SMPS68k RAM Area

Dear Sonic Retro,

Today I thought it was a good idea to release my findings about the RAM that SMPS occupies when being active. I am going to focus on Sonic 1 here, which means that this might be different for any other game using SMPS.

So, here we go:

SMPS RAM starts at (FF)F000.

Lenght = either B (byte), W (word) or L (long)

Sections:

Code (Text):

1. F030-F05F       PCM
2. F060-F08F       FM1
3. F090-F0BF       FM2
4. F0C0-F0EF       FM3
5. F0F0-F11F       FM4
6. F120-F14F       FM5
7. F150-F17F       FM6
8. F180-F1AF       PSG1
9. F1B0-F1DF       PSG2
10. F1E0-F20F       PSG3/NOISE

SMPS general values:

Code (Text):

1. ADDR. LENGTH  Description
2. F001  B       Timer, counts from 0 up to tempo byte 2 all the time
3. F002  B       Tempo byte 2 from song (See SCHG:Music_Hacking)
4. F008  L       Pointer to where the FM instruments for this song are (in ROM)
5.               (or voices, for you noobs =P)
6. F028  B       Tempo byte 2 from song (See SCHG:Music_Hacking)
7. F214  B       FOR SOME SONGS: Ticks/$F until loop is over

CHANNEL SECTIONS:

Code (Text):

1. 0     L       $00000000
2. 8     L       $00000000
3. 10    B       Channel information byte
4.                 Bit 1      if 1 then Channel is mute
5.                            if 0 then channel is playing
6.                            Note: for PCM, Bit 1 is always 0!
7.                 Bit 7      if 1 then channel is used in song at all
8.                            if 0 then channel is not used in song at all
9. 11    B       Modifier...
10.               Known: For PSG3, if $E0, then the channel is noise, else it is
11.               a melodic PSG channel.
12. 12    W       constant   xx 00 where xx is the first tempo byte of the song  
13. 14    L       Data Position Pointer
14.               = Channel's current position inside ROM
15. 18    W       Channel modifier (From SMPS file; see SCHG:Music_Hacking)
16. 1A    B       ?
17. 1B    B       Current insturment (always 0 for PCM)
18. 1C    B       Current position in PSG Volume envelope (0 for PCM and FM)
19. 1D    B       ???? Always $30 for xm3smps/xm4smps created songs,
20.               SEGA SMPS songs sometimes have $2C here ... Modifying this will
21.               cause illegal instruction error !
22. 1E    B       Ticks until next note is triggered
23.               Note: This also applies for rests!
24.               This also is present at completely unused channels, and counts
25.               upwards in this case! If the song doesn't loop, then it also counts upwards
26.               once the song has ended!
27. 1F    B       Next note descriptor
28.               If bit 4 is set, the next note is a rest (?)
29. 20    B       If PCM is enabled, this is current PCM sample played (2nd byte= 0)
30.       W       Current frequency (FM / PSG)
31.               See Addition #1 below
32. 22    W       Note-playing-but-channel-muted:
33.               Byte 1: amount of ticks channel is silent
34.               Byte 2: $04, if this is currently going on...
35. 24    L       Quote from SCHG:
36.               " Coordination Flag $F8yyyy
37.                 Jump to position yyyy (keep previous position in memory for returning) "
38.  
39.               This longword is the return adress in ROM. $00000000 if unused at the moment
40. 28    W       Effect:
41.               Byte 1: Ticks until effect takes place
42.                       ($00 if no effect in sight)
43.               Byte 2: Type of effect? (I've only experienced modulation so far)
44. 2A    L       Effect data
45.               For modulation:
46.               Byte 1: F9 if frequency gets higher, 07 if frequency gets lower
47.               Byte 2: ?
48.               Word after that: what gets added to frequency (7000 - FFFF = negative !)
49. 2E    B       $00
50. 2F    B       ?? (For PSG: If $E7, then channel is Noise)

If you have any questions, please contact me

Addition #1:
A note in a SMPS song is a byte, starting from $81. Lets assume x is the note.
the xth note inside a frequency table is then pulled and sent to RAM.

