Peripheral Control Module

The value written to the device select DS<3:0> field specifies which DMA request this channel responds to. The device datum width (DW) field value is fixed for each device type and indicates whether the device’s data port is one or two bytes wide. If the datum width is programmed incorrectly for a particular device select, then the results are unpredictable.

The device burst size (BS) field value is fixed for each device type. It indicates how many beats of the datum width are transferred each time the device requests service. This value is chosen based on the FIFO size of the particular device. If the burst size is programmed incorrectly for a particular device select, then the results are unpredictable.

The device endianess E field value indicates the byte ordering within a word when data is read from or written to memory. If the E bit is zero, then memory is assumed to be little endian. If the bit is one, then memory is assumed to be big endian. The following figure shows big and little endian DMA transfers.

Figure 11-2. Big and Little Endian DMA Transfers

Big Endian DMA Transfers

D<31> D<0>

3 2 1 0 from memory

DMA

Controller

Little Endian DMA Transfers

D<31> D<0>

3 2 1 0 from memory

DMA

Controller

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0

 

3

 

3

2

 

1

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

 

2

 

 

 

 

 

 

 

1

0

 

3

2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2

 

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3

 

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

From

 

To

To

From

Half-word wide

Byte-wide

 

Device

 

 

Device

32 3 2

10 1 0

From To

Half-word wide

Device

3 0

2 1

1 2

0 3

To From

Byte-wide

Device

A6893-01

The device transfer direction (RW) field indicates the direction of the transfer. A zero indicates that the transfer is a write (with respect to the device) and that the flow of data will be from memory to the device. If the RW field is programmed to a one, then the transfer is a read and the flow of data will be from the device to memory. The transfer direction is fixed for each device type. If the burst size is programmed incorrectly for a particular device select, then the results are unpredictable.

SA-1100 Developer’s Manual

11-9

Page 159
Image 159
Intel SA-1100 D31 D0 1 0 from memory, Controller From Half-word wide, Device From To Half-word wide To From Byte-wide