Difference between revisions of "DSP"

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(Finish work on DMA examples)
(Add example for saturation)
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*** DSP to buffer: words: <code>0x927FFF, 0xB47FFF, 0xD67FFF, 0xF87FFF</code> &rarr; bytes: <code>0x12,0x34,0x56,0x78</code> ''(Rounded down)''
 
*** DSP to buffer: words: <code>0x927FFF, 0xB47FFF, 0xD67FFF, 0xF87FFF</code> &rarr; bytes: <code>0x12,0x34,0x56,0x78</code> ''(Rounded down)''
 
*** DSP to buffer: words: <code>0x928000, 0xB48000, 0xD68000, 0xF88000</code> &rarr; bytes: <code>0x13,0x35,0x57,0x79</code> ''(Rounded up)''
 
*** DSP to buffer: words: <code>0x928000, 0xB48000, 0xD68000, 0xF88000</code> &rarr; bytes: <code>0x13,0x35,0x57,0x79</code> ''(Rounded up)''
 +
*** DSP to buffer: words: <code>0x800000, 0x7E7FFF, 0x7E8000, 0x7FFFFF</code> &rarr; bytes: <code>0x00,0xFE,0xFF,0xFF</code> ''(Saturated)''
 
** 0x1 = 16 bit (1 DSP word / 2 bytes) ''sample-count must be multiple of 2, or transfer is skipped; truncated''
 
** 0x1 = 16 bit (1 DSP word / 2 bytes) ''sample-count must be multiple of 2, or transfer is skipped; truncated''
 
*** Buffer to DSP: bytes: <code>0x34,0x12</code> &rarr; word: <code>0x123400</code>
 
*** Buffer to DSP: bytes: <code>0x34,0x12</code> &rarr; word: <code>0x123400</code>

Revision as of 07:13, 27 December 2018

The DSPs in the APU are probably "Parthus MediaStream" DSP core (DSP24210/DSP2420?).

Those are similar to Motorola DSP56362 (DSP56300 Family). If so, the datasheet can be found at http://www.nxp.com/docs/en/data-sheet/DSP56362.pdf (Also see "Documentation" section in said datasheet for the related documentation)

Memory Size

Program RAM Size X Data RAM Size Y Data RAM Size MIXBUF Size
GP 4096 x 24-bit 4096 x 24-bit 2048 x 24-bit 992[FIXME] x 24-bit
EP 4096 x 24-bit 3072 x 24-bit 256 x 24-bit n/a

MIXBUF is accessible at X:$001400 in the GP.

Other datasheets for similar DSPs suggest that the memory sizes might be different if instruction cache or switch mode are toggled. It is currently unknown if the DSPs in the Xbox APU support a similar feature[FIXME].

DMA

This section is very incomplete and not much was tested on hardware either

DMA is controlled using peripheral registers:

  • 0xFFFFD4: Memory address of next command block
  • 0xFFFFD5: DMA_START_BLOCK[FIXME]
  • 0xFFFFD6: DMA_CONTROL[FIXME]
  • 0xFFFFD7: DMA_CONFIGURATION[FIXME]

Additionally, bit 7 in the interrupt register at 0xFFFFC5 is set if a DMA End-Of-List has been encountered.

Command blocks

DSP command blocks are loaded from X-Memory.

Word Meaning Notes
0 Next command block address Memory address of next command block.

Bit 14 is used as End-Of-List marker.

