Start Addresses In A Channel; Start Address - Texas Instruments OMAP5912 Reference Manual

DSP DMA
4.6

Start Addresses in a Channel

Table 100. Registers Used to Define the Start Addresses for a DMA Transfer
4.7

Start Address

134 Direct Memory Access (DMA) Support
During a data transfer in a DMA channel, the first address at which data is read
is called the source start address. The first address to which the data is written
is called the destination start address. These are byte addresses. From the
standpoint of the DMA controller, every 8 bits in memory or I/O space has its
own address. Each channel contains registers for specifying the start
addresses, as shown in Table 100.
Channel Address Register
DMA_CSSA_L source start address (lower part)
DMA_CSSA_U source start address (upper part)
DMA_CDSA_L destination start address (lower part)
DMA_CDSA_U destination start address (upper part)
The following sections explain how to load the start address registers for
memory accesses and I/O accesses. The DMA controller can access all of the
internal and external memory and all of I/O space (which contains registers for
the DSP peripherals).
Figure 21 shows a high-level memory map for the DSP subsystem, showing
both the word addresses (23-bit addresses) used by the CPU and the byte
addresses (24-bit addresses) used by the DMA controller. To load the
source/destination start address registers:
1) Identify the correct start address. Check for any alignment constraint for
the data type; see the description for the data type bits in Section 4.23.2,
Channel Source Start Address. If you have a word address, shift it left by
1 bit to form a byte address with 24 bits. For example, convert word
address 02 4000h to byte address 04 8000h.
2) Load the 16 least significant bits (LSBs) of the byte address into
DMA_CSSA_L (for source) or DMA_CDSA_L (for destination).
3) Load the eight most significant bits (MSBs) of the byte address into the
eight LSBs of DMA_CSSA_U (for source) or DMA_CDSA_U (for
destination).
SPRU755B