Why VGA and not DVI/HDMI


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lew247

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Joined: 23/12/2015
Location: United Kingdom
Posts: 1584
Posted: 03:25pm 22 Jan 2022      

  Mixtel90 said  The RP2040 has 264KB of RAM. Obviously it's impossible to use anywhere near that as a frame buffer - you need communication routines and routines to handle the frame buffer, together with some workspace for serial buffers etc.

Could we not just use 16mb QSPI ram like other boards do and use some of that?

External Flash is accessed via the QSPI interface using the execute-in-place (XIP) hardware. This allows an external
flash memory to be addressed and accessed by the system as though it were internal memory. Bus reads to a 16MB
memory window starting at 0x10000000 are translated into a serial flash transfer, and the result is returned to the master
that initiated the read. This process is transparent to the master, so a processor can execute code from the external
flash without first copying the code to internal memory, hence "execute in place". An internal cache remembers the
contents of recently-accessed flash locations, which accelerates the average bandwidth and latency of the interface.
Once correctly configured by RP2040's bootrom and the flash second stage, the XIP hardware is largely transparent,
and software can treat flash as a large read-only memory. However, it does provide a number of additional features to
serve more demanding software use case


That to me reads like you can use the QSPI ram and for all intent and purposes it's treated like internel ram?

720P resolution in full colour could produce some stunning graphics
In a few years there won't be many monitors around that still have a vga connector, which is why I first started thinking about this
It's when I wanted my weather display to run on a proper monitor I had to switch to a Pi and when Picromite wasn't able to run on the pi properly because of the stupid broadcom licencing rules that I had to go to python
However the Pico runs mmbasic perfectly it can output 720P video with no issues even with the base 256K ram in place, so surely with a 16mb qspi flash it should work?
Even if picomite or mmbasic wasn't able to handle video, surely the better resolution and the fact it can be displayed on large screens and not just tiny display might make it worthwile investigating?

To answer the previous comment by elk1984 there is no issue with licencing because HDMI would not be output, only DVI which has no licencing issues at all.
And it only needs 8 X 270 Ohm resistors, 8 io pins including the clock ones.
Oh and the software converted to basic

You can download the picodvi-test.zip  and get started playing around with the .UF2 example compiles in it. It also includes a PDF which gives you a step-by-step guide
Edited 2022-01-23 01:26 by lew247