lpc176x: Add ADC support

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

Author: KevinOConnor

src/lpc176x/Kconfig

@@ -6,6 +6,7 @@ config LPC_SELECT
     bool
     default y
     select HAVE_GPIO
+    select HAVE_GPIO_ADC
 
 config BOARD_DIRECTORY
     string

src/lpc176x/gpio.c

@@ -5,7 +5,9 @@
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
 #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_out_setup
 #include "internal.h" // gpio_peripheral
@@ -117,3 +119,92 @@ gpio_in_read(struct gpio_in g)
     LPC_GPIO_TypeDef *regs = g.regs;
     return !!(regs->FIOPIN & g.bit);
 }
+
+
+/****************************************************************
+ * Analog to Digital Converter (ADC) pins
+ ****************************************************************/
+
+static const uint8_t adc_pins[] = {
+    GPIO(0, 23), GPIO(0, 24), GPIO(0, 25), GPIO(0, 26),
+    GPIO(1, 30), GPIO(1, 31), GPIO(0, 3), GPIO(0, 2),
+};
+
+static const uint8_t adc_pin_funcs[] = {
+    1, 1, 1, 1, 3, 3, 2, 2
+};
+
+#define ADC_FREQ_MAX 13000000
+DECL_CONSTANT(ADC_MAX, 4095);
+
+struct gpio_adc
+gpio_adc_setup(uint8_t pin)
+{
+    // Find pin in adc_pins table
+    int chan;
+    for (chan=0; ; chan++) {
+        if (chan >= ARRAY_SIZE(adc_pins))
+            shutdown("Not a valid ADC pin");
+        if (adc_pins[chan] == 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 (!(LPC_SC->PCONP & (1<<12))) {
+        // Power up ADC
+        LPC_SC->PCONP |= 1<<12;
+        LPC_SC->PCLKSEL0 = (LPC_SC->PCLKSEL0 & ~(0x3<<24)) | (0x1<<24);
+        LPC_ADC->ADCR = adcr;
+    }
+
+    gpio_peripheral(GPIO2PORT(pin), pin % 32, adc_pin_funcs[chan], 0);
+
+    return (struct gpio_adc){ .cmd = adcr | (1 << chan) | (1 << 24) };
+}
+
+static uint32_t adc_status;
+
+// Try to sample a value. Returns zero if sample ready, otherwise
+// returns the number of clock ticks the caller should wait before
+// retrying this function.
+uint32_t
+gpio_adc_sample(struct gpio_adc g)
+{
+    uint32_t status = adc_status;
+    if (status == g.cmd) {
+        // Sample already underway - check if it is ready
+        uint32_t val = LPC_ADC->ADGDR;
+        if (val & (1<<31))
+            // Sample ready
+            return 0;
+        goto need_delay;
+    }
+    if (status)
+        // ADC busy on some other channel
+        goto need_delay;
+
+    // Start new sample
+    adc_status = g.cmd;
+    LPC_ADC->ADCR = g.cmd;
+
+need_delay:
+    return (65 * DIV_ROUND_UP(CONFIG_CLOCK_FREQ*4, ADC_FREQ_MAX)
+            + timer_from_us(10));
+}
+
+// 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;
+}
+
+// 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;
+}

src/lpc176x/gpio.h

@@ -19,4 +19,12 @@ struct gpio_in {
 struct gpio_in gpio_in_setup(uint8_t pin, int8_t pull_up);
 uint8_t gpio_in_read(struct gpio_in g);
 
+struct gpio_adc {
+    uint32_t cmd;
+};
+struct gpio_adc gpio_adc_setup(uint8_t pin);
+uint32_t gpio_adc_sample(struct gpio_adc g);
+uint16_t gpio_adc_read(struct gpio_adc g);
+void gpio_adc_cancel_sample(struct gpio_adc g);
+
 #endif // gpio.h