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New A/D conversion strategy, now updates all channels every tick

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@5099 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Linus Nielsen Feltzing 2004-09-21 08:59:36 +00:00
parent 56cbda370d
commit ddb6333797
1 changed files with 59 additions and 41 deletions
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100
firmware/drivers/adc.c
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@ -22,6 +22,27 @@
#include "thread.h"
#include "adc.h"
/**************************************************************************
** The A/D conversion is done every tick, in three steps:
**
** 1) On the tick interrupt, the conversion of channels 0-3 is started, and
** the A/D interrupt is enabled.
**
** 2) After the conversion is done (approx. 256*4 cycles later), an interrupt
** is generated at level 1, which is the same level as the tick interrupt
** itself. This interrupt will be pending until the tick interrupt is
** finished.
** When the A/D interrupt is finally served, it will read the results
** from the first conversion and start the conversion of channels 4-7.
**
** 3) When the conversion of channels 4-7 is finished, the interrupt is
** triggered again, and the results are read. This time, no new
** conversion is started, it will be done in the next tick interrupt.
**
** Thus, each channel will be updated HZ times per second.
**
*************************************************************************/
static int current_channel;
static unsigned short adcdata[NUM_ADC_CHANNELS];
static const unsigned int adcreg[NUM_ADC_CHANNELS] =
@ -32,15 +53,39 @@ static const unsigned int adcreg[NUM_ADC_CHANNELS] =
static void adc_tick(void)
{
/* Read the data that has bee converted since the last tick */
adcdata[current_channel] =
*(unsigned short *)adcreg[current_channel] >> 6;
/* Start a conversion of channel group 0. This will trigger an interrupt,
and the interrupt handler will take care of group 1. */
/* Start a conversion on the next channel */
current_channel++;
if(current_channel == NUM_ADC_CHANNELS)
current_channel = 0;
ADCSR = ADCSR_ADST | current_channel;
current_channel = 0;
ADCSR = ADCSR_ADST | ADCSR_ADIE | ADCSR_SCAN | 3;
}
#pragma interrupt
void ADITI(void)
{
if(ADCSR & ADCSR_ADF)
{
ADCSR = 0;
if(current_channel == 0)
{
adcdata[0] = ADDRA >> 6;
adcdata[1] = ADDRB >> 6;
adcdata[2] = ADDRC >> 6;
adcdata[3] = ADDRD >> 6;
current_channel = 4;
/* Convert the next group */
ADCSR = ADCSR_ADST | ADCSR_ADIE | ADCSR_SCAN | 7;
}
else
{
adcdata[4] = ADDRA >> 6;
adcdata[5] = ADDRB >> 6;
adcdata[6] = ADDRC >> 6;
adcdata[7] = ADDRD >> 6;
}
}
}
unsigned short adc_read(int channel)
@ -48,44 +93,17 @@ unsigned short adc_read(int channel)
return adcdata[channel];
}
/* Batch convert 4 analog channels. If lower is true, convert AN0-AN3,
* otherwise AN4-AN7.
*/
static void adc_batch_convert(bool lower)
{
int reg = lower ? 0 : 4;
volatile unsigned short* ANx = ((unsigned short*) ADDRAH_ADDR);
int i;
ADCSR = ADCSR_ADST | ADCSR_SCAN | reg | 3;
/* Busy wait until conversion is complete. A bit ugly perhaps, but
* we should only need to wait about 4 * 14 µs */
while(!(ADCSR & ADCSR_ADF))
{
}
/* Stop scanning */
ADCSR = 0;
for (i = 0; i < 4; i++)
{
/* Read converted values */
adcdata[reg++] = ANx[i] >> 6;
}
}
void adc_init(void)
{
ADCR = 0x7f; /* No external trigger; other bits should be 1 according to the manual... */
ADCR = 0x7f; /* No external trigger; other bits should be 1 according
to the manual... */
ADCSR = 0;
current_channel = 0;
/* Do a first scan to initialize all values */
/* AN4 to AN7 */
adc_batch_convert(false);
/* AN0 to AN3 */
adc_batch_convert(true);
/* Enable the A/D IRQ on level 1 */
IPRE = (IPRE & 0xf0ff) | 0x0100;
tick_add_task(adc_tick);
}