DSP56857 datasheet(288/662 Pages) FREESCALE

288 / 662 page

Error Conditions

5685X Digital Signal Controller User Manual, Rev. 4

11-18

Freescale Semiconductor

Figure 11-11. Missed Read of Overflow Condition

In this case, an overflow can easily be missed. Since no more SPRF interrupts can be generated

until this OVRF is serviced, it is not obvious data is being lost as more transmissions are

completed. To prevent this loss, either enable the OVRF interrupt or take another read of the

SPSCR following the read of the SPDRR. This ensures the OVRF was not set before the SPRF

was cleared. Future transmissions can set the SPRF bit. Figure 11-11 illustrates the described

process. Generally, to avoid a second SPSCR read, enable the OVRF to the core by setting the

ERRIE bit.

READ SPDRR

READ SPSCR

OVRF

SPRF

DATA 1

DATA 2

DATA 3

DATA 4

DATA 1 SETS SPRF BIT.

DSC READS SPSCR WITH SPRF BIT

DSC READS DATA 1 IN SPDRR,

DATA 2 SETS SPRF BIT.

DSC READS SPSCR WITH SPRF BIT SET

DATA 3 SETS OVRF BIT. DATA 3 IS LOST.

DSC READS DATA 2 IN SPDRR, CLEARING SPRF

DATA 4 FAILS TO SET SPRF BIT BECAUSE

CLEARING SPRF BIT.

BIT BUT NOT THE OVRF BIT.

OVRF BIT IS NOT CLEARED. DATA 4 IS LOST.

SET AND OVRF BIT CLEAR.

AND OVRF BIT CLEAR.

DSP56857 Datasheet(PDF) 288 Page - Freescale Semiconductor, Inc