1 files changed, 107 insertions, 0 deletions
diff --git a/src/stm32/adc.c b/src/stm32/adc.c
new file mode 100644
index 00000000..b24b9e06
--- /dev/null
+++ b/src/stm32/adc.c
@@ -0,0 +1,107 @@
+// ADC functions on STM32
+//
+// 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 "generic/armcm_timer.h" // udelay
+#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)
+};
+
+#if CONFIG_MACH_STM32F1
+#define CR2_FLAGS (ADC_CR2_ADON | (7 << ADC_CR2_EXTSEL_Pos) | ADC_CR2_EXTTRIG)
+#else
+#define CR2_FLAGS ADC_CR2_ADON
+#endif
+
+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
+    if (!is_enabled_pclock(ADC1_BASE)) {
+        enable_pclock(ADC1_BASE);
+        uint32_t aticks = 3; // 2.5-3.2us (depending on stm32 chip)
+        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 = CR2_FLAGS;
+
+#if CONFIG_MACH_STM32F1
+        // Perform calibration
+        udelay(timer_from_us(1));
+        ADC1->CR2 = ADC_CR2_CAL | CR2_FLAGS;
+        while (ADC1->CR2 & ADC_CR2_CAL)
+            ;
+#endif
+    }
+
+    gpio_peripheral(pin, GPIO_ANALOG, 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 | CR2_FLAGS;
+
+need_delay:
+    return timer_from_us(10);
+}
+
+// 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);
+}