ADC voltage: battcheck 3 digits, fixed t1616, switched back to 8-bit internal volt unit

Before this branch, `voltage` was 6 bits: Volts * 10
A couple patches ago, I upgraded it to 16 bits: 65535 * Volts / 10.24
That costs too much extra ROM on attiny85 though, for extra precision
it doesn't even use... so I switched back to an 8-bit value.  It's still
more precise than before though: Volts * 40
... and battcheck displays an extra digit now, on devices with ROM for it.
... and battcheck waits a second to get a more accurate measurement
    before displaying the first value.  It has *much* less variation
    between first and later readings now.

Also:
- got t1616 builds working again (tested fc13 and thefreeman-boost-fwaa)
- upgraded t1616 voltage and temp to 12-bit (10 bits + 4x oversampling)
- removed expensive temp conversion from t1616 ADC interrupt
- recalibrated t1616 bogomips again; runs faster after interrupt fix
- increased t1616 internal VDD measurement resolution by 36% (1.5V Vref, not 1.1V)
- fixed sloppy setting of Vref bits

I still need to test / update other t1616 builds,
and fix all the t85 + t1634 code and build targets.

1 files changed, 15 insertions, 22 deletions

diff --git a/arch/avr32dd20.c b/arch/avr32dd20.c
index 998e9f6..2ac3526 100644
--- a/arch/avr32dd20.c
+++ b/arch/avr32dd20.c
@@ -1,8 +1,10 @@
-// arch/avr32dd20.h: avr32dd20 support header
+// arch/avr32dd20.h: avr32dd20 support functions
 // Copyright (C) 2023 Selene ToyKeeper
 // SPDX-License-Identifier: GPL-3.0-or-later
 #pragma once
 
+#include "arch/avr32dd20.h"
+
 ////////// clock speed / delay stuff //////////
 
 inline void mcu_clock_speed() {
@@ -137,12 +139,22 @@ inline uint16_t mcu_adc_result() {
     return ADC0.RES;
 }
 
-inline uint16_t mcu_vdd_raw2cooked(uint16_t measurement) {
+inline uint8_t mcu_vdd_raw2cooked(uint16_t measurement) {
+    // In : 65535 * (Vbat / 10) / 1.024V
+    // Out: uint8_t: Vbat * 40
+    // (add 80 to round up near a boundary)
+    uint8_t vbat40 = (uint16_t)(measurement + 80) / 160;
+    return vbat40;
+}
+
+#if 0
+inline uint16_t mcu_vdd_raw2fine(uint16_t measurement) {
     // In : 65535 * (Vbat / 10) / 1.024V
     // Out: 65535 * (Vbat / 10) / 1.024V
     // This MCU's native format is already correct
     return measurement;
 }
+#endif
 
 inline uint16_t mcu_temp_raw2cooked(uint16_t measurement) {
     // convert raw ADC values to calibrated temperature
@@ -164,29 +176,10 @@ inline uint16_t mcu_temp_raw2cooked(uint16_t measurement) {
 }
 
 inline uint8_t mcu_adc_lsb() {
-    // temp is right-aligned, voltage is 16-bit, both have a useful LSB
+    // volts and temp are both 16-bit, so the LSB is useful as-is
     return ADC0_RESL;
 }
 
-#ifdef USE_VOLTAGE_VDD
-uint8_t calc_voltage(uint16_t measurement) {
-    // calculate actual voltage: volts * 10
-    // FIXME
-    // ADC = 1.1 * 1024 / volts
-    // volts = 1.1 * 1024 / ADC
-    result = ((uint16_t)(2*1.1*1024*10)/(measurement>>6)
-              + VOLTAGE_FUDGE_FACTOR
-              #ifdef USE_VOLTAGE_CORRECTION
-                  + VOLT_CORR - 7
-              #endif
-              ) >> 1;
-    return result;
-}
-#elif defined(USE_VOLTAGE_VDDIO2)
-#elif defined(USE_VOLTAGE_VDDIO2)
-#else
-// hwdef must supply its own function
-#endif
 
 ////////// WDT //////////
 // this uses the RTC PIT interrupt instead of WDT,