* [9front] games/gb: various HDMA fixes
@ 2021-02-07 23:22 Michael Forney
0 siblings, 0 replies; only message in thread
From: Michael Forney @ 2021-02-07 23:22 UTC (permalink / raw)
To: 9front
H-blank DMA should only transfer 16 bytes per h-blank, rather than
waiting for the first h-blank and then transferring the whole size.
HDMAC should read 0xff when the transfer is finished, and 0 in the
high bit when the transfer is ongoing. Also, if 0 is written in the
high bit, the current transfer should be aborted.
Introduce two flags, DMAREADY and DMAHBLANK rather than special
constants 1 and -1. If dma is non-zero, there is an ongoing DMA. If
DMAREADY is set, the next chunk is ready to transfer.
Reference: https://gbdev.io/pandocs/#ff55-hdma5-cgb-mode-only-new-dma-length-mode-start
diff 9f73daae4c186334de5c9ee5b6bb0d9aa598f9bd 3fc115a6ff6eef65210fb78a51128958d2b55910
--- a/sys/src/games/gb/dat.h Sat Feb 6 04:50:06 2021
+++ b/sys/src/games/gb/dat.h Sun Feb 7 15:22:39 2021
@@ -8,7 +8,7 @@
extern uchar vram[16384];
extern int nrom, nback, nbackbank;
extern u32int pal[64];
-extern s8int dma;
+extern u8int dma;
extern u32int divclock;
extern Event *elist;
@@ -113,6 +113,9 @@
FEATRAM = 1,
FEATBAT = 2,
FEATTIM = 4,
+
+ DMAREADY = 1,
+ DMAHBLANK = 2,
INIT = -1,
SAVE = -2,
--- a/sys/src/games/gb/gb.c Sat Feb 6 04:50:06 2021
+++ b/sys/src/games/gb/gb.c Sun Feb 7 15:22:39 2021
@@ -308,7 +308,7 @@
qlock(&pauselock);
qunlock(&pauselock);
}
- if(dma > 0)
+ if(dma & DMAREADY)
t = dmastep();
else
t = step();
--- a/sys/src/games/gb/mem.c Sat Feb 6 04:50:06 2021
+++ b/sys/src/games/gb/mem.c Sun Feb 7 15:22:39 2021
@@ -15,7 +15,7 @@
u32int divclock;
int prish;
MBC3Timer timer, timerl;
-s8int dma;
+u8int dma;
u32int white;
u32int moncols[4];
@@ -175,7 +175,14 @@
case HDMAC:
if((mode & COL) == 0)
goto ff;
- dma = (v & 0x80) != 0 ? -1 : 1;
+ if(v & 0x80){
+ v &= 0x7f;
+ dma = DMAHBLANK;
+ }else if(dma){
+ v |= 0x80;
+ dma = 0;
+ }else
+ dma = DMAREADY;
break;
case NR10: v |= 0x80; goto snd;
case NR14: case NR24: v |= 0x38; goto snd;
@@ -534,6 +541,7 @@
reg[VBK] = 0xfe;
reg[SVBK] = 0xf8;
reg[IF] = 0xe0;
+ reg[HDMAC] = 0xff;
}
void
@@ -572,7 +580,7 @@
{
int i;
u16int sa, da;
-
+
sa = (reg[HDMASL] | reg[HDMASH] << 8) & 0xfff0;
da = (reg[HDMADL] | reg[HDMADH] << 8) & 0x1ff0 | 0x8000;
for(i = 0; i < 16; i++)
@@ -583,12 +591,9 @@
reg[HDMADL] += 16;
if((reg[HDMADL] & 0xf0) == 0)
reg[HDMADH]++;
- if((reg[HDMAC] & 0x7f) == 0)
+ if(--reg[HDMAC] == 0xff)
dma = 0;
- else{
- reg[HDMAC]--;
- if((reg[HDMAC] & 0x80) != 0)
- dma = 1;
- }
+ else if(dma & DMAHBLANK)
+ dma &= ~DMAREADY;
return 64;
}
--- a/sys/src/games/gb/ppu.c Sat Feb 6 04:50:06 2021
+++ b/sys/src/games/gb/ppu.c Sun Feb 7 15:22:39 2021
@@ -338,8 +338,8 @@
reg[IF] |= IRQLCDS;
t = hblclock + 456 * 2 - clock;
addevent(&evhblank, t < 0 ? 456 * 2 : t);
- if(dma < 0)
- dma = 1;
+ if(dma & DMAHBLANK)
+ dma |= DMAREADY;
break;
}
}
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2021-02-07 23:22 [9front] games/gb: various HDMA fixes Michael Forney
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