hardware

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

Q)

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

A)

In the Sega Saturn's hardware, the 68EC000 (CPU), SCSP, and sound memory (512KB RAM) are deeply involved in sound.
All tone data, DSP programs, sequence data, and sound drivers will be stored in this 512KByte sound memory.
Of this, 44KB (0B000H) is used for the sound driver and its work area.

Is it true that the sound CPU cannot access bytes?

Q)

Sound CPU specifications in SCSP User's Manual (1st edition)

"Hardware configuration: MC68000CPU with MC6800 (8-bit) interface removed"

But what does this mean?
Does this mean that the sound CPU cannot access byte memory?

A)

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 be concerned about this when building software.

Of course, the sound CPU can access the sound memory byte by using the "move.b" command.
However, there are "RESET" and "TAS" commands that are prohibited from use.

reference

For more information, please refer to Developer's Information STN-51 "68000 Prohibition Order".

What does "SCSP operates as one large cycle of 22.68μsec" mean?

Q)

SCSP User's Manual Chapter 4 " When using the SCSP register/FM sound source method "

"SCSP operates as one large cycle of 22.68μsec"

However, could you please explain this cycle more specifically?

A)

SCSP is a system with a sampling rate of 44.1KHz, so the time required for one processing is within the maximum time allowed by the system.

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

The same is true for DSPs with built-in SCSPs; SCSP DSPs operate in 128 steps, so processing for 128 steps can be completed in 22.6757μSEC.
Therefore, one step takes (22.6757÷128=0.177154)177nSEC.

Also, accesses from the sound CPU and main CPU are executed in accordance with the processing time for one step of this DSP, which is 177ns.