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I2C DMA data sizes

Question asked by grove.kevin on Jun 11, 2013
Latest reply on Jun 13, 2013 by Clive One
Using a STM32L152RB

I'm trying to send some data out on the I2C bus using DMA, but I can't quite get the data to transmit like I expected.

This is how I'm initializing the DMA.  My memory source is a 4-element array of 32-bit values (defined uint32_t i2cTxBuffer[]), and I am setting the peripheral to an 8-bit data size.
/* DMA1 channel 4 configuration ---------------------------------------------*/
/* Enable DMA1 clock -------------------------------------------------------*/
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA1, ENABLE);
DMA_InitStructure_I2cTx.DMA_PeripheralBaseAddr = (uint32_t) I2C2_DR_ADDR;
DMA_InitStructure_I2cTx.DMA_MemoryBaseAddr = (uint32_t) i2cTxBuffer;                
DMA_InitStructure_I2cTx.DMA_DIR = DMA_DIR_PeripheralDST;                  
DMA_InitStructure_I2cTx.DMA_BufferSize = 4;
DMA_InitStructure_I2cTx.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
DMA_InitStructure_I2cTx.DMA_MemoryInc = DMA_MemoryInc_Enable;
DMA_InitStructure_I2cTx.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;
DMA_InitStructure_I2cTx.DMA_MemoryDataSize = DMA_MemoryDataSize_Word;
DMA_InitStructure_I2cTx.DMA_Mode = DMA_Mode_Normal;
DMA_InitStructure_I2cTx.DMA_Priority = DMA_Priority_High;
DMA_InitStructure_I2cTx.DMA_M2M = DMA_M2M_Disable;
DMA_Init(DMA1_Channel4, &DMA_InitStructure_I2cTx);
/* Enable DMA1 Channel6 Transfer Complete interrupt */
DMA_ITConfig(DMA1_Channel4, DMA_IT_HT, ENABLE);
DMA_ITConfig(DMA1_Channel4, DMA_IT_TC, ENABLE);
/* Enable DMA1 channel6 IRQ Channel */
NVIC_InitStructure.NVIC_IRQChannel = DMA1_Channel4_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;

However, when the DMA takes over, it seems to be sending only the least-significant 16 bits of each 32-bit piece of data.  I'm wondering why this is.  Is a 'word' considered only 16 bits on this micro?  Is it an I2C thing?  I can't seem to find any info in the manual.

Thanks in advance!

EDIT:  Ignore the comments that say 'Channel 6'.  Those were just copy-pasted.  Also, I realize I could accomplish what I want by simply using an 8-element array of 16-bit values, I just don't want to split the data if at all possible.