Here's a reference for FM:

Code (Text):

1. 025e = (b-0)
2.  
3. 0284 = C-1  0A84 = C-2  1284 = C-3  1A84 = C-4  
4. 02AB = C#1  0AAB = C#2  12AB = C#3  1AAB = C#4  
5. 02D3 = C-1  0AD3 = C-2  12D3 = C-3  1AD3 = C-4  
6. 02FE = D#1  0AFE = D#2  12FE = D#3  1AFE = D#4  
7. 032D = E-1  0B2D = E-2  132D = E-3  1B2D = E-4  
8. 035C = F-1  0B5C = F-2  135C = F-3  1B5C = F-4  
9. 038F = F#1  0B8F = F#2  138F = F#3  1B8F = F#4  
10. 03C5 = G-1  0BC5 = G-2  13C5 = G-3  1BC5 = G-4  
11. 03FF = G#1  0BFF = G#2  13FF = G#3  1BFF = G#4  
12. 043C = A-1  0C3C = A-2  143C = A-3  1C3C = A-4  
13. 047C = A#1  0C7C = A#2  147C = A#3  1C7C = A#4  
14. 0A5E = B-1  125E = B-2  1A5E = B-3  225E = B-4  
15.  
16. 2284 = C-5  2A84 = C-6  3284 = C-7  3A84 = C-8
17. 22AB = C#5  2AAB = C#6  32AB = C#7  3AAB = C#8
18. 22D3 = C-5  2AD3 = C-6  32D3 = C-7  3AD3 = C-8
19. 22FE = D#5  2AFE = D#6  32FE = D#7  3AFE = D#8
20. 232D = E-5  2B2D = E-6  332D = E-7  3B2D = E-8
21. 235C = F-5  2B5C = F-6  335C = F-7  3B5C = F-8
22. 238F = F#5  2B8F = F#6  338F = F#7  3B8F = F#8
23. 23C5 = G-5  2BC5 = G-6  33C5 = G-7  3BC5 = G-8
24. 23FF = G#5  2BFF = G#6  33FF = G#7  3BFF = G#8
25. 243C = A-5  2C3C = A-6  343C = A-7  3C3C = A-8
26. 247C = A#5  2C7C = A#6  347C = A#7  3C7C = A#8
27. 2A5E = B-5  325E = B-6  3A5E = B-7

The table gets pulled from a location in the Play Music routines of SMPS:

Code (Text):

1. word_72790:     dc.w $25E,  $284,  $2AB,  $2D3,  $2FE,  $32D,  $35C,  $38F, $3C5  
2.                 dc.w $3FF,  $43C,  $47C,  $A5E,  $A84,  $AAB,  $AD3,  $AFE, $B2D  
3.                 dc.w $B5C,  $B8F,  $BC5,  $BFF,  $C3C,  $C7C,  $125E, $1284      
4.                 dc.w $12AB, $12D3, $12FE, $132D, $135C, $138F, $13C5, $13FF
5.                 dc.w $143C, $147C, $1A5E, $1A84, $1AAB, $1AD3, $1AFE, $1B2D
6.                 dc.w $1B5C, $1B8F, $1BC5, $1BFF, $1C3C, $1C7C, $225E, $2284
7.                 dc.w $22AB, $22D3, $22FE, $232D, $235C, $238F, $23C5, $23FF
8.                 dc.w $243C, $247C, $2A5E, $2A84, $2AAB, $2AD3, $2AFE, $2B2D
9.                 dc.w $2B5C, $2B8F, $2BC5, $2BFF, $2C3C, $2C7C, $325E, $3284
10.                 dc.w $32AB, $32D3, $32FE, $332D, $335C, $338F, $33C5, $33FF
11.                 dc.w $343C, $347C, $3A5E, $3A84, $3AAB, $3AD3, $3AFE, $3B2D
12.                 dc.w $3B5C, $3B8F, $3BC5, $3BFF, $3C3C, $3C7C

for PSG the order is reverse; the lower the value, the higher the sound:

Code (Text):

1. word_729CE:     dc.w $356, $326, $2F9, $2CE, $2A5, $280, $25C, $23A, $21A
2.                 dc.w $1FB, $1DF, $1C4, $1AB, $193, $17D, $167, $153, $140
3.                 dc.w $12E, $11D, $10D, $FE, $EF, $E2, $D6, $C9, $BE, $B4
4.                 dc.w $A9, $A0, $97, $8F, $87, $7F, $78, $71, $6B, $65    
5.                 dc.w $5F, $5A, $55, $50, $4B, $47, $43, $40, $3C, $39    
6.                 dc.w $36, $33, $30, $2D, $2B, $28, $26, $24, $22, $20    
7.                 dc.w $1F, $1D, $1B, $1A, $18, $17, $16, $15, $13, $12    
8.                 dc.w $11, 0

 

http://forums.sonicretro.org/index.php?showtopic=20667 ?

 

Okay. Sorry.

 

No, the sections have 16 $00 bytes before that.

EDIT: Oh, thats what you mean, I accidentally something wrong... Fixed, see 1st post again.

 

Hmmm. What is the last byte for then? For PSG3 I see that it is $E7 some times :S all the other times it is just $00 :/

And thanks for the information, I will incorporate it into the 1st post later

 

Nice to see that people are eager to complete the list. As soon as I get time, I will incorporate it into the first post.

By the way, I might also, depends on how busy the day will be, add this to SCHG:Music_Hacking.

Cheers.