VGA text driver questions/concepts - Q's probably for Chip - vga streamer interrupts wkg

rogloh

There seems to be some small jitter and I can't lock onto the output signal perfectly with my LCD monitor each time I auto adjust and some pixels look a bit wider than others. Are you using fractional ratios of P2:pixel clocks or integer ratios? Fractional ratios could cause this issue.

cgracey

@Cluso99 said:
VGA using Interrupts
Attached is VGA_640x480_text_80x40_interrupt which runs the streamer under interrupts

I found a couple of traps

• waitx does not work in the non-interrupt code - I presume we cannot interrupt a waitx instruction ?
• don't use calls in the interrupt code - I expect/presume we only have one internal stack space

' setint1 #INT_XMT
The INT_xxx definitions (as defined in the spin document 34r/s) appear not to work

You can do CALLs within ISRs. There is as much stack space as was available before the interrupt.

WAITX cannot be interrupted. Better to use loops for timing if interrupts are desired.

Cluso99

There's actually a section I missed inserting "resi1" into (4 places)

OOPS - this breaks the code
found it - it returns in a rep loop - another trap

.line
        xcont   m_bv,#0         'do before-visible part of scan line
        resi1

        rdfast  #0,screen_base      'set fifo to read from current screen row

        rep @.chr,#cols     'ready to output 8 pixels for each chr

        rfbyte  pa      wc  '2  get chr
        bitc    m_px,#16        '2  select colors using msb of chr
        and pa,#$7F         '2  trim chr to 7 bits
        add pa,font_base        '2  add offset for top/middle/bottom lines of chr
        rdlut   pa,pa           '3  look up four lines of chr
        shr pa,font_line        '2  get line of interest into lower 8 bits
        xcont   m_px,pa         '2 =15  output 8 single-bit pixels to streamer
'       resi1                                       <<<<<<<<<<<<< cannot do this within a rep loop!!!
.chr
        xcont   m_bs,#0         'do before-sync part of scan line
        resi1
        xzero   m_sn,#1         'do sync part of scan line
        resi1

I will update the code later

Cluso99

@cgracey said:

@Cluso99 said:
VGA using Interrupts
Attached is VGA_640x480_text_80x40_interrupt which runs the streamer under interrupts

I found a couple of traps

• waitx does not work in the non-interrupt code - I presume we cannot interrupt a waitx instruction ?
• don't use calls in the interrupt code - I expect/presume we only have one internal stack space

' setint1 #INT_XMT
The INT_xxx definitions (as defined in the spin document 34r/s) appear not to work

You can do CALLs within ISRs. There is as much stack space as was available before the interrupt.

WAITX cannot be interrupted. Better to use loops for timing if interrupts are desired.

The places where calls would be dangerous is calling the blanks because you would return while still inside the call so the stack would likely get confused!!

Cluso99

@rogloh said:
There seems to be some small jitter and I can't lock onto the output signal perfectly with my LCD monitor each time I auto adjust and some pixels look a bit wider than others. Are you using fractional ratios of P2:pixel clocks or integer ratios? Fractional ratios could cause this issue.

Fractional

        rdlong  pa,#@clkfreq        'calculate streamer frequency
        qfrac   ##fpix,pa
        getqx   pa
        shr pa,#1
        setxfrq pa

I'm just using 216MHz (optimal for 1280x1024) where 50MHz multiples are better for 640x48.
Can you try with _clkfreq = 200_000_000 ?

At 200MHz: I'm not seeing jitter on my LCD but I am seeing some wider pixels (consistent) on some of the characters. It's a little blurry too. I'm using an Acer 24" 1920x1080.

ozpropdev

WAITX blocks interrupts.

Try
setint1 #EVENT_XMT

rogloh

Yeah that looks cleaner with 200MHz setting Cluso.

Cluso99

Thanks Roger. I think the wider character pixel rows are because of the scaling in my monitor.

Thanks Brian. I'll try EVENT_XMT. Yes I realised why waitx cannot be interrupted but it's a trap because it's easily forgotten. Initially I just went gungho and changed the lot and of course nothing worked. Then I had to start again, implementing bits at a time and testing.

I've realised the rep section is tight timing and so it's likely missing the interrupt and once that happens the whole process stops. I tried a loop before I realised this. But I think the ultimate may be to do the whole line and display it in one go instead of a character at a time.

Cluso99

Here is the code. VGA 640x480 text 80x40

There's a few commented out sections.
Tested on P2-EVAL and RetroBlade2
Specify both VGA-Base (4 pins HBGR) and Vsync (VS) pins seperately
Flashes LEDs on both pins 0 and 56

Forgot to test this - it works so apply the change if you wish

        mov ijmp1,#field        'set up streamer-empty interrupt
'       setint1 #10
        setint1 #EVENT_XMT