Erik Olieman / FastAnalogIn

Class similar to AnalogIn that uses burst mode to run continious background conversions so when the input is read, the last value can immediatly be returned.

Dependents:   KL25Z_FFT_Demo test_armmath KL25Z_FFT_Demo_tony KL25Z_FFT_Demo_tony ... more

Supported devices

  • LPC1768
  • LPC4088
  • LPC11u24
  • KLxx
  • K20D50M


When you read an AnalogIn object it will enable the corresponding ADC channel, depending on the implementation do either one or multiple measurements for more accuracy, and return that value to your program. This way the ADC is only active when it is required, and it is fairly straightforward. However the downside is, is that an ADC is relatively slow. On the LPC1768 it runs at 200kHz -> in that time it could also have done 500 instructions.


This library uses the 'burst' feature of the microcontroller. This allows the ADC on the background to perform the AD conversions without requiring intervention from the microcontroller's core. Also there are no interrupts used, so also your time-sensitive code is not affected.

What the burst feature does is check which AD-channels are enabled, and he converts the enabled AD-channels one at a time. The result he stores in a register, where each channel has its own register. So this library checks which pins are used (you may make several FastAnalogIn objects, both for different pins and for the same pin, generally not extremely useful, but it is supported), and enables the relevant channels.

Reading a pin is done exactly the same for the user as AnalogIn, the read and read_us functions both work the same, and also the float operator is supported. However now it doesn't have to start a new conversion, so minus some overhead it can almost directly return the last measured value, no need to wait on the ADC!


FastAnalogIn has a few extra options that normal AnalogIn does not have: specifically you can either choose to have a FastAnalogIn object enabled or disabled. This is done with either the enable(bool enabled) and disable() functions, where enable(false) is equal to disable(), or by adding a second true/false argument to the constructor to either have it enabled at the beginning or disabled. By default it will be enabled.

LPC1768 & LPC4088
When a FastAnalogIn object is enabled, its corresponding ADC channel is also being scanned by the ADC and so it works as described above. When it is disabled you can still use the read functions, only now it will only enable the ADC channel for one conversion (actually two since for some reason the first conversion seems a bit weird), and when that conversion is done it will disable it again.

Since the ADC has to do the conversions one channel at a time, it becomes slower per channel if you enable many channels. For example, if you want to sample a sensor at a very high rate, and you also want to monitor your battery voltage. Then there is no reason to run an AD conversion on your battery continiously, so you can disable that channel and only run it once in a while.

Multiple Fast instances can be declared of which only ONE can be continuous (all others must be non-continuous).

FastAnalogIn   speed(PTC2);           // Fast continuous
FastAnalogIn   temp1(PTC2, 0);        // Fast non-continuous.
FastAnalogIn   temp2(PTB3, 0);        // Fast non-continuous.


Of course there are always downsides present. The extra power consumption probably won't be relevant for most, but still it is there. Aditionally there is no median filter like the normal AnalogIn has. Finally if you use AnalogIn you know exactly when the conversion happened, with FastAnalogIn you only know it was recently done but not exactly when.

AnalogIn + FastAnalogIn

Don't run both AnalogIn and FastAnalogIn objects in parallel as the results are unpredictable.
Both objects modify microcontroller registers, and neither of them bothers to inform the other one.
That's also the reason the disable() function was added.

Mon Mar 21 07:41:52 2016 +0000
Fixed pinmapping of LPC1114

Who changed what in which revision?

