PACK8 on IPIPE input

Gennadiy Kiryukhin

I can configure the CCDC to save data in 8-bit chunks without applying A-law. This way I was able to look at the raw undistorted by A-law upper 8 bits of data. How can I setup my IPIPE to read 8-bit data without the A-law? It seems like I should be able to do that because PACK8 and ALAW have separate bits. Should I set PACK8IN bit and clear IALAW bit in ther IPIE CFG register? What should be the shift value? It seems like it should be shifting by 6 bits. However, the shift goes up to 4 bits max.

The datasheet (SPRUF71A, page 57) also says that if A-law is enabled, the 10bit data is padded with 4 '0's to make it 14 bit data. From the description it sounds like the "four '0's padding" would be independent of the CFG.DATASFT value if A-law is used. What about the case where A-low is not enabled and 8-bit RAW data is linear?

Thank you.

over 14 years ago

0 Gang Hua over 14 years ago

TI__Guru 59300 points

Yes, you shall set PACK8IN=1 and IALAW=0 and you can only shift up to 4 bits.

0 Gennadiy Kiryukhin over 14 years ago in reply to Gang Hua

Expert 2800 points

If I use A-law, do I need to set the shift value?

0 Gennadiy Kiryukhin over 14 years ago in reply to Gennadiy Kiryukhin

Expert 2800 points

I am confused a bit. The diagram on page 56 of SPRUF71A shows that the shift is only used when reading 16 bit data. For 8-bit data with A-Law enabled the output is 14 bits with lower 4 bits set to 0 and upper 10 bits come from the inverse A-law transform. What is the bit format when PACK8IN is set and A-Law is cleared?

0 Gang Hua over 14 years ago in reply to Gennadiy Kiryukhin

TI__Guru 59300 points

Gennadiy Kiryukhin said:

I am confused a bit. The diagram on page 56 of SPRUF71A shows that the shift is only used when reading 16 bit data. For 8-bit data with A-Law enabled the output is 14 bits with lower 4 bits set to 0 and upper 10 bits come from the inverse A-law transform. What is the bit format when PACK8IN is set and A-Law is cleared?

Your 8-bit raw input shall be in the 8 LSBs of the 16-bit 'Data shift' block input.

- If I use A-law, do I need to set the shift value?

It depends on how you process your 8-bit raw data in IPIPE

You can shift up to 4 bits, if you want to.

That is, your 8 bits can be in 7:0, 8:1, 9:2, 10:3, or 11:4 of your 14-bit 'Data shift' block output (see Table 112).

0 Gennadiy Kiryukhin over 14 years ago in reply to Gang Hua

Expert 2800 points

It is clear now about the PACK8IN with A-law disabled.

However, if I enable the A-law, then according to Figure 34 on page 56 the shift module is bypassed. Thus, if A-law is enabled, then changing CFG.DATASFT register shall not change the values of the data to be processed by IPIPE. Is that correct?

0 Gang Hua over 14 years ago in reply to Gennadiy Kiryukhin

TI__Guru 59300 points

No, CFG.DATASFT shall have no effect on the data flow.

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PACK8 on IPIPE input