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ubb-vga.c (delay): try to compensate for APB jitter (experimental)

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First, we extend all deadlines a litte to make sure we never have to
wait negative time. Second, we get the timer value at the end of the
wait and CPU-loop for the difference between the actual value and the
ideal (extended) value.
This commit is contained in:
Werner Almesberger 2011-05-03 12:09:24 -03:00
parent 72235b9212
commit 01d33e28a7
1 changed files with 6 additions and 0 deletions
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6
ubb-vga/ubb-vga.c
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@ -244,11 +244,17 @@ static void cleanup(void)
static void delay(uint16_t cycles) static void delay(uint16_t cycles)
{ {
static uint16_t next = 0; static uint16_t next = 0;
uint16_t t;
next += cycles; next += cycles;
TDHR(TIMER) = next; TDHR(TIMER) = next;
TFCR = 1 << (TIMER+16); TFCR = 1 << (TIMER+16);
while (!(TFR & (1 << (TIMER+16)))); while (!(TFR & (1 << (TIMER+16))));
t = next+24-TCNT(TIMER);
t >>= 1;
while (t--)
asm("");
} }