Bare metal, Assembly language • Re: DMA on UART0

That was the right trigger, thanks. I also noticed you need to adapt for the fact that the data register is 32 bits but only holds a single character:

Code:

    m_controlBlock->TransferInformation = (static_cast<uint32>(dreq) << RPI_DMA_TI_PERMAP_SHIFT) |                                          (RPI_DMA_DEFAULT_BURST_LENGTH << RPI_DMA_TI_BURST_LENGTH_SHIFT) |                                          RPI_DMA_TI_SRC_WIDTH | RPI_DMA_TI_SRC_INC | RPI_DMA_TI_DST_DREQ | RPI_DMA_TI_WAIT_RESP;    if (srcStride != 0)    {        // Writes are always a full 32 bit register, but we want to send a different width        // This is a.o. used for UART writes        m_controlBlock->TransferInformation |= RPI_DMA_TI_TDMODE;        m_controlBlock->TransferLength = length << RPI_DMA_TXFR_LEN_YLENGTH_SHIFT | 1 << RPI_DMA_TXFR_LEN_XLENGTH_SHIFT;    }    else    {        m_controlBlock->TransferLength = length;    }   m_controlBlock->ModeStride2D = 0;   m_controlBlock->SourceAddress = ARM_TO_GPU((uintptr)srcAddress);   m_controlBlock->DestinationAddress = dstIOAddress;   m_controlBlock->NextControlBlockAddress = 0;

So here I use a stride of 1 to make sure we only advance one byte at a time.

Thanks for the help!

Statistics: Posted by DougieLawson — Mon Sep 15, 2025 6:31 am