1 Transfer control word Controls the DMA transfer:
  • Unknown (Bit-offset 0; 1-bit).
    • 0 = ?
    • 1 = ?
  • Direction (Bit-offset 1; 1-bit).
    • 0 = Buffer to DSP
    • 1 = DSP to buffer
  • Unknown (Bit-offset 2; 2-bit).
    • 0 = ?
    • 1 = ?
    • 2 = ?
    • 3 = ?
  • Buffer offset writeback (Bit-offset 4; 1-bit).
    • 0 = Don't update buffer offset (Word 4)
    • 1 = Update buffer offset (Word 4); this respects address wrapping of circular buffers
  • Buffer (Bit-offset 5; 4-bits).
    • 0x0 = FIFO0
    • 0x1 = FIFO1
    • 0x2 = FIFO2[citation needed]
    • 0x3 = FIFO3[citation needed]
    • 0x4
    • 0x5
    • 0x6
    • 0x7
    • 0x8
    • 0x9
    • 0xA
    • 0xB
    • 0xC
    • 0xD
    • 0xE = Scratch-Circular
    • 0xF = Scratch
  • Unknown (Bit-offset 9; 1-bit).
    • 0 = ?
    • 1 = ?
  • Sample format (Bit-offset 10; 3-bits).[FIXME]
    • 0x0 = 8 bit (1 DSP word / 1 byte); sample-count must be multiple of 4, or transfer is skipped; rounded; byte MSB is flipped
      • Buffer to DSP: bytes: 0x12,0x34,0x56,0x78 → words: 0x920000, 0xB40000, 0xD60000, 0xF80000
      • Buffer to DSP: bytes: 0x92,0xB4,0xD6,0xF8 → words: 0x120000, 0x340000, 0x560000, 0x780000
      • DSP to buffer: words: 0x927FFF, 0xB47FFF, 0xD67FFF, 0xF87FFF → bytes: 0x12,0x34,0x56,0x78 (Rounded down)
      • DSP to buffer: words: 0x928000, 0xB48000, 0xD68000, 0xF88000 → bytes: 0x13,0x35,0x57,0x79 (Rounded up)
      • DSP to buffer: words: 0x800000, 0x7E7FFF, 0x7E8000, 0x7FFFFF → bytes: 0x00,0xFE,0xFF,0xFF (Saturated)
    • 0x1 = 16 bit (1 DSP word / 2 bytes) sample-count must be multiple of 2, or transfer is skipped; truncated
      • Buffer to DSP: bytes: 0x34,0x12 → word: 0x123400
      • DSP to buffer: word: 0x1234FF → bytes: 0x34,0x12 (Truncated)
      • DSP to buffer: word: 0x123400 → bytes: 0x34,0x12 (Truncated)
    • 0x2 = 24 bit in MSB (1 DSP word / 4 bytes); padded
      • Buffer to DSP: bytes: 0x00,0x56,0x34,0x12 → word: 0x123456 (Padding ignored)
      • Buffer to DSP: bytes: 0xFF,0x56,0x34,0x12 → word: 0x123456 (Padding ignored)
      • DSP to buffer: word: 0x123456 → bytes: 0x00,0x56,0x34,0x12 (Zero padding)
    • 0x3 = 32 bit (2 DSP words / 4 bytes); trunacted
      • Buffer to DSP: bytes: 0x12,0xBC,0x9A,0x78 → words: 0x120000, 0x789ABC
      • DSP to buffer: words: 0x12FFFF, 0x789ABC → bytes: 0x12,0xBC,0x9A,0x78 (Truncated)
      • DSP to buffer: words: 0x120000, 0x789ABC → bytes: 0x12,0xBC,0x9A,0x78 (Truncated)
    • 0x4 = Transfer skipped
    • 0x5 = Transfer skipped
    • 0x6 = 24 bit in LSB (1 DSP word / 4 bytes); padded
      • Buffer to DSP: bytes: 0x56,0x34,0x12,0x00 → word: 0x123456 (Padding ignored)
      • Buffer to DSP: bytes: 0x56,0x34,0x12,0xFF → word: 0x123456 (Padding ignored)
      • DSP to buffer: word: 0x123456 → bytes: 0x56,0x34,0x12,0x00 (Zero padding)
    • 0x7 = Transfer skipped
  • Unknown (Bit-offset 13; 1-bit).
    • 0 = ?
    • 1 = ?
  • DSP address step size (Bit-offset 14; unknown size).
    • Each DSP word is addressed using dsp_address + sample_index * step_size
2 Transfer sample count The number of samples to transfer.
3 DSP address This is the address in the DSP:
  • 0x0000 - 0x17FF = X-Memory
  • 0x1800 - 0x27FF = Y-Memory
  • 0x2800 - 0x37FF = P-Memory
4 Buffer offset This is the address within the buffer where the first sample is accessed.
5 Buffer base Only used for circular buffers, ignored otherwise.[FIXME]

The start of the buffer.

6 Buffer size Only used for circular buffers, ignored otherwise.[FIXME]

Size of buffer minus 1. For a buffer with 0x1000 bytes, this has to be 0xFFF.

Related links

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