Support and General Use > Hardware
IPOD (ALL MODELS) iFlash Adapter Issues [SOLVED!?]
rockbox_dev123:
I finally decided to revisit using an SD card in an iPod.
I have:
- iPod 5.5th gen (aka ipodvideo 80GB with 64 MB of RAM).
- The latest hardware revision of the iFlash Solo.
- SanDisk Extreme PRO UHS-I Card - 512GB (SKU: SDSDXXD-512G-GN4IN) (ordered directly from Western Digital to avoid the risk of fakes).
A speed test (writing and reading from /dev/zero with dd) was done using the Apple firmware:
1 GB write = 9.07 MB/s
1 GB read = 12.59 MB/s
Can anyone with the same hardware confirm if they get similar speeds?
The card has the usual bullshit of "200 MB/s" written on it but the "10" on it means that there is only a guaranteed write speed of "10 MB/s". My tests seem to show that it can't achieve this.
bahus:
--- Quote from: rockbox_dev123 on October 04, 2023, 12:08:56 PM ---The card has the usual bullshit of "200 MB/s" written on it
--- End quote ---
It's in megabits(should really be marked as Mb/s). Using SD-reader you should get close to specification speed (200 Mb/s = 25 MB/s)
vitt13:
--- Quote from: bahus on October 04, 2023, 12:40:22 PM ---It's in megabits
--- End quote ---
No, it's actually in megabytes for this specific SanDisk card but it's reading speed, up to 200MB/s. And the writing speed depends on capacity: for 512GB card the writing speed is up to 140MB/s (according to WesternDigital website).
But those speeds are achieved with SDIO 3.0 support on endpoint device.
amachronic:
Bear in mind no matter what card you put inside the adapter you are limited by the iPod's hardware. The first limitation is the CE-ATA bus to connect the drive, which hardware-wise is identical to an SD/MMC bus. I don't know the details for the iPod, but it will be capped to either 25 MB/sec or 50 MB/sec. The second limitation is USB 2.0 -- the maximum speed you can get is roughly 40 MB/sec.
You can probably blame the rest on software and the USB mass storage protocol. Classic USBMS doesn't support queuing requests, which means either the USB bus or the drive will sit idle for around half the time (and thus you lose half the potential transfer speed - you might top out around 25-30 MB/sec). The newer UASP transfer protocol fixes that issue, but it won't be supported by the iPod's firmware.
I've also found that SD cards require large, contiguous writes to get good speeds, like 512KB - 2MB. USBMS can only transfer up to 120 KB at a time, which won't be anywhere near enough to max out the SD card. The only way to work around this issue is (good) caching in the iPod firmware or the iFlash, or again switching to UASP (which supports larger transfer sizes).
So your speeds look rather typical to me for a USB 2.0 device with a typical less-than-stellar caching implementation.
speachy:
--- Quote from: amachronic on October 04, 2023, 03:32:36 PM ---Bear in mind no matter what card you put inside the adapter you are limited by the iPod's hardware. The first limitation is the CE-ATA bus to connect the drive, which hardware-wise is identical to an SD/MMC bus. I don't know the details for the iPod, but it will be capped to either 25 MB/sec or 50 MB/sec. The second limitation is USB 2.0 -- the maximum speed you can get is roughly 40 MB/sec.
--- End quote ---
Just to be pedantic, they're using an iPod 5.5, which has a regular parallel ATA interface that (IIRC) maxes out at UDMA66 burst speeds. Then there's the iFlash PATA/CF<->SD adapter which is its own bottleneck (and I don't think goes over UDMA/33).
--- Quote from: amachronic on October 04, 2023, 03:32:36 PM ---So your speeds look rather typical to me for a USB 2.0 device with a typical less-than-stellar caching implementation.
--- End quote ---
Yeah, those transfer speeds actually better than I'd have expected to see.
Rockbox has a disk performance benchmark that would demonstrate the best we can pull off without the USB interface being a factor. But at the end of the day the iPod SoC simply isn't designed around rapidly shovelling around large amounts of data. And neither is Rockbox.
Anyway; the point of using the SD mods isn't raw transfer performance, it's storage capacity (and to a lesser extent, physical robustness and battery life)
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