UserRevisionLine numberNew contents of line
Sissors11:14744c4ac884 1#if defined(TARGET_LPC11UXX) || defined (TARGET_LPC11XX)
Sissors8:68082fdde730 2
Sissors8:68082fdde730 3#include "FastAnalogIn.h"
Sissors8:68082fdde730 4static inline int div_round_up(int x, int y)
Sissors8:68082fdde730 5{
Sissors8:68082fdde730 6 return (x + (y - 1)) / y;
Sissors8:68082fdde730 7}
Sissors8:68082fdde730 8
Sissors8:68082fdde730 9#define LPC_IOCON0_BASE (LPC_IOCON_BASE)
Sissors8:68082fdde730 10#define LPC_IOCON1_BASE (LPC_IOCON_BASE + 0x60)
Sissors8:68082fdde730 11#define MAX_ADC_CLK 4500000
Sissors8:68082fdde730 12
Sissors11:14744c4ac884 13#ifdef TARGET_LPC11UXX
Sissors8:68082fdde730 14static const PinMap PinMap_ADC[] = {
Sissors8:68082fdde730 15 {P0_11, ADC0_0, 0x02},
Sissors8:68082fdde730 16 {P0_12, ADC0_1, 0x02},
Sissors8:68082fdde730 17 {P0_13, ADC0_2, 0x02},
Sissors8:68082fdde730 18 {P0_14, ADC0_3, 0x02},
Sissors8:68082fdde730 19 {P0_15, ADC0_4, 0x02},
Sissors8:68082fdde730 20 {P0_16, ADC0_5, 0x01},
Sissors8:68082fdde730 21 {P0_22, ADC0_6, 0x01},
Sissors8:68082fdde730 22 {P0_23, ADC0_7, 0x01},
Sissors8:68082fdde730 23 {NC , NC , 0 }
Sissors8:68082fdde730 24};
Sissors11:14744c4ac884 25#else
Sissors11:14744c4ac884 26static const PinMap PinMap_ADC[] = {
Sissors11:14744c4ac884 27 {P0_11, ADC0_0, 2},
Sissors11:14744c4ac884 28 {P1_0 , ADC0_1, 2},
Sissors11:14744c4ac884 29 {P1_1 , ADC0_2, 2},
Sissors11:14744c4ac884 30 {P1_2 , ADC0_3, 2},
Sissors11:14744c4ac884 31 // {P1_3 , ADC0_4, 2}, -- should be mapped to SWDIO only
Sissors11:14744c4ac884 32 {P1_4 , ADC0_5, 1},
Sissors11:14744c4ac884 33 {P1_10, ADC0_6, 1},
Sissors11:14744c4ac884 34 {P1_11, ADC0_7, 1},
Sissors11:14744c4ac884 35 {NC , NC , 0}
Sissors11:14744c4ac884 36};
Sissors11:14744c4ac884 37#endif
Sissors8:68082fdde730 38
Sissors8:68082fdde730 39static int channel_usage[8] = {0,0,0,0,0,0,0,0};
Sissors8:68082fdde730 40
Sissors8:68082fdde730 41
Sissors8:68082fdde730 42
Sissors8:68082fdde730 43FastAnalogIn::FastAnalogIn(PinName pin, bool enabled)
Sissors8:68082fdde730 44{
Sissors8:68082fdde730 45 ADCnumber = (ADCName)pinmap_peripheral(pin, PinMap_ADC);
Sissors8:68082fdde730 46 if (ADCnumber == (uint32_t)NC)
Sissors8:68082fdde730 47 error("ADC pin mapping failed");
Sissors11:14744c4ac884 48
Sissors11:14744c4ac884 49 //Seriously software people, can't you guys never keep the namings the same?
Sissors11:14744c4ac884 50 #ifdef TARGET_LPC11UXX
Sissors8:68082fdde730 51 datareg = (uint32_t*) (&LPC_ADC->DR0 + ADCnumber);
Sissors11:14744c4ac884 52 #else
Sissors11:14744c4ac884 53 datareg = (uint32_t*) (&LPC_ADC->DR[ADCnumber]);
Sissors11:14744c4ac884 54 #endif
Sissors8:68082fdde730 55
Sissors8:68082fdde730 56 // Power up ADC
Sissors8:68082fdde730 57 LPC_SYSCON->PDRUNCFG &= ~ (1 << 4);
Sissors8:68082fdde730 58 LPC_SYSCON->SYSAHBCLKCTRL |= ((uint32_t)1 << 13);
Sissors8:68082fdde730 59
Sissors12:46fbc645de4d 60 #ifdef TARGET_LPC11UXX
Sissors8:68082fdde730 61 uint32_t pin_number = (uint32_t)pin;
Sissors8:68082fdde730 62 __IO uint32_t *reg = (pin_number < 32) ? (__IO uint32_t*)(LPC_IOCON0_BASE + 4 * pin_number) : (__IO uint32_t*)(LPC_IOCON1_BASE + 4 * (pin_number - 32));
Sissors12:46fbc645de4d 63 #else
Sissors12:46fbc645de4d 64 uint32_t offset = (uint32_t)pin & 0xff;
Sissors12:46fbc645de4d 65 __IO uint32_t *reg = (__IO uint32_t*)(LPC_IOCON_BASE + offset);
Sissors12:46fbc645de4d 66 #endif
