Merge pull request #582 from espway/i2c-timing-calculation
i2c: revise timing calculation
This commit is contained in:
Ruslan V. Uss
GitHub
commit
a89417e26e
2 changed files with 90 additions and 36 deletions
104
extras/i2c/i2c.c
104
extras/i2c/i2c.c
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@ -37,29 +37,18 @@
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#define debug(fmt, ...)
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#endif
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// The following array contains delay values for different frequencies.
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// These were tuned to match the specified SCL frequency on average.
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// The tuning was done using GCC 5.2.0 with -O2 optimization.
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const static uint8_t i2c_freq_array[][2] = {
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// Delay loop takes four CPU clock cycles per round
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#define DELAY_LOOPS_PER_US_160MHZ 40
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// The value for 80 MHz is half the above
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// Constant overhead per I2C clock cycle in terms of delay loop rounds.
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// If timing is changed by some code change, these will require tuning.
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#if I2C_USE_GPIO16 == 1
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[I2C_FREQ_80K] = {230, 107},
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[I2C_FREQ_100K] = {180, 82},
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[I2C_FREQ_400K] = {30, 7},
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[I2C_FREQ_500K] = {20, 1},
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[I2C_FREQ_600K] = {13, 0},
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[I2C_FREQ_800K] = {5, 0},
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[I2C_FREQ_1000K] = {1, 0}
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#define DELAY_OVERHEAD_80MHZ 18
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#define DELAY_OVERHEAD_160MHZ 20
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#else
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[I2C_FREQ_80K] = {235, 112},
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[I2C_FREQ_100K] = {185, 88},
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[I2C_FREQ_400K] = {36, 13},
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[I2C_FREQ_500K] = {25, 8},
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[I2C_FREQ_600K] = {20, 5},
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[I2C_FREQ_800K] = {11, 1},
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[I2C_FREQ_1000K] = {5, 0},
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[I2C_FREQ_1300K] = {1, 0}
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#define DELAY_OVERHEAD_80MHZ 12
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#define DELAY_OVERHEAD_160MHZ 14
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#endif
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};
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// Bus settings
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typedef struct i2c_bus_description
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@ -71,7 +60,8 @@ typedef struct i2c_bus_description
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uint32_t g_scl_mask; // SCL pin mask
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uint32_t g_sda_mask; // SDA pin mask
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#endif
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i2c_freq_t frequency; // Frequency
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uint8_t delay_80;
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uint8_t delay_160;
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uint8_t delay;
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bool started;
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bool flag;
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@ -86,7 +76,28 @@ inline bool i2c_status(uint8_t bus)
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return i2c_bus[bus].started;
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}
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static uint32_t freq_t_to_hz(i2c_freq_t freq)
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{
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switch (freq)
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{
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case I2C_FREQ_80K: return 80000;
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case I2C_FREQ_100K: return 100000;
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case I2C_FREQ_400K: return 400000;
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case I2C_FREQ_500K: return 500000;
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case I2C_FREQ_600K: return 600000;
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case I2C_FREQ_800K: return 800000;
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case I2C_FREQ_1000K: return 1000000;
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case I2C_FREQ_1300K: return 1300000;
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}
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return 80000;
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}
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int i2c_init(uint8_t bus, uint8_t scl_pin, uint8_t sda_pin, i2c_freq_t freq)
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{
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return i2c_init_hz(bus, scl_pin, sda_pin, freq_t_to_hz(freq));
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}
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int i2c_init_hz(uint8_t bus, uint8_t scl_pin, uint8_t sda_pin, uint32_t freq)
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{
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if (bus >= I2C_MAX_BUS) {
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debug("Invalid bus");
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@ -115,8 +126,6 @@ int i2c_init(uint8_t bus, uint8_t scl_pin, uint8_t sda_pin, i2c_freq_t freq)
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i2c_bus[bus].g_scl_mask = BIT(scl_pin);
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i2c_bus[bus].g_sda_mask = BIT(sda_pin);
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#endif
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i2c_bus[bus].frequency = freq;
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i2c_bus[bus].clk_stretch = I2C_DEFAULT_CLK_STRETCH;
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// Just to prevent these pins floating too much if not connected.
