Genos internal memory: A speculation

First, you have to get the mule’s attention.

Yamaha Genos™ hasn’t hit the streets yet and here is a speculative article about its hardware design…

I’d like to thank Kari V., Mihai and Joe H. on the PSR Tutorial Forum for getting this mule’s attention. They deserve the credit.

Spex

Here are a few Genos specifications that drew curious looks:

  • Polyphony: 256 (max.) (128 for Preset Voice + 128 for Expansion Voice)
  • Voice expansion memory: Approximately 1.8GBytes
  • Internal memory: Approximately 58GBytes

Normally, a Tyros has a large hard disk inside for bulk storage. The hard drive contains a file system to hold style files, song files, text files and a whole lot more. The Tyros 5 shipped with a 500GB hard disk drive. Tyros 5 internal memory — some form of non-volatile flash — is spec’ed at approximately 6.7MBytes. Yes, megabytes.

Word from the demonstrations is that the Genos has neither a hard disk drive nor a solid state drive (SSD). Thus, “Internal memory” is not directly user expandable or upgradeable. Eliminating the hard disk drive, the bracket and access door makes good sense because it reduces weight and chassis complexity. SSDs are still a little pricey for a cost-sensitive manufacturer like Yamaha. If it’s not a hard drive and if it’s not an SSD, then what is it?

Next, what’s up with that polyphony spec? 128 voice polyphony when you play preset voices only and 128 voice polyphony when you play a voice from user voice expansion memory? That’s rather unorthodox.

The high-level view

This is where the Yamaha SWP70 tone generator (TG) integrated circuit (IC) comes into the story.

The SWP70 uses ONFI-compatible NAND flash as its waveform memory. “ONFI” is the industry standard Open NAND Flash Interface. ONFI-compatible chips are the same NAND flash used in SSDs. The SWP70 caches the waveform data in a fast SDRAM just like an SSD in order to have fast, random access to samples.

Yamaha have created a tone generator IC that integrates an SSD-like flash and cache controller. This design eliminates the cost and latency of the SATA bus which normally connects an SSD within a PC or Mac.

For the hardware inclined, here’s a short speculative answer. There are two tone generator ICs each having their own ONFI flash memory. One TG and flash memory (call this one “TG A”) handles factory presets. The other TG and flash memory (call this “TG B”) handles user expansion voices.

The “TG B” flash memory is 64GBytes of ONFI NAND flash. Through software, it is partitioned into a file system partition (62GB?) and a user expansion voice partition (2GB).

The file system partition contains the initial factory content (4GB). The remaining space (58GB) is the “Internal memory” quoted in the Genos specifications.

So, Yamaha engineering decided to use space in one of the ONFI flash memories for bulk storage in order to cut the weight and expense of a magnetic hard drive (heavy) or an SSD (lighter than a hard drive, but not cheap).

If this is true — if — then there are some positive implications for the future of Genos. More at another time.

Ingenious, yes. User expandable, no.

Do I know this for sure? Oh, hell no. We need a service manual. Even a visual inspection of the digital logic board (DM) might not be conclusive.

The low-level view

The notional diagram below shows some of the major interfaces to the SWP70. [Click on images to enlarge.]

  • The CPU bus connects the SWP70 to the main control CPU and other major subsystems that require CPU-based data and control.
  • The ABUS allows SWP70s to communicate with each other when more than one SWP70 is in a system.
  • The waveform memory (NAND flash) communicates with the SWP70 over a Open NAND Flash Interface (ONFI) bus. This open industry standard lets Yamaha use commodity flash memory for waveform ROM. Waveform memory is split into upper and lower bytes with shared control signals. This arrangement instantly doubles bus bandwidth versus a single ONFI data channel.
  • The Serial audio bus brings audio data into the SWP70 (e.g., from the ADC) and sends audio data to the DACs and other subsystems.

Then, the fun begins. The SWP70 has three parallel SDRAM memory channels for wave and DSP working memory.

  • The DSP working memory is a large, scratch-pad memory for effect computation. I believe this memory is also the working memory for Montage FM-X.
  • The Wave working memory is a fast, read/write data cache which holds samples after they are read from the waveform memory. Remember, NAND flash favors sequential block mode read access, transferring data on the nibble-serial ONFI bus. The wave working memory plays the same role as the data cache in an SSD storage unit.

Memory capacities vary across products depending upon target polyphony, effect workload and, of course, the sample set.

Here are capacities for the PSR-S770, PSR-S970 and Montage. All capacities are physical (i.e., raw physical storage space).

             AWM     Waveform    Wave     DSP
          Polyphony   Memory   Working  Working
          ---------  --------  -------  -------
PSR-S770     128      512MB      32MB     8MB
PSR-S970     128       2GB       32MB     8MB
Montage      128*      4GB       32MB    16MB
          * Stereo/mono

The Montage DSP working memory is twice as large as the PSR-S970 reflecting the larger number of supported effect units.

The ONFI standard is the same standard used in solid state drives (SSD). Thus, Yamaha can reap the benefit of lower cost commodity flash. The wave working memory caches data just like an SSD. The SWP70 design yields maximum bandwidth to and from NAND flash without the expense or latency of a SATA bus. Thanks to ONFI, Yamaha can increase waveform memory size by dropping in higher capacity ONFI-compatible devices. User waveform (voice) expansion memory resides in these same memory components, so one should expect bigger user expansion memory in the future as well as bigger factory sample sets.

The SWP70 reads and writes two flash memories in tandem effectively sending a 16-bit word on each ONFI bus cycle. (See diagram below.) One memory provides the HIGH byte and the other memory provides the LOW byte. The same ONFI control signals are sent to both. For people who like to trash Yamaha for not using SSD, please note that tandem access doubles the transfer bandwidth over a single ONFI data path solution. (Of course, an SSD could do the same thing.)

I’ll bet that using the ONFI waveform memory for file system access made the tone generation guys nervous. Would file system traffic rob memory bandwidth from the tone generators?

Yamaha know latency. They spend a lot of time, money and intellectual effort understanding latency and conquering it. That’s where the second waveform working memory comes into play. Samples heading to the tone generators could be held in one waveform working memory while file system data could be held in the second, separate working memory. This organization separates the memory traffic and prevents file access from disturbing the critical, must-be-predictible sample stream. When the two channels arbitrate for the ONFI bus, the sample stream feeding tone generation could be given priority.

Copyright © 2017 Paul J. Drongowski