hardware

Please tell me about the hardware configuration of the sound-related part of Sega Saturn.

Q)

Please tell me about the hardware configuration of the sound-related part of Sega Saturn.

A)

In Sega Saturn hardware, 68EC000 (CPU), SCSP, and sound memory (512KB RAM) are deeply involved in sound.
The tone data, DSP program, sequence data, and sound driver are all stored in this 512KByte sound memory.
Of these, 44KB (0B000H) is used for the sound driver and its work area.

Is it true that the sound CPU does not have byte access?

Q)

SCSP User's Manual (1st Edition) ● Sound CPU specifications

"Hardware configuration: MC68000 CPU with MC6800 (8-bit) interface removed"

But what does this mean?
Does that mean the sound CPU doesn't have byte access to memory?

A)

The description in the SCSP User's Manual only explains that 8-bit circuits cannot be used due to the hardware design, so there is no need to worry about it when building software.

Of course, the sound CPU can byte-access the sound memory with the "move.b" command.
However, there are "RESET" and "TAS" instructions as instructions for prohibiting use.

reference

For details, refer to Developer's Information STN-51 "Prohibition Order on 68000".

What is "SCSP operates with 22.68 μsec as a whole as one big cycle"?

Q)

In Chapter 4 "Using the SCSP Register / FM Sound Source Method" of the SCSP User's Manual

"SCSP operates as a whole with 22.68 μsec as one big cycle."

Could you please explain this cycle more concretely?

A)

Since SCSP is a system with a sampling rate of 44.1KHz, the time required for one process is within the maximum time allowed for that system.

Since it is processed 44100 times per second, if the reciprocal (= 1/44100 SEC) is taken, the processing must be completed within 22.6757 μSEC.

The same applies to the DSP with built-in SCSP. Since the DSP of SCSP operates in 128 steps, the processing of 128 steps can be completed in 22.6757 μSEC.
Therefore, one step takes (22.6757 ÷ 128 = 0.177154) 177nSEC.

In addition, access from the sound CPU and main CPU is also executed according to the processing time of one step of this DSP, that is, 177ns.