diff options
Diffstat (limited to 'src/lpc176x/adc.c')
| -rw-r--r-- | src/lpc176x/adc.c | 86 |
1 files changed, 68 insertions, 18 deletions
diff --git a/src/lpc176x/adc.c b/src/lpc176x/adc.c index 4484b59d..e5ce6a96 100644 --- a/src/lpc176x/adc.c +++ b/src/lpc176x/adc.c @@ -6,6 +6,7 @@ #include "LPC17xx.h" // LPC_PINCON #include "autoconf.h" // CONFIG_CLOCK_FREQ +#include "board/irq.h" // irq_save #include "board/misc.h" // timer_from_us #include "command.h" // shutdown #include "gpio.h" // gpio_adc_setup @@ -24,6 +25,17 @@ static const uint8_t adc_pin_funcs[] = { #define ADC_FREQ_MAX 13000000 DECL_CONSTANT(ADC_MAX, 4095); +// The lpc176x adc is extremely noisy. Implement a 5 entry median +// filter to weed out obviously incorrect readings. +static struct { + uint32_t adcr; + uint16_t pos; + uint16_t chan; + uint16_t samples[5]; +} adc_status; + +enum { ADC_DONE=0x0100 }; + struct gpio_adc gpio_adc_setup(uint8_t pin) { @@ -36,20 +48,37 @@ gpio_adc_setup(uint8_t pin) break; } - uint32_t prescal = DIV_ROUND_UP(CONFIG_CLOCK_FREQ*4, ADC_FREQ_MAX) - 1; - uint32_t adcr = (1<<21) | ((prescal & 0xff) << 8); if (!is_enabled_pclock(PCLK_ADC)) { // Power up ADC enable_pclock(PCLK_ADC); - LPC_ADC->ADCR = adcr; + uint32_t prescal = DIV_ROUND_UP(CONFIG_CLOCK_FREQ*4, ADC_FREQ_MAX) - 1; + LPC_ADC->ADCR = adc_status.adcr = (1<<21) | ((prescal & 0xff) << 8); + LPC_ADC->ADINTEN = 0xff; + adc_status.chan = ADC_DONE; + NVIC_SetPriority(ADC_IRQn, 0); + NVIC_EnableIRQ(ADC_IRQn); } gpio_peripheral(pin, adc_pin_funcs[chan], 0); - return (struct gpio_adc){ .cmd = adcr | (1 << chan) | (1 << 24) }; + return (struct gpio_adc){ .chan = chan }; } -static uint32_t adc_status; +// ADC hardware irq handler +void __visible +ADC_IRQHandler(void) +{ + uint32_t pos = adc_status.pos, chan = adc_status.chan & 0xff; + uint32_t result = (&LPC_ADC->ADDR0)[chan]; + if (pos >= ARRAY_SIZE(adc_status.samples)) + // All samples complete + return; + if (pos >= ARRAY_SIZE(adc_status.samples) - 2) + // Turn off burst mode + LPC_ADC->ADCR = adc_status.adcr | (1 << chan); + adc_status.samples[pos++] = (result >> 4) & 0x0fff; + adc_status.pos = pos; +} // Try to sample a value. Returns zero if sample ready, otherwise // returns the number of clock ticks the caller should wait before @@ -57,40 +86,61 @@ static uint32_t adc_status; uint32_t gpio_adc_sample(struct gpio_adc g) { - uint32_t status = adc_status; - if (status == g.cmd) { + uint32_t chan = adc_status.chan; + if (chan == g.chan) { // Sample already underway - check if it is ready - uint32_t val = LPC_ADC->ADGDR; - if (val & (1<<31)) + if (adc_status.pos >= ARRAY_SIZE(adc_status.samples)) // Sample ready return 0; goto need_delay; } - if (status) + if (!(chan & ADC_DONE)) // ADC busy on some other channel goto need_delay; // Start new sample - adc_status = g.cmd; - LPC_ADC->ADCR = g.cmd; + adc_status.pos = 0; + adc_status.chan = g.chan; + LPC_ADC->ADCR = adc_status.adcr | (1 << g.chan) | (1<<16); need_delay: - return (65 * DIV_ROUND_UP(CONFIG_CLOCK_FREQ*4, ADC_FREQ_MAX) - + timer_from_us(10)); + return ((64 * DIV_ROUND_UP(CONFIG_CLOCK_FREQ*4, ADC_FREQ_MAX) + * ARRAY_SIZE(adc_status.samples)) / 4 + timer_from_us(10)); } +#define ORDER(r1, r2) do { \ + if (r1 > r2) { uint32_t t = r1; r1 = r2; r2 = t; } \ + } while (0) + // Read a value; use only after gpio_adc_sample() returns zero uint16_t gpio_adc_read(struct gpio_adc g) { - adc_status = 0; - return (LPC_ADC->ADGDR >> 4) & 0x0fff; + adc_status.chan |= ADC_DONE; + // Perform median filter on 5 read samples + uint16_t *p = adc_status.samples; + uint32_t v0 = p[0], v4 = p[1], v1 = p[2], v3 = p[3], v2 = p[4]; + ORDER(v0, v4); + ORDER(v1, v3); + ORDER(v0, v1); + ORDER(v3, v4); + ORDER(v1, v3); + ORDER(v1, v2); + ORDER(v2, v3); + return v2; } // Cancel a sample that may have been started with gpio_adc_sample() void gpio_adc_cancel_sample(struct gpio_adc g) { - if (adc_status == g.cmd) - adc_status = 0; + uint32_t chan = adc_status.chan; + if (chan != g.chan) + return; + irqstatus_t flag = irq_save(); + LPC_ADC->ADCR = adc_status.adcr; + adc_status.chan = chan | ADC_DONE; + adc_status.pos = ARRAY_SIZE(adc_status.samples); + (&LPC_ADC->ADDR0)[chan & 0xff]; + irq_restore(flag); } |