Hello! This is the first time I'm using an STM32L0 (...11F4Ux) and also the first time I've tried implementing an I2C IRQ Handler. The code snippet mostly works, but there's a bug in which a READ commands sends data from the previously requested register, giving bad data. Basically, the data I receive is old by 1 request, which tells me this IRQ Handler is not handling the repeated start correctly. The exception to this is that the very first READ command is correct when I start up I2C tools on a RP5. I've been trying to figure out this bug for a couple of days now, so I'd really appreciate any help from more experience developers, thank you!
Details:
- Flash limited to 16KB, so using LL drivers only
- This snippet is broken out into its own file and is called by I2C1_IRQHandler();
- WRITE commands work perfectly fine
- When placing a stop at the LL_I2C_TransmitData8(I2C1, tx_val);, I get data from my previous command without this line executing.
- Master: Raspberry Pi 5 Compute module using I2Ctools. (i.e. i2cget -y 1 0x21 0x02 - read ADC BATT)
I'm 99% certain the bug exist in the handler itself but I can't seem to narrow it down. Somehow data is being stored between READ commands.
void I2C1_Slave_Init(void)
{
/* Enable clocks */
LL_APB1_GRP1_EnableClock(LL_APB1_GRP1_PERIPH_I2C1);
LL_IOP_GRP1_EnableClock(LL_IOP_GRP1_PERIPH_GPIOA);
/* Configure GPIO: PA9=SCL, PA10=SDA */
LL_GPIO_InitTypeDef GPIO_InitStruct = {0};
GPIO_InitStruct.Pin = LL_GPIO_PIN_9 | LL_GPIO_PIN_10;
GPIO_InitStruct.Mode = LL_GPIO_MODE_ALTERNATE;
GPIO_InitStruct.Speed = LL_GPIO_SPEED_FREQ_HIGH;
GPIO_InitStruct.OutputType = LL_GPIO_OUTPUT_OPENDRAIN;
GPIO_InitStruct.Pull = LL_GPIO_PULL_NO; // Must have pull-ups for I2C
GPIO_InitStruct.Alternate = LL_GPIO_AF_1;
LL_GPIO_Init(GPIOA, &GPIO_InitStruct);
/* Configure I2C1 */
LL_I2C_InitTypeDef I2C_InitStruct = {0};
I2C_InitStruct.PeripheralMode = LL_I2C_MODE_I2C;
I2C_InitStruct.Timing = 0x20404768; // 100 kHz @ 16 MHz HSI
I2C_InitStruct.AnalogFilter = LL_I2C_ANALOGFILTER_ENABLE;
I2C_InitStruct.DigitalFilter = 0;
I2C_InitStruct.OwnAddress1 = I2C_SLAVE_ADDR;
I2C_InitStruct.TypeAcknowledge = LL_I2C_ACK;
I2C_InitStruct.OwnAddrSize = LL_I2C_OWNADDRESS1_7BIT;
LL_I2C_Init(I2C1, &I2C_InitStruct);
LL_I2C_EnableAutoEndMode(I2C1);
LL_I2C_EnableClockStretching(I2C1);
/* Enable interrupts */
LL_I2C_EnableIT_ADDR(I2C1);
LL_I2C_EnableIT_RX(I2C1);
LL_I2C_EnableIT_TX(I2C1);
LL_I2C_EnableIT_STOP(I2C1);
/* NVIC */
NVIC_SetPriority(I2C1_IRQn, 0);
NVIC_EnableIRQ(I2C1_IRQn);
/* Enable I2C1 peripheral */
LL_I2C_Enable(I2C1);
}
/* IRQ Handler */
void I2C1_Slave_IRQHandler(void)
{
/* --- Address Match --- */
if (LL_I2C_IsActiveFlag_ADDR(I2C1))
{
uint32_t direction = LL_I2C_GetTransferDirection(I2C1);
LL_I2C_ClearFlag_ADDR(I2C1);
i2c_rx_index = 0;
i2c_tx_index = 0;
if (direction == LL_I2C_DIRECTION_READ)
{
/* Repeated START for read phase.
* Keep using last i2c_reg_pointer (don’t reset it). */
i2c_tx_len = 1;
}
}
/* --- Data Received from Master (Write Phase) --- */
if (LL_I2C_IsActiveFlag_RXNE(I2C1))
{
uint8_t byte = LL_I2C_ReceiveData8(I2C1);
if (i2c_rx_index == 0)
{
/* First byte = register address */
i2c_reg_pointer = byte;
}
else if (i2c_rx_index == 1)
{
/* Second byte = data to write */
uint8_t val = byte;
switch (i2c_reg_pointer)
{
case REG_5V_CONTROL:
g_process_5v_off = val ? 1 : 0;
i2c_buf[REG_5V_CONTROL] = val;
break;
case REG_24V_CONTROL:
g_process_24v = val ? 1 : 0;
i2c_buf[REG_24V_CONTROL] = val;
break;
/* Read-only registers */
case REG_ADC_BATT:
case REG_CHARGE_STAT:
case REG_CHECK_BTTN:
default:
break;
}
}
i2c_rx_index++;
}
/* --- Master Requesting Data (Read Phase) --- */
if (LL_I2C_IsActiveFlag_TXIS(I2C1))
{
uint8_t tx_val = 0x00;
switch (i2c_reg_pointer)
{
case REG_ADC_BATT:
tx_val = i2c_buf[REG_ADC_BATT];
break;
case REG_CHARGE_STAT:
tx_val = i2c_buf[REG_CHARGE_STAT];
break;
case REG_CHECK_BTTN:
tx_val = i2c_buf[REG_CHECK_BTTN];
i2c_buf[REG_CHECK_BTTN] = 0;
btn_pressed_awake = 0;
break;
/* Default to return the buffer content for other regs */
default:
tx_val = i2c_buf[i2c_reg_pointer];
break;
}
LL_I2C_TransmitData8(I2C1, tx_val);
}
/* --- STOP Condition (End of Transaction) --- */
if (LL_I2C_IsActiveFlag_STOP(I2C1))
{
LL_I2C_ClearFlag_STOP(I2C1);
i2c_rx_index = 0;
i2c_tx_index = 0;
i2c_tx_len = 0;
}
}
