connect parallel pins to gpios, data out over usb-serial. i've done this a few times using the very same socket depicted in TFA
Re:Reading Parallel nor Flash with JTAG
by RetroTechie on Monday March 25, 2024 @03:33PM
(#39820412)
Or hook up a counter (reset + clock signal, that's 2 gpio's), and feed counter output to address lines.
If you're really short on gpio's, you could do the same with the data outputs (use some parallel in, serial out shift register, or a multiplexer that selects which data bit(s) to read).
Re:Reading Parallel nor Flash with JTAG
by Boardbricker34 on Monday March 25, 2024 @03:13PM
(#39820210)
Updated. Curious about how you wound up tying all 30+ pins on the pico (26 gpio)
You can put that nor flash into byte mode, saving you 8 data lines in exchange for an extra address line.
You can also throw a shift register in to increase the number of GPIOs.
Re:Reading Parallel nor Flash with JTAG
by Boardbricker34 on Monday March 25, 2024 @04:00PM
(#39820640)
Yes, I suppose this would be a functional way to do this. It would take much longer (double or quadruple depending on data bus size). But none the less, it could work.
I think you'll find that even that is much quicker than twiddling lines via boundary scan. At best, JTAG boundary scan is basically one giant shift register generally hundreds to thousands of bits long. Every cycle you'd need to shift out the whole thing even if you change the state of one signal.
D0-D15
A0-A15
CE (STATIC)
OE (STATIC)
WE (STATIC)
WP (STATIC)
RST (STATIC)
GND (STATIC)
3.3 (STATIC)
The pi would have to request an address over the address bus to the flash chip using A0-A15 and then the data would come over on D0-D15 and you would have to collect it. A pi would work if external static pins were held or tied to their respective state in order to read. TSOP56/48/40 would not work for this as a pico only has 26 GPIO pins available.
Here are images of the busses for both serial and parallel nor flashes. The bus sizes are different. Serial: https://www.embedded.com/wp-content/uploads/contenteetimes-i...
Parallel: https://www.embedded.com/wp-content/uploads/contenteetimes-i...