}
+
+static void
+my_delay_1( void )
+{
+   int i = 72e6/2/4;
+
+   while( i > 0 )
+     {
+        i--;
+        __asm__( "nop" );
+     }
+}
+
+#define MYSLAVE_ADDRESS 0x32
+//Set Commands
+#define MYSLAVE_SET_REG 0x01
+//GET commands
+#define MYSLAVE_GET_ADD_RESULT 0x02
+#define MYSLAVE_GET_SUB_RESULT 0x03
+#define MYSLAVE_GET_MUL_RESULT 0x04
+
+static void
+i2c_slave_init(uint8_t ownaddress)
+{
+   rcc_periph_clock_enable(RCC_GPIOB);
+   rcc_periph_clock_enable(RCC_I2C1);
+
+   nvic_enable_irq(NVIC_I2C1_EV_IRQ);
+
+   // configure i2c pins
+   gpio_set_mode(GPIOB, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_ALTFN_OPENDRAIN,
+                 GPIO_I2C1_SDA); //PB7
+   gpio_set_mode(GPIOB, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_ALTFN_OPENDRAIN,
+                 GPIO_I2C1_SCL); //PB6
+
+   i2c_reset(I2C1);
+   i2c_peripheral_disable(I2C1);
+
+   i2c_set_speed(I2C1, i2c_speed_sm_100k, I2C_CR2_FREQ_36MHZ);
+   i2c_set_own_7bit_slave_address(I2C1, ownaddress);
+   i2c_enable_interrupt(I2C1, I2C_CR2_ITEVTEN | I2C_CR2_ITBUFEN);
+   i2c_peripheral_enable(I2C1);
+
+   // slave needs to acknowledge on receiving bytes
+   // set it after enabling Peripheral i.e. PE = 1
+   i2c_enable_ack(I2C1);
+}
+
+volatile uint8_t *read_p;
+volatile uint8_t *write_p;
+volatile uint8_t writing;
+volatile uint8_t reading;
+
+volatile uint8_t buf[3];
+volatile uint16_t val;
+
+//i2c1 event ISR
+extern "C" void i2c1_ev_isr(void)
+{
+   uint32_t sr1, sr2;
+
+   sr1 = I2C_SR1(I2C1);
+
+   if (sr1 & I2C_SR1_ADDR)
+     {
+        reading = 0;
+        read_p = buf;
+        write_p = ((volatile uint8_t *)(&val) + 1);
+        writing = 2;
+        //Clear the ADDR sequence by reading SR2.
+        sr2 = I2C_SR2(I2C1);
+        (void) sr2;
+     }
+   else if (sr1 & I2C_SR1_RxNE)
+     {
+        //ignore more than 3 bytes reading
+        if (reading > 3)
+          return;
+        //read bytes from slave
+        *read_p++ = i2c_get_data(I2C1);
+        reading++;
+     }
+   else if ((sr1 & I2C_SR1_TxE) && !(sr1 & I2C_SR1_BTF))
+     {
+        //send data to master in MSB order
+        i2c_send_data(I2C1, *write_p--);
+        writing--;
+     }
+   // done by master by sending STOP
+   //this event happens when slave is in Recv mode at the end of communication
+   else if (sr1 & I2C_SR1_STOPF)
+     {
+        i2c_peripheral_enable(I2C1);
+
+        if (buf[0] == MYSLAVE_GET_ADD_RESULT)
+          val = buf[1] + buf[2];
+        else if (buf[0] == MYSLAVE_GET_SUB_RESULT)
+          val = buf[1] - buf[2];
+        else if (buf[0] == MYSLAVE_GET_MUL_RESULT)
+          val = buf[1] * buf[2];
+     }
+   //this event happens when slave is in transmit mode at the end of communication
+   else if (sr1 & I2C_SR1_AF)
+     {
+        //(void) I2C_SR1(I2C1);
+        I2C_SR1(I2C1) &= ~(I2C_SR1_AF);
+     }
+}
+
+int main( void )
+{
+   //set STM32 to 72 MHz
+   rcc_clock_setup_in_hse_8mhz_out_72mhz();
+
+   // Enable GPIOC clock
+   rcc_periph_clock_enable(RCC_GPIOC);
+   //Set GPIO13 (inbuild led connected) to 'output push-pull'
+   gpio_set_mode(GPIOC, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL,
+                 GPIO13);
+   //switch led off
+   gpio_set(GPIOC, GPIO13);
+
+   //initialize i2c slave
+   i2c_slave_init(MYSLAVE_ADDRESS);
+
+   while( 1 )
+     {
+        gpio_toggle(GPIOC, GPIO13);
+        my_delay_1();
+     }
+}

meson.build

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+#
+ # stm32-libopencm3-meson build
+ # Copyright (C) 2017 Amitesh Singh
+ #
+ # This library is free software; you can redistribute it and/or
+ # modify it under the terms of the GNU Lesser General Public
+ # License as published by the Free Software Foundation; either
+ # version 2.1 of the License, or (at your option) any later version.