Sissors12:46fbc645de4d 67
Sissors8:68082fdde730 68
Sissors8:68082fdde730 69 // set pin to ADC mode
Sissors8:68082fdde730 70 *reg &= ~(1 << 7); // set ADMODE = 0 (analog mode)
Sissors8:68082fdde730 71
Sissors8:68082fdde730 72 uint32_t clkdiv = div_round_up(SystemCoreClock, MAX_ADC_CLK) - 1;
Sissors8:68082fdde730 73
Sissors10:afc3b84dbbd6 74 LPC_ADC->CR = (LPC_ADC->CR & 0xFF) // keep current channels
Sissors8:68082fdde730 75 | (clkdiv << 8) // max of 4.5MHz
Sissors8:68082fdde730 76 | (1 << 16) // BURST = 1, hardware controlled
Sissors8:68082fdde730 77 | ( 0 << 17 ); // CLKS = 0, we stick to 10 bit mode
Sissors8:68082fdde730 78
Sissors8:68082fdde730 79 pinmap_pinout(pin, PinMap_ADC);
Sissors8:68082fdde730 80
Sissors8:68082fdde730 81 //Enable channel
Sissors8:68082fdde730 82 running = false;
Sissors8:68082fdde730 83 enable(enabled);
Sissors8:68082fdde730 84
Sissors8:68082fdde730 85}
Sissors8:68082fdde730 86
Sissors8:68082fdde730 87void FastAnalogIn::enable(bool enabled)
Sissors8:68082fdde730 88{
Sissors8:68082fdde730 89 //If currently not running
Sissors8:68082fdde730 90 if (!running) {
Sissors8:68082fdde730 91 if (enabled) {
Sissors8:68082fdde730 92 //Enable the ADC channel
Sissors8:68082fdde730 93 channel_usage[ADCnumber]++;
Sissors8:68082fdde730 94 LPC_ADC->CR |= (1<<ADCnumber);
Sissors8:68082fdde730 95 running = true;
Sissors8:68082fdde730 96 } else
Sissors8:68082fdde730 97 disable();
Sissors8:68082fdde730 98 }
Sissors8:68082fdde730 99}
Sissors8:68082fdde730 100
Sissors8:68082fdde730 101void FastAnalogIn::disable( void )
Sissors8:68082fdde730 102{
Sissors8:68082fdde730 103 //If currently running
Sissors8:68082fdde730 104 if (running) {
Sissors8:68082fdde730 105 channel_usage[ADCnumber]--;
Sissors8:68082fdde730 106
Sissors8:68082fdde730 107 if (channel_usage[ADCnumber]==0)
Sissors8:68082fdde730 108 LPC_ADC->CR &= ~(1<<ADCnumber);
Sissors8:68082fdde730 109 }
Sissors8:68082fdde730 110 running = false;
Sissors8:68082fdde730 111}
Sissors8:68082fdde730 112
Sissors8:68082fdde730 113unsigned short FastAnalogIn::read_u16( void )
Sissors8:68082fdde730 114{
Sissors8:68082fdde730 115 unsigned int retval;
Sissors8:68082fdde730 116 //If object is enabled return current value of datareg
Sissors8:68082fdde730 117 if (running)
Sissors8:68082fdde730 118 retval = *datareg;
Sissors8:68082fdde730 119
Sissors8:68082fdde730 120 //If it isn't running, enable it and wait until new value is written to datareg
Sissors8:68082fdde730 121 else {
Sissors8:68082fdde730 122 //Force a read to clear done bit, enable the ADC channel
Sissors8:68082fdde730 123 retval = *datareg;
Sissors8:68082fdde730 124 enable();
Sissors8:68082fdde730 125 //Wait until it is converted
Sissors8:68082fdde730 126 while(1) {
Sissors8:68082fdde730 127 retval = *datareg;
Sissors8:68082fdde730 128 if ((retval>>31) == 1)
Sissors8:68082fdde730 129 break;
Sissors8:68082fdde730 130 }
Sissors8:68082fdde730 131 //Disable again
Sissors8:68082fdde730 132 disable();
Sissors8:68082fdde730 133 }
Sissors8:68082fdde730 134
Sissors8:68082fdde730 135 //Do same thing as standard mbed lib, unused bit 0-3, replicate 4-7 in it
Sissors8:68082fdde730 136 retval &= ~0xFFFF003F;
Sissors8:68082fdde730 137 retval |= (retval >> 6) & 0x003F;
Sissors8:68082fdde730 138 return retval;
Sissors8:68082fdde730 139}
Sissors8:68082fdde730 140#endif //defined TARGET_LPC11UXX