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Further question on loading lm48901 coefficient memory from dat2tab table

Ron Sturtevant
Intellectual 290 points

I am loading the coefficient memory over I2C just fine, but I would like confirmation on the byte order of the load.

I am using the table generated from the tool Royce provided me; the table is of four-byte values:

#define LM48901_TAB_LEN  0x500
const unsigned long lm48901Table0[LM48901_TAB_LEN] = {
  0x002effc4,
         ...

looking at the first value as an example, would the register be loaded over I2C as

<dev_addr> 00 00      00 2e ff c4      (usual 7-byte I2C write packet)

OR

<dev_addr> 00 00      c4 ff 2e 00

There's no byte order info in the file generated by Dat2Tab, and not much documented info about the coefficient memory, either.

Again, any input is appreciated.

Ron Sturtevant

  • 0
    TI__Expert 3840 points

    Hi Ron,

    Royce should be getting back to you tomorrow; he was out today.

    Best Regards,

    JD

  • 0
    TI__Expert 3350 points

    Ron,

    I believe its the same format as the data order into the device, 7:0, 15:8, 23:16, 31:24. Let me confirm with the software guys.

    Regards,

    royce

  • 0 in reply to Royce Higashi
    Intellectual 290 points

    Royce,

    I think the data order is the same as the control registers as well; but how it was stored in the table generated from dat2tab is what I'm unsure of.  Looking forward to an answer tomorrow.

    Ron

  • 0 in reply to Ron Sturtevant
    TI__Expert 3350 points

    Ron,

    Turns out the Dat2Tab format is reversed.  Its 31:24 23:16 15:8 7:0. 

    Regards,

    royce

  • 0 in reply to Royce Higashi
    Intellectual 290 points

    Royce,

    Thanks for the reply.  We figured out, through testing, the byte order  we needed to send to the lm48901. 

    given that the registers are loaded   7:0  15:8  23:16  31:24, it actually works out well that the Stellaris uses little-endian format, since the LSB of the unsigned long is pointed to first when I assign a char pointer to the array element.

    So,

    unsigned char *pData;

    pData = (unsigned char *) &lm48901Table[i];      // example:  0x002effc4

    reg.data7_0[0] = *pData++;           // loads 0xc4

    reg.data15_8[1] = *pData++;          // loads 0xff

    reg.data23_16[2] = *pData++;          // loads 0x2e

    reg.data31_24[3] = *pData;              // loads 0x00

    works great. At least I think so, as when I switch the chip to spatial mode, I get recognizable sound from the chip.  I would assume incorrectly loaded coefficients would greatly distort the audio.

    As a suggestion, it would simplify things for others dealing with big vs little endian issues if a modified Dat2Tab stored the coefficient values as unsigned char, four bytes per line, with markers in the comments (something like this):

    unsigned char lm48901Coefficient[0x500] = {

    // 7:0    15:8     23:16   31:24

    0xc4,    0xff,       0x2e,    0x00,

    etc, etc, etc.