+ #
+ # This library is distributed in the hope that it will be useful,
+ # but WITHOUT ANY WARRANTY; without even the implied warranty of
+ # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ # Lesser General Public License for more details.
+ #
+ # You should have received a copy of the GNU Lesser General Public
+ # License along with this library;
+ # if not, see <http://www.gnu.org/licenses/>.
+ #
+
+
+project('stm32f1-project', 'cpp')
+
+compiler_obj = meson.get_compiler('cpp')
+
+size = find_program('arm-none-eabi-size')
+objcopy = find_program('arm-none-eabi-objcopy')
+stinfo = find_program('st-info')
+stflash = find_program('st-flash')
+
+#define libopencm3 path here
+libocm3Path = '/home/ami/repos/libopencm3'
+
+#define cpu types here
+cputype = 'cortex-m3'
+cpudefine = 'STM32F1'
+libocm3cputype = 'opencm3_stm32f1'
+
+#Add your source files here
+srcfiles = ['main.cpp']
+
+
+libocm3IncPath = libocm3Path + '/include'
+libocm3LibPath = libocm3Path + '/lib'
+
+# check for libopencm3 library
+libocm3lib_obj = compiler_obj.find_library(libocm3cputype, required: true, dirs: libocm3LibPath)
+if libocm3lib_obj.found() == true
+   message('Found libopencm3 library at ' + libocm3Path)
+else
+   error('unable to find libopencm3 library')
+endif
+
+incdir = include_directories(libocm3IncPath)
+
+stm32f1cargs = ['-Os',
+                '-ggdb',
+                '-mcpu=' + cputype,
+                '-mthumb',
+                '-msoft-float',
+                '-std=gnu++14',
+                '-Wall',
+                '-Wshadow',
+                '-ffunction-sections',
+                '-fdata-sections',
+                '-D' + cpudefine,
+                '-fno-exceptions',
+#'-I' + libocm3IncPath
+                ]
+
+stm32f1linkargs = ['-Os',
+                   '-ggdb',
+                   '-D' + cpudefine,
+                   '-fdata-sections',
+                   '-mcpu=' + cputype,
+                   '-mthumb',
+                   '-msoft-float',
+                   '-lc',
+                   '-flto',
+                   #'-T../libopencm3_f1.ld',
+                   '-T' + meson.current_source_dir() + '/libopencm3_f1.ld',
+                   '--specs=nosys.specs',
+                   '-nostartfiles',
+                   '-Wl,--gc-sections',
+                   '-L' + libocm3LibPath,
+#               '-l' + libocm3cputype,
+                  ]
+
+p = ['blink', srcfiles, stm32f1cargs, stm32f1linkargs]
+
+exe = executable(p[0], p[1],
+                 cpp_args: p[2],
+                 link_args: p[3],
+                 include_directories : incdir,
+                 dependencies: libocm3lib_obj,
+                 build_by_default: true)
+
+run_target('hex', command: [objcopy, ['-Obinary', exe.full_path(),
+           exe.full_path() + '.hex']], depends: exe)
+run_target('size', command: [size, exe.full_path(), '-B'], depends: exe)
+
+# STlink programmer related commands
+run_target('probe', command: [stinfo, '--probe'])
+run_target('upload', command: [stflash, 'write', exe.full_path() + '.hex', '0x08000000'], depends: exe)
+
+if meson.is_cross_build()
+   message('cross compiling for ' + cputype)
+   message('     \n                  ninja - generates elf file.
+                  ninja hex - generates hex file.
+                  ninja upload - upload hex file to stm32 via stlink programmer.
+                  ninja probe - probe stlink programmer.
+                  ninja size - gives the summary of hex file size.
+                  (C) Amitesh Singh ')
+endif
+