1 /***************************************************************************
3 * Open \______ \ ____ ____ | | _\_ |__ _______ ___
4 * Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
5 * Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
6 * Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
10 * Copyright (C) 2002 by Linus Nielsen Feltzing
12 * This program is free software; you can redistribute it and/or
13 * modify it under the terms of the GNU General Public License
14 * as published by the Free Software Foundation; either version 2
15 * of the License, or (at your option) any later version.
17 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
18 * KIND, either express or implied.
20 ****************************************************************************/
29 /**************************************************************************
30 ** The A/D conversion is done every tick, in three steps:
32 ** 1) On the tick interrupt, the conversion of channels 0-3 is started, and
33 ** the A/D interrupt is enabled.
35 ** 2) After the conversion is done (approx. 256*4 cycles later), an interrupt
36 ** is generated at level 1, which is the same level as the tick interrupt
37 ** itself. This interrupt will be pending until the tick interrupt is
39 ** When the A/D interrupt is finally served, it will read the results
40 ** from the first conversion and start the conversion of channels 4-7.
42 ** 3) When the conversion of channels 4-7 is finished, the interrupt is
43 ** triggered again, and the results are read. This time, no new
44 ** conversion is started, it will be done in the next tick interrupt.
46 ** Thus, each channel will be updated HZ times per second.
48 *************************************************************************/
50 static int current_channel
;
51 static unsigned short adcdata
[NUM_ADC_CHANNELS
];
53 static void adc_tick(void)
55 /* Start a conversion of channel group 0. This will trigger an interrupt,
56 and the interrupt handler will take care of group 1. */
59 ADCSR
= ADCSR_ADST
| ADCSR_ADIE
| ADCSR_SCAN
| 3;
62 void ADITI(void) __attribute__((interrupt_handler
));
69 if(current_channel
== 0)
71 adcdata
[0] = ADDRA
>> 6;
72 adcdata
[1] = ADDRB
>> 6;
73 adcdata
[2] = ADDRC
>> 6;
74 adcdata
[3] = ADDRD
>> 6;
77 /* Convert the next group */
78 ADCSR
= ADCSR_ADST
| ADCSR_ADIE
| ADCSR_SCAN
| 7;
82 adcdata
[4] = ADDRA
>> 6;
83 adcdata
[5] = ADDRB
>> 6;
84 adcdata
[6] = ADDRC
>> 6;
85 adcdata
[7] = ADDRD
>> 6;
90 unsigned short adc_read(int channel
)
92 return adcdata
[channel
];
97 ADCR
= 0x7f; /* No external trigger; other bits should be 1 according
104 /* Enable the A/D IRQ on level 1 */
105 IPRE
= (IPRE
& 0xf0ff) | 0x0100;
107 tick_add_task(adc_tick
);
109 sleep(2); /* Ensure valid readings when adc_init returns */