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Add an example that uses burst APIs (#512)
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uses i2c_write_burst_blocking and i2c_read_burst_blocking
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peterharperuk authored Nov 22, 2024
1 parent ee332b5 commit 70222a8
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1 change: 1 addition & 0 deletions README.md
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Expand Up @@ -133,6 +133,7 @@ App|Description
[pcf8523_i2c](i2c/pcf8523_i2c) | Read time and date values from a real time clock. Set current time and alarms on it.
[ht16k33_i2c](i2c/ht16k33_i2c) | Drive a 4 digit 14 segment LED with an HT16K33.
[slave_mem_i2c](i2c/slave_mem_i2c) | i2c slave example where the slave implements a 256 byte memory
[slave_mem_i2c_burst](i2c/slave_mem_i2c) | i2c slave example where the slave implements a 256 byte memory. This version inefficiently writes each byte in a separate call to demonstrate read and write burst mode.

### Interpolator

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11 changes: 11 additions & 0 deletions i2c/slave_mem_i2c/CMakeLists.txt
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Expand Up @@ -8,3 +8,14 @@ target_link_libraries(slave_mem_i2c
)
pico_add_extra_outputs(slave_mem_i2c)
example_auto_set_url(slave_mem_i2c)

add_executable(slave_mem_i2c_burst
slave_mem_i2c_burst.c
)
target_link_libraries(slave_mem_i2c_burst
pico_i2c_slave
hardware_i2c
pico_stdlib
)
pico_add_extra_outputs(slave_mem_i2c_burst)
example_auto_set_url(slave_mem_i2c_burst)
152 changes: 152 additions & 0 deletions i2c/slave_mem_i2c/slave_mem_i2c_burst.c
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@@ -0,0 +1,152 @@
/*
* Copyright (c) 2021 Valentin Milea <[email protected]>
* Copyright (c) 2023 Raspberry Pi (Trading) Ltd.
*
* SPDX-License-Identifier: BSD-3-Clause
*/

#include <hardware/i2c.h>
#include <pico/i2c_slave.h>
#include <pico/stdlib.h>
#include <stdio.h>
#include <string.h>

static const uint I2C_SLAVE_ADDRESS = 0x17;
static const uint I2C_BAUDRATE = 100000; // 100 kHz

#ifdef i2c_default
// For this example, we run both the master and slave from the same board.
// You'll need to wire pin GP4 to GP6 (SDA), and pin GP5 to GP7 (SCL).
static const uint I2C_SLAVE_SDA_PIN = PICO_DEFAULT_I2C_SDA_PIN; // 4
static const uint I2C_SLAVE_SCL_PIN = PICO_DEFAULT_I2C_SCL_PIN; // 5
static const uint I2C_MASTER_SDA_PIN = 6;
static const uint I2C_MASTER_SCL_PIN = 7;

// The slave implements a 256 byte memory. To write a series of bytes, the master first
// writes the memory address, followed by the data. The address is automatically incremented
// for each byte transferred, looping back to 0 upon reaching the end. Reading is done
// sequentially from the current memory address.
static struct
{
uint8_t mem[256];
uint8_t mem_address;
bool mem_address_written;
} context;

// Our handler is called from the I2C ISR, so it must complete quickly. Blocking calls /
// printing to stdio may interfere with interrupt handling.
static void i2c_slave_handler(i2c_inst_t *i2c, i2c_slave_event_t event) {
switch (event) {
case I2C_SLAVE_RECEIVE: // master has written some data
if (!context.mem_address_written) {
// writes always start with the memory address
uint8_t by = i2c_read_byte_raw(i2c);
context.mem_address = by;
context.mem_address_written = true;
} else {
// save into memory
uint8_t by = i2c_read_byte_raw(i2c);
context.mem[context.mem_address] = by;
context.mem_address++;
}
break;
case I2C_SLAVE_REQUEST: // master is requesting data
// load from memory
i2c_write_byte_raw(i2c, context.mem[context.mem_address]);
context.mem_address++;
break;
case I2C_SLAVE_FINISH: // master has signalled Stop / Restart
context.mem_address_written = false;
break;
default:
break;
}
}

