Difference between revisions of "DSP"

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(Add unknown fields)
(Provide some DMA examples and more documentation (wip))
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** 3 = ?
 
** 3 = ?
  
−
* Unknown (Bit-offset 4; 1-bit).
+
* Buffer offset writeback (Bit-offset 4; 1-bit).
−
** 0 = ?
+
** 0 = Don't update buffer offset (Word 4)
−
** 1 = ?
+
** 1 = Update buffer offset (Word 4); this respects address wrapping of circular buffers
  
 
* Buffer (Bit-offset 5; 4-bits).
 
* Buffer (Bit-offset 5; 4-bits).
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** 0xC
 
** 0xC
 
** 0xD
 
** 0xD
−
** 0xE = Circular
+
** 0xE = Scratch-Circular
−
** 0xF
+
** 0xF = Scratch
  
 
* Unknown (Bit-offset 9; 1-bit).
 
* Unknown (Bit-offset 9; 1-bit).
Line 101: Line 101:
  
 
* Sample format (Bit-offset 10; 3-bits).
 
* Sample format (Bit-offset 10; 3-bits).
−
** 0x0 = 7 bit (all values are OR'd with 0x80)
+
** 0x0 = 8 bit (1 DSP word / 1 byte); ''sample-count must be multiple of 4, or transfer is skipped; rounded; byte MSB is flipped''
−
** 0x1 = 16 bit
+
*** Buffer to DSP: bytes 0x12,0x34,0x56,0x78 are written to words 0x920000, 0xB40000, 0xD60000, 0xF80000
−
** 0x2 = 24 bit in MSB
+
*** Buffer to DSP: bytes 0x92,0xB4,0xD6,0xF8 are written to words 0x120000, 0x340000, 0x560000, 0x780000
−
** 0x3 = 32 bit (2 words per value: first word receives 24 bit, the next word only 8 bit)
+
*** DSP to buffer: words 0x927FFF, 0xB47FFF, 0xD67FFF, 0xF87FFF are written to bytes: 0x12,0x34,0x56,0x78 ''(Rounded down)''
 +
*** DSP to buffer: words 0x928000, 0xB48000, 0xD68000, 0xF88000 are written to bytes: 0x13,0x35,0x57,0x79 ''(Rounded up)''
 +
** 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 are written to word: 0x123400
 +
*** DSP to buffer: DSP word 0x12347F is written to bytes: 0x34,0x12 ''(Truncated)''
 +
*** DSP to buffer: DSP word 0x123480 is written to bytes: 0x34,0x12 ''(Truncated)''
 +
** 0x2 = 24 bit in MSB (1 DSP word / 4 bytes)
 +
*** Buffer to DSP: bytes 0x00,0x56,0x34,0x12 are written to {{FIXME}}
 +
*** DSP to buffer: word 0x123456 is written to bytes: 0x00,0x56,0x34,0x12
 +
** 0x3 = 32 bit (2 DSP words / 4 bytes)
 +
*** Buffer to DSP: bytes 0x12,0xBC,0x9A,0x78 are written to {{FIXME}}
 +
*** DSP to buffer: words 0x123456, 0x789ABC are written to bytes: 0x12,0xBC,0x9A,0x78
 
** 0x4 = ''Transfer skipped''
 
** 0x4 = ''Transfer skipped''
 
** 0x5 = ''Transfer skipped''
 
** 0x5 = ''Transfer skipped''
−
** 0x6 = 24 bit in LSB
+
** 0x6 = 24 bit in LSB (1 DSP word / 4 bytes)
 +
*** Buffer to DSP: bytes 0x56,0x34,0x12,0x00 are written to {{FIXME}}
 +
*** DSP to buffer: word 0x123456 is written to bytes: 0x56,0x34,0x12,0x00
 
** 0x7 = ''Transfer skipped''
 
** 0x7 = ''Transfer skipped''
  
Line 114: Line 127:
 
** 1 = ?
 
** 1 = ?
  
−
* Step size (Bit-offset 14; unknown size).
+
* DSP address step size (Bit-offset 14; unknown size).
−
** 0 = Keeps reading from same source offset
+
** Each DSP word is addressed using <code>dsp_address + sample_index * step_size</code>
−
** 1 = Reads every sample
 
−
** 2 = Reads every second sample
 
−
** ...
 
  
 
|-
 
|-
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|-
 
|-
 
! 5
 
! 5
−
| Buffer base || The start of the buffer.
+
| Buffer base || ''Only used for circular buffers, ignored otherwise.''{{FIXME|reason=Assumption; it happens for buffer 0xE, but not for buffer 0xF}}
 +
The start of the buffer.
 
|-
 
|-
 
! 6
 
! 6
−
| Buffer limit || The end of the buffer. For 0x1000 bytes, this has to be 0xFFF.{{FIXME|reason=Is this independent of the base?}}
+
| Buffer size || ''Only used for circular buffers, ignored otherwise.''{{FIXME|reason=Assumption; it happens for buffer 0xE, but not for buffer 0xF}}
 +
Size of buffer minus 1. For a buffer with 0x1000 bytes, this has to be 0xFFF.
 
|}
 
|}
  

Revision as of 06:25, 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).
    • 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 are written to words 0x920000, 0xB40000, 0xD60000, 0xF80000
      • Buffer to DSP: bytes 0x92,0xB4,0xD6,0xF8 are written to words 0x120000, 0x340000, 0x560000, 0x780000
      • DSP to buffer: words 0x927FFF, 0xB47FFF, 0xD67FFF, 0xF87FFF are written to bytes: 0x12,0x34,0x56,0x78 (Rounded down)
      • DSP to buffer: words 0x928000, 0xB48000, 0xD68000, 0xF88000 are written to bytes: 0x13,0x35,0x57,0x79 (Rounded up)
    • 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 are written to word: 0x123400
      • DSP to buffer: DSP word 0x12347F is written to bytes: 0x34,0x12 (Truncated)
      • DSP to buffer: DSP word 0x123480 is written to bytes: 0x34,0x12 (Truncated)
    • 0x2 = 24 bit in MSB (1 DSP word / 4 bytes)
      • Buffer to DSP: bytes 0x00,0x56,0x34,0x12 are written to [FIXME]
      • DSP to buffer: word 0x123456 is written to bytes: 0x00,0x56,0x34,0x12
    • 0x3 = 32 bit (2 DSP words / 4 bytes)
      • Buffer to DSP: bytes 0x12,0xBC,0x9A,0x78 are written to [FIXME]
      • DSP to buffer: words 0x123456, 0x789ABC are written to bytes: 0x12,0xBC,0x9A,0x78
    • 0x4 = Transfer skipped
    • 0x5 = Transfer skipped
    • 0x6 = 24 bit in LSB (1 DSP word / 4 bytes)
      • Buffer to DSP: bytes 0x56,0x34,0x12,0x00 are written to [FIXME]
      • DSP to buffer: word 0x123456 is written to bytes: 0x56,0x34,0x12,0x00
    • 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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