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@ -130,19 +139,48 @@ int i2c_init(uint8_t bus, uint8_t scl_pin, uint8_t sda_pin, i2c_freq_t freq)
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gpio_write(scl_pin, 1);
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gpio_write(sda_pin, 1);
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// Prevent user, if frequency is high
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if (sdk_system_get_cpu_freq() == SYS_CPU_80MHZ)
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if (i2c_freq_array[i2c_bus[bus].frequency][1] == 0) {
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debug("Frequency not supported");
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return -ENOTSUP;
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}
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// Inform user if the desired frequency is not supported.
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if (i2c_set_frequency_hz(bus, freq) != 0) {
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debug("Frequency not supported");
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return -ENOTSUP;
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}
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return 0;
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}
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void i2c_set_frequency(uint8_t bus, i2c_freq_t freq)
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int i2c_set_frequency(uint8_t bus, i2c_freq_t freq)
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{
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i2c_bus[bus].frequency = freq;
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return i2c_set_frequency_hz(bus, freq_t_to_hz(freq));
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}
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int i2c_set_frequency_hz(uint8_t bus, uint32_t freq)
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{
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if (freq == 0) return -EINVAL;
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uint32_t tick_count = (1000000UL * DELAY_LOOPS_PER_US_160MHZ) / (2 * freq);
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bool not_ok = false;
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int32_t delay_80 = tick_count / 2 - DELAY_OVERHEAD_80MHZ;
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if (delay_80 > 255) {
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delay_80 = 255;
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not_ok = true;
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} else if (delay_80 < 0) {
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delay_80 = 0;
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not_ok = true;
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}
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int32_t delay_160 = tick_count - DELAY_OVERHEAD_160MHZ;
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if (delay_160 > 255) {
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delay_160 = 255;
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not_ok = true;
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} else if (delay_160 < 0) {
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delay_160 = 0;
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not_ok = true;
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}
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i2c_bus[bus].delay_80 = delay_80;
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i2c_bus[bus].delay_160 = delay_160;
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return not_ok ? -EINVAL : 0;
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}
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void i2c_set_clock_stretch(uint8_t bus, uint32_t clk_stretch)
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@ -219,9 +257,9 @@ static inline void set_sda(uint8_t bus)
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void i2c_start(uint8_t bus)
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{
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if (sdk_system_get_cpu_freq() == SYS_CPU_160MHZ)
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i2c_bus[bus].delay = i2c_freq_array[i2c_bus[bus].frequency][0];
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i2c_bus[bus].delay = i2c_bus[bus].delay_160;
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else
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i2c_bus[bus].delay = i2c_freq_array[i2c_bus[bus].frequency][1];
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i2c_bus[bus].delay = i2c_bus[bus].delay_80;
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if (i2c_bus[bus].started) { // if started, do a restart cond
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// Set SDA to 1
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@ -66,9 +66,7 @@ typedef enum
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I2C_FREQ_600K,
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I2C_FREQ_800K,
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I2C_FREQ_1000K,
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#if I2C_USE_GPIO16 == 0
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I2C_FREQ_1300K
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#endif
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} i2c_freq_t;
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/**
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@ -93,12 +91,30 @@ typedef struct i2c_dev
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*/
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int i2c_init(uint8_t bus, uint8_t scl_pin, uint8_t sda_pin, i2c_freq_t freq);
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/**
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* Init bitbanging I2C driver on given pins
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* @param bus Bus i2c selection
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* @param scl_pin SCL pin for I2C
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* @param sda_pin SDA pin for I2C
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* @param freq frequency of bus in hertz
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* @param clk_stretch I2C clock stretch. I2C_DEFAULT_CLK_STRETCH would be good in most cases
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* @return Non-zero if error occured
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*/
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int i2c_init_hz(uint8_t bus, uint8_t scl_pin, uint8_t sda_pin, uint32_t freq);
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/**
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* Change bus frequency
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* @param bus Bus i2c selection
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* @param freq frequency of bus (ex : I2C_FREQ_400K)
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*/
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void i2c_set_frequency(uint8_t bus, i2c_freq_t freq);
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int i2c_set_frequency(uint8_t bus, i2c_freq_t freq);
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/**
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* Change bus frequency
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* @param bus Bus i2c selection
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* @param freq frequency of bus in hertz
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*/
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int i2c_set_frequency_hz(uint8_t bus, uint32_t freq);
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/**
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* Change clock stretch
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