Lpc2000

Bertrik wrote:
> Just curious because I'm working on something similar...
> 
> How are you triggering the ADC?
Well I tried lots of different ways but found this line to be the 
fastest in my case.

#define ADC_CLK_60_50   0x0B00   // 60MHz/12 = 5.0mhz
#define ADC_SEL1  0x02  // Select ADC n.1
#define ADC_PDN         0x00200000 // bit 21 Power down (1 for power)
#define ADC_START_NOW		0x01000000 // bit 24 Start ADC now

AD0CR = ADC_CLK_60_50 | ADC_SEL1 | ADC_PDN | ADC_START_NOW;

> ADC burst mode looks a bit awkward because with (for example) 8-bit
Yep, I dont trust burst mode because if an interrupt takes over would 
you miss samples and hit over run? Not sure but what I have works nice.

> resolution, the ADC takes a sample every 9 ADC clocks, which makes
> it hard to get a nice round sampling rate.
> I tried to synchronise the ADC to a timer. This works and I make
> almost any sample rate I want, but it only works when the trigger
> signal is sent out to a pin.
Yep, been there done that, but you will only get 320k (from my testing, 
I have been wrong before.) sample at best compared to the 500k+ I am 
getting.

> How are you storing the ADC data?
I just use a for loop to loop through all the pixels

uint32_t tADC;
tADC = (AD0DR1 << 16) >> 22; // copy ADC out to get 10 bits.
cambuff[tIdx] = tADC; // store ADC in camera buffer.

> Just a tight loop polling the ADC? or a FIQ? something else?
I found that polling the done flag to be a waste of time. Limited me to 
that 320 samples again. I figured we know how many clocks it takes for 
a conversion so I just NOPed it plus some extras for pipeline things 
that I dont know enough about

The dreaded inline assembly which works awesome for me. It doesnt use 
any variables so thats good I guess.
e.g
#define NOP2 {__asm  {nop}\
              __asm  {nop}}

Some people may want to pipe up and say I am doing it all wrong. I dont 
care. That part of my project is complete and runs very fast within the 
noise specs.

I also fixed my intermittent bug. It was a spurious intterrupt. When I 
was starting the hardware camera shutter I was turning off the USB 
interrupt. This caused the usual issues.

The fix I copied from here worked a treat.
VICDefVectAddr = (unsigned long) default_interrupt_handler;// spurious 
interrupt handler

void default_interrupt_handler(void) __irq
{	// this does get called occasionally
	 return;
}

Cheers
Keith