stm32f4: Add support for ADC

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

src/stm32f4/Kconfig

@@ -6,6 +6,7 @@ config STM32F4_SELECT
     bool
     default y
     select HAVE_GPIO
+    select HAVE_GPIO_ADC
 
 config BOARD_DIRECTORY
     string

src/stm32f4/Makefile

@@ -15,6 +15,7 @@ src-y += stm32f4/main.c stm32f4/clock.c stm32f4/watchdog.c stm32f4/gpio.c
 src-y += generic/crc16_ccitt.c generic/alloc.c
 src-y += generic/armcm_irq.c generic/armcm_timer.c
 src-y += ../lib/stm32f4/system_stm32f4xx.c
+src-$(CONFIG_HAVE_GPIO_ADC) += stm32f4/adc.c
 src-$(CONFIG_SERIAL) += stm32f4/serial.c generic/serial_irq.c
 
 # Add assembler build rules

src/stm32f4/adc.c

@@ -0,0 +1,89 @@
+// ADC functions on STM32F4
+//
+// Copyright (C) 2019  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include "board/irq.h" // irq_save
+#include "board/misc.h" // timer_from_us
+#include "command.h" // shutdown
+#include "compiler.h" // ARRAY_SIZE
+#include "gpio.h" // gpio_adc_setup
+#include "internal.h" // GPIO
+#include "sched.h" // sched_shutdown
+
+DECL_CONSTANT("ADC_MAX", 4095);
+
+static const uint8_t adc_pins[] = {
+    GPIO('A', 0), GPIO('A', 1), GPIO('A', 2), GPIO('A', 3),
+    GPIO('A', 4), GPIO('A', 5), GPIO('A', 6), GPIO('A', 7),
+    GPIO('B', 0), GPIO('B', 1), GPIO('C', 0), GPIO('C', 1),
+    GPIO('C', 2), GPIO('C', 3), GPIO('C', 4), GPIO('C', 5)
+};
+
+struct gpio_adc
+gpio_adc_setup(uint32_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;
+    }
+
+    // Enable the ADC
+    enable_pclock(ADC1_BASE);
+    uint32_t aticks = 3; // 56 adc cycles
+    ADC1->SMPR1 = (aticks | (aticks << 3) | (aticks << 6) | (aticks << 9)
+                   | (aticks << 12) | (aticks << 15) | (aticks << 18)
+                   | (aticks << 21) | (aticks << 24));
+    ADC1->SMPR2 = (aticks | (aticks << 3) | (aticks << 6) | (aticks << 9)
+                   | (aticks << 12) | (aticks << 15) | (aticks << 18)
+                   | (aticks << 21) | (aticks << 24) | (aticks << 27));
+    ADC1->CR2 = ADC_CR2_ADON;
+
+    gpio_peripheral(pin, GPIO_ANALOG, 0, 0);
+
+    return (struct gpio_adc){ .chan = chan };
+}
+
+// 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 sr = ADC1->SR;
+    if (sr & ADC_SR_STRT) {
+        if (!(sr & ADC_SR_EOC) || ADC1->SQR3 != g.chan)
+            // Conversion still in progress or busy on another channel
+            goto need_delay;
+        // Conversion ready
+        return 0;
+    }
+    // Start sample
+    ADC1->SQR3 = g.chan;
+    ADC1->CR2 = ADC_CR2_SWSTART | ADC_CR2_ADON;
+need_delay:
+    return timer_from_us(4);
+}
+
+// Read a value; use only after gpio_adc_sample() returns zero
+uint16_t
+gpio_adc_read(struct gpio_adc g)
+{
+    ADC1->SR = ~ADC_SR_STRT;
+    return ADC1->DR;
+}
+
+// Cancel a sample that may have been started with gpio_adc_sample()
+void
+gpio_adc_cancel_sample(struct gpio_adc g)
+{
+    irqstatus_t flag = irq_save();
+    if (ADC1->SR & ADC_SR_STRT && ADC1->SQR3 == g.chan)
+        gpio_adc_read(g);
+    irq_restore(flag);
+}

src/stm32f4/gpio.h

@@ -21,4 +21,12 @@ struct gpio_in gpio_in_setup(uint32_t pin, int32_t pull_up);
 void gpio_in_reset(struct gpio_in g, int32_t pull_up);
 uint8_t gpio_in_read(struct gpio_in g);
 
+struct gpio_adc {
+    uint32_t chan;
+};
+struct gpio_adc gpio_adc_setup(uint32_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