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ubb-jtag/README: ideas for increasing the speed

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Werner Almesberger 2013-01-04 15:41:34 -03:00
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ubb-jtag/README
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@ -167,6 +167,7 @@ ben# jtag
jtag> cable gpio tdi=107 tdo=105 tck=109 tms=108 jtag> cable gpio tdi=107 tdo=105 tck=109 tms=108
jtag> detect jtag> detect
For the next step, we need fjmem.bit, e.g., available here: For the next step, we need fjmem.bit, e.g., available here:
http://milkymist.org/updates/fjmem.bit.bz2 http://milkymist.org/updates/fjmem.bit.bz2
@ -188,3 +189,21 @@ jtag> detectflash 0
Since the sysfs GPIO interface is rather slow and we make things Since the sysfs GPIO interface is rather slow and we make things
worse by swapping to compressed RAM, the loading of fjmem.bit worse by swapping to compressed RAM, the loading of fjmem.bit
takes about four or five minutes. takes about four or five minutes.
Going faster
------------
In many applications, UrJTAG will be able to run without compressed
swap and thus faster. Smaller amounts of data will also make even
slow transfers more bearable.
To further increase the speed, a Ben-specific GPIO driver could be
written that accesses registers directly without the very long
detour through sysfs.
Finally, even higher speeds could be reached by using the MMC
controller to send data, similar to UBB-VGA. For this purpose, CMD
and DAT0 have been left unconnected. When connecting them to each
other, they could be used to generate fake start bits, signaling
the MMC controller to begin a transfer. (See ubb-vga for details.)