ST90135 datasheet(116/190 Pages) STMICROELECTRONICS

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ST90158 - MULTIFUNCTION TIMER (MFT)

MULTIFUNCTION TIMER (Cont’d)

9.2.5.6 DMA End Of Block Interrupt Routine

An interrupt request is generated after each block

transfer (EOB) and its priority is the same as that

assigned in the usual interrupt request, for the two

channels. As a consequence, they will be serviced

only when no DMA request occurs, and will be

subject to a possible OUF Interrupt request, which

has higher priority.

The following is a typical EOB procedure (with

swap mode enabled):

– Test Toggle bit and Jump.

– Reload Pointers (odd or even depending on tog-

gle bit status).

– Reset EOB bit: this bit must be reset only after

the old pair of pointers has been restored, so

that, if a new EOB condition occurs, the next pair

of pointers is ready for swapping.

– Verify the software protection condition (see

Section 9.2.5.7).

– Read the corresponding Overrun bit: this con-

firms that no DMA request has been lost in the

meantime.

– Reset the corresponding pending bit.

– Reenable DMA with the corresponding DMA

mask bit (must always be done after resetting

the pending bit)

– Return.

WARNING: The EOB bits are read/write only for

test purposes. Writing a logical “1” by software

(when the SWEN bit is set) will cause a spurious

interrupt request. These bits are normally only re-

set by software.

9.2.5.7 DMA Software Protection

A second EOB condition may occur before the first

EOB routine is completed, this would cause a not

yet updated pointer pair to be addressed, with con-

sequent overwriting of memory. To prevent these

errors, a protection mechanism is provided, such

that the attempted setting of the EOB bit before it

has been reset by software will cause the DMA

mask on that channel to be reset (DMA disabled),

thus blocking any further DMA operation. As

shown above, this mask bit should always be

checked in each EOB routine, to ensure that all

DMA transfers are properly served.

9.2.6 Register Description

Note: In the register description on the following

pages, register and page numbers are given using

the example of Timer 0. On devices with more

than one timer, refer to the device register map for

the adresses and page numbers.

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