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N64 Data Access Rates

 
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zoinkity
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Joined: 24 Nov 2005
Posts: 1683

 PostPosted: Fri Mar 31, 2023 9:35 am    Post subject: N64 Data Access Rates Reply with quote Back to top

If you've ever been interested in how quickly an N64 / 64DD / iQue can read data different ways, then you might be interested in this:
http://www.bwass.org/bucket/access_rates.7z

These are a series of screenshots of a clocker, testing different hardware access rates on a console. The original purpose was to come up with a workaround for softpatching translations onto retail disks since DMAs are too fast, causing run conditions. That's why the transfer blocks sizes are a bit odd. The idea is to get real numbers for a real threaded enviroment, even if they're somewhat idealized.

The hardware:
  • 64DD disk
  • N64 maskrom (in this case the IPL which is set a smidge faster than DIPs but whatevs, was close enough to modem results)
  • N64 flashcart
  • iQue in mode 2
  • an invalid address (bad request timeout)

The conditions tested:
  • DMA, in multiple 0x140000 segments
  • IO read using the libultra function; it locks and unlocks the IO queue each word read, checks PI ready, then reads a word
  • "fast" IO, which only twiddles the locks once and loops the ready/read portion
  • Disk read, seek, encode/decode rates


If you don't want to browse the pictures, the results:
Code:
64DD time to read, irregardless of zone: 3779972 uSec

.: DMA avg. bytes/sec :.
maskrom   10653508
64Drive   5271286   
iQue      6537210
invalid   12559214

.: IO avg. bytes/sec :.
maskrom   587088
64Drive   557954
iQue      36515
invalid   732837

.: Fast IO avg. bytes/sec :.
maskrom   1641785
64Drive   1417382
iQue      37928


That's not a mistake. It really does take over a minute and a half to read the first zone one word at a time on an iQue. I thought the program locked ;*) It has to decrypt a whole 0x4000 block at a time; DMAs buffer the decrypted data but individual word reads require redecryption each request.

As you'd expect, it isn't really possible (or sensible) to clock emulators. They'll complete a DMA in only a few dozen uSec so transfer rates are effectively instantaneous.
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MRKane
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Joined: 11 Dec 2008
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 PostPosted: Fri Mar 31, 2023 5:10 pm    Post subject: Reply with quote Back to top

Very cool! Frankly I'm crazy impressed with the progress on the iQue - see I've got this dream where we might one day play GE and PD with silky framerates on actual hardware Wink
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zoinkity
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Joined: 24 Nov 2005
Posts: 1683

 PostPosted: Fri Mar 31, 2023 9:05 pm    Post subject: Reply with quote Back to top

That day is closer than you think ;*)
http://www.shootersforever.com/forums_message_boards/viewtopic.php?t=8236

Hoping the day of aftermarket multiplayer boxes arrives soon. Those are hilariously expensive.


PD will be...awful to say the least, no idea where to stick the save files (eeprom + controller paks all buffered in rdram? Aegh...) but wow, if it's even half what GE pulls down would be worth it.
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