ST90158 - MULTIFUNCTION TIMER (MFT)
MULTIFUNCTION TIMER (Cont’d)
9.3.5.6 DMA End Of Block Interrupt Routine
– 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.
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.
9.3.5.7 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.
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 9.3.5.7).
– Read the corresponding Overrun bit: this con-
firms that no DMA request has been lost in the
meantime.
9.3.6 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.
– Reset the corresponding pending bit.
– Reenable DMA with the corresponding DMA
mask bit (must always be done after resetting
the pending bit)
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