static void setup_slave() {
gpio_init(I2C_SLAVE_SDA_PIN);
gpio_set_function(I2C_SLAVE_SDA_PIN, GPIO_FUNC_I2C);
gpio_pull_up(I2C_SLAVE_SDA_PIN);

gpio_init(I2C_SLAVE_SCL_PIN);
gpio_set_function(I2C_SLAVE_SCL_PIN, GPIO_FUNC_I2C);
gpio_pull_up(I2C_SLAVE_SCL_PIN);

i2c_init(i2c0, I2C_BAUDRATE);
// configure I2C0 for slave mode
i2c_slave_init(i2c0, I2C_SLAVE_ADDRESS, &i2c_slave_handler);
}

static void run_master() {
gpio_init(I2C_MASTER_SDA_PIN);
gpio_set_function(I2C_MASTER_SDA_PIN, GPIO_FUNC_I2C);
// pull-ups are already active on slave side, this is just a fail-safe in case the wiring is faulty
gpio_pull_up(I2C_MASTER_SDA_PIN);

gpio_init(I2C_MASTER_SCL_PIN);
gpio_set_function(I2C_MASTER_SCL_PIN, GPIO_FUNC_I2C);
gpio_pull_up(I2C_MASTER_SCL_PIN);

i2c_init(i2c1, I2C_BAUDRATE);

for (uint8_t mem_address = 0;; mem_address = (mem_address + 32) % 256) {
char msg[32];
snprintf(msg, sizeof(msg), "Hello, I2C slave! - 0x%02X", mem_address);
uint8_t msg_len = strlen(msg);

uint8_t buf[32];
buf[0] = mem_address;
memcpy(buf + 1, msg, msg_len);
// write message at mem_address
printf("Write at 0x%02X: '%s'\n", mem_address, msg);
for(int i = 0; i < (1 + msg_len); i++) {
int count;
if (i < (1 + msg_len - 1)) {
count = i2c_write_burst_blocking(i2c1, I2C_SLAVE_ADDRESS, &buf[i], 1);
sleep_ms(1); // gratuitous sleep for demonstration purposes - don't do this in real code!
} else if (i == (1 + msg_len - 1)) {
count = i2c_write_blocking(i2c1, I2C_SLAVE_ADDRESS, &buf[i], 1, false);
}
if (count != 1) {
puts("Couldn't write to slave, please check your wiring!");
return;
}
}

// seek to mem_address
int count = i2c_write_blocking(i2c1, I2C_SLAVE_ADDRESS, buf, 1, true);
hard_assert(count == 1);

// partial read
for(int i = 0; i < msg_len; i++) {
if (count < (msg_len - 1)) {
count = i2c_read_burst_blocking(i2c1, I2C_SLAVE_ADDRESS, buf + i, 1);
sleep_ms(1); // gratuitous sleep for demonstration purposes - don't do this in real code!
} else {
count = i2c_read_blocking(i2c1, I2C_SLAVE_ADDRESS, buf + i, 1, false);
}
hard_assert(count == 1);
}
buf[msg_len] = '\0';
printf("Read at 0x%02X: '%s'\n", mem_address, buf);
hard_assert(memcmp(buf, msg, msg_len) == 0);

puts("");
sleep_ms(2000);
}
}
#endif

int main() {
stdio_init_all();
#if !defined(i2c_default) || !defined(PICO_DEFAULT_I2C_SDA_PIN) || !defined(PICO_DEFAULT_I2C_SCL_PIN)
#warning i2c / slave_mem_i2c example requires a board with I2C pins
puts("Default I2C pins were not defined");
return 0;
#else
puts("\nI2C slave example");

setup_slave();
run_master();
#endif
}

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