RM0319 datasheet(61/368 Pages) STMICROELECTRONICS

61 / 368 page

RM0319

Multiport DDR controller (MPMC)

Doc ID 022640 Rev 3

61/368

WRAPx transactions with a starting address that is not aligned to the total number of bytes

in the burst (bytes-per-beat times the number of beats) are issued as two separate memory

controller core transactions as shown in Figure 17. The first transaction has a starting

address which is the same as the WRAP transaction starting address and its byte count is

the number of bytes from the starting address to the wrap boundary. The second transaction

has a starting address which is aligned to the byte count in the WRAPx transfer and its byte

count is the number of bytes from the wrapped address back to the starting address. This

means that an AHB WRAP instruction is divided into two core transactions, one for the non-

wrapped portion of the transaction and one for the wrapped portion. The starting address

determines whether the WRAP transaction will actually wrap or not. A wrap transaction with

an aligned address is equivalent to an INCRx command and is treated as such by the AHB

port.

Figure 17.

WRAPx effective transaction

Full-Size INCR transactions

Since the MPMC core bus protocol does not support transactions of an unspecified length,

AHB INCR transactions require special handling by the AHB port logic. Each AHB port

contains a pair of programmable parameters for determining the length of a command that

will be issued to the MPMC core when an INCR command is issued to the AHB port. These

parameters are ahbX_wrcnt and ahbX_rdcnt and they hold the programmed size used for

an unspecified length WRITE and a READ command length in bytes for port X when this

type of command is issued to the core.

The value defined in these parameters should be a multiple of the number of bytes in a data

word for the core. If that is not the case, the parameter values will automatically be truncated

to the data word boundary. Clearing these parameters will cause the port to issue

commands of 0 length to the core, which the core interprets as the pre-configured value of

1024.

The values for the ahbX_wrcnt and ahbX_rdcnt parameters should be chosen carefully and

should be based on the average length of an INCR transaction expected from the AHB

master. If the values are programmed too low, the AHB port must issue a large number of

small core transactions that may fill up the command queue and reduce system

performance. A full queue may also inhibit higher priority requests from meeting their

latency requirements. On the other hand, if the values for the parameters are programmed

Starting

Address

Wrap

Address

The command wraps at address:

(Starting Address+X)-Modules(Starting Address/X)

Where X is the Wrap Size in WARPx

Starting Address-Modules (Starting Address/X)

Where X is the Wrap Size in WARPx

WRAPx Command

Length = X*ahbX_HSIZE

Transaction #1

Transaction #2

Memory Page Containing Starting Address

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