Direct memory access controller (DMA) RM0440
412/2126 RM0440 Rev 4
Addressing AHB peripherals not supporting byte/half-word write transfers
When the DMA controller initiates an AHB byte or half-word write transfer, the data are
duplicated on the unused lanes of the AHB master 32-bit data bus (HWDATA[31:0]).
When the AHB slave peripheral does not support byte or half-word write transfers and does
not generate any error, the DMA controller writes the 32 HWDATA bits as shown in the two
examples below:
• To write the half-word 0xABCD, the DMA controller sets the HWDATA bus to
0xABCDABCD with a half-word data size (HSIZE = HalfWord in AHB master bus).
• To write the byte 0xAB, the DMA controller sets the HWDATA bus to 0xABABABAB
with a byte data size (HSIZE = Byte in the AHB master bus).
Assuming the AHB/APB bridge is an AHB 32-bit slave peripheral that does not take into
account the HSIZE data, any AHB byte or half-word transfer is changed into a 32-bit APB
transfer as described below:
• An AHB byte write transfer of 0xB0 to one of the 0x0, 0x1, 0x2 or 0x3 addresses, is
converted to an APB word write transfer of 0xB0B0B0B0 to the 0x0 address.
• An AHB half-word write transfer of 0xB1B0 to the 0x0 or 0x2 addresses, is converted to
an APB word write transfer of 0xB1B0B1B0 to the 0x0 address.
12.4.7 DMA error management
A DMA transfer error is generated when reading from or writing to a reserved address
space. When a DMA transfer error occurs during a DMA read or write access, the faulty
channel x is automatically disabled through a hardware clear of its EN bit in the
corresponding DMA_CCRx register.
The TEIFx bit of the DMA_ISR register is set. An interrupt is then generated if the TEIE bit of
the DMA_CCRx register is set.
The EN bit of the DMA_CCRx register can not be set again by software (channel x re-
activated) until the TEIFx bit of the DMA_ISR register is cleared (by setting the CTEIFx bit of
the DMA_IFCR register).
When the software is notified with a transfer error over a channel which involves a
peripheral, the software has first to stop this peripheral in DMA mode, in order to disable any
pending or future DMA request. Then software may normally reconfigure both DMA and the
peripheral in DMA mode for a new transfer.
To Next Page
Loading...
Need help?
General
