[Coco] Gotek floppy emulator

[Steven Hirsch]

On Sun, 14 Feb 2016, Bill Pierce via Coco wrote:

> Frank, I see a problem right off with this unit...

> It uses 1.44meg HD, 512 byte sectors at 500kbps...

> The Coco uses 720k DD, 256 byte sectors...

> There's no mention of being able to set the unit for the older 720k 
> drives. IIRC, even on the real drives of that type, you had to modify 
> them physically to make them work if they did not have jumpers. I doubt 
> this usit could be modified in that way.

> It's the very reason we can't use the real drives on the "newer" 
> computers to read/write coco disks. The controller chipset was different 
> for those drives and no longer supported 720k or 256 byte sectors.

> If there's a 720k version of this, then GREAT!
>
> Looking a little further on that site, I found this:
>
> http://www.newegg.com/Product/Product.aspx?Item=9SIA3XT1DB1480&cm_re=usb_floppy_drive_emulator-_-9SIA3XT1DB1480-_-Product
>
> It says "72k" but reading the specs, it says "720k" (typo?). This seems 
> to be more what's needed :-)
>
> All the rest on NewEgg seem to be 1.44 meg units.

All legitimate concerns.  That's why you reflash the unit with HxC 
firmware:

http://hxc2001.com/download/floppy_drive_emulator/index.html

and prepare yourself for an educational experience.

Search for "USB Stick STM32 HxC Floppy Emulator".  Jeff has ported the 
logic from the more expensive HxC hardware product to the Gotek device. 
He sells the firmware upgrade for 10-euros per unit, which is quite 
reasonable.  All other support software is free for the download.

You need a USB-parallel interface and access to a Windows box to reflash 
the firmware.  The interface is a $10 problem from Adafruit - maybe even 
cheaper on eBay.  I've done two units so far and it's painless.

The HxC utility software supports conversion from many image formats to 
and from the HFE format used by the emulator.  Some experimentation may be 
required to get it working on the target system and not all controllers 
and drivers are compatible.  But, at this price it's worth a try.

I can tell you from hard experience that the USB stick is a critical 
aspect. The Sandisk Extreme is about 10-20x faster on small block RW 
operations than the average thumb drive and this is critical to getting 
some vintage systems to cooperate.  The operational buffer on the emulator 
cannot hold the entire image, so he suspends index pulses for a short time 
on track change to write back modified tracks and read the new target 
track.  This latency can cause problems with some diskette controllers 
and/or device drivers.  For example, almost any USB stick will work with a 
PC clone, but my Heath H89 did not cooperate until I moved to the Sandisk 
drive and recoded the device drive to introduce more head-settle time 
after track change.

ALL of the Gotek drives with 3-digit LCD display are identical at the 
hardware level, regardless of case color or whatever else the vendor says 
about it and they all behave the same way when re-flashed.  Some of the 
eBay vendors have them as low as $18.  Warning:  A few of the vendors 
claim to ship from US locations.  They're all liars.  If the price is down 
around $18-25, you can guarantee it's coming on a slow boat from China 
with 2-4 week delivery time.  If you want one quickly, be prepared to pay 
$35-40 from Amazon.

Steve


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