Re: 1 euro Olimex RISC-V mini-PC: this needs Forth ;)

Paul Rubin <no.email@nospam.invalid> wrote:

https://www.hackster.io/news/olimex-s-one-euro-rvpc-single-board-computer-goes-up-for-sale-next-week-1cfe4fe2c985
 
- CH32V003 MCU, 24 MHz, 16KB flash, 2KB ram, and 128B NVRAM

                  ^^^^^^
My datasheet for CH32V003 says 48MHz.

- Uses EC subset of RV32 architecture, so only 16 registers instead
  of 32, but this is fine for Forth
- PS/2 keyboard connector
- VGA video connector
- Can apparenty supposedly 800x600 pixels on VGA, not sure how that is
  possible with just 2K of ram

As noticed it is enough to use buffer for a single scanline.  IIUC
DMA channel + SPI peripherial allow sending pixels at half CPU
clock in parallel with normal CPU work (there will be some slowdown
due to bus cycles "stolen" by DMA).  With 24MHz CPU clock one would
get 12MHz pixel clock which is IMO too slow for 800x600 resolution.
But with 48MHz CPU clock one gets 24MHz pixel clock which is
bordeline of usable.  Of course, with single scanline the scanline
must be filled during horizontal retrace, which may be challenging.
AFAICS this would give about 300-400 clocks which is tight.  Using
two scanlines, one which is displayed and second one filled by CPU,
it is possible to do some graphics like sprites.

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                              Waldek Hebisch