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Silicon Updates

SPRZ293A—November 2009 TMS320C6457 Fixed-Point Digital Signal Processor Silicon Errata 11

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Upon polling, if the value of the COMPACTV field is greater than a certain threshold

(0x20 is suggested), then the DSP should program the TC with a COMPACTV

decrement transfer. Upon completion of that transfer (as signaled in the CC IPR

decrement transfer submitted until the value of the counter is less than the threshold.

Note—Care must be taken such that the software does not over-decrement the

counter because at the time of polling, multiple requests may be in flight in the

system and may result in additional decrements compared to the current

observed value. If too many decrements occur, the counter may roll under

from 0x0 to 0x3F and accidentally result in saturation of the counter. This is

why a value of 0x20 is suggested as the threshold value (sufficiently large with

respect to the number of actual requests that may be outstanding).

This workaround requires that a specific TC instance is dedicated to the COMPACTV

decrement transfer. The reason is that, depending on the nature of the traffic on a given

queue/TC, it may be difficult to control the timing of the normal CC TR submission to

that TC versus the DSP programming of that TC. There is no hardware protection to

prevent corruption of the TC registers in the case that both CC and DSP software

attempt to program the TC simultaneously.

For the base addresses of the TCs, see the TMS320C6457 Fixed Point Digital Signal

Processor data manual (literature number SPRS582). A brief summary of the TC

registers to be configured is provided in Table 4.

Prog Set Options Register

The Prog Set Option register is shown in Table 4. The TCINTEN bit should be set to

0x1. The TCC code should be set to some known value that is not used by other requests

in the system. The other fields should be set to 0x0. Upon completion of the transfer,

the TCC value will be set in the corresponding bit in the IPR/IPRH registers. The

software should poll for this bit in the IPR/IPRH registers and then clear it with the

ICR/ICRH registers before programming the next COMPACTV decrement transfer.

Table 4 TC Registers Summary

1. The five registers listed in Table 4 should be written in the sequence shown (i.e., top to bottom). The last write, to the Prog Set

B-Dim Idx register, triggers the transfer.

Address Register Description Suggested Value

TCx Base + 0x0200 Prog Set Options See the Prog Set Options Register description below

TCx Base + 0x0204 Prog Set Src Address See Prog Set Src/Dst Address Register description below

TCx Base + 0x0208 Prog Set Count 0x00010004 (ACNT = 4 and BCNT = 1)

TCx Base + 0x020C Prog Set Dst Address See Prog Set Src/Dst Address Register description below

TCx Base + 0x0210 Prog Set B-Dim Idx 0x0 (don't care because BCNT = 1). Writing to the PBIDX register

triggers the transfer. Thus, this register should be written.

End of Table 4

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