Gigabeat S: Add charge current and battery temp readout in power management and display in the battery screen. Thermistor data was obtained experimentally from one pulled off a dead board and appears basically correct when read back on a working device (which requires letting it settle to ambient temperature - a long wait so not easy to do). Sending me more thermistors would help improve accuracy *fingers crossed that it's close enough*. :-) This commit does NOT add charging but is a step towards implementing it.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@17626 a1c6a512-1295-4272-9138-f99709370657

2 files changed, 69 insertions, 0 deletions

diff --git a/firmware/target/arm/imx31/gigabeat-s/adc-target.h b/firmware/target/arm/imx31/gigabeat-s/adc-target.h
index 0b74ad84eb..d5f60de3db 100644
--- a/firmware/target/arm/imx31/gigabeat-s/adc-target.h
+++ b/firmware/target/arm/imx31/gigabeat-s/adc-target.h
@@ -45,5 +45,7 @@
 #define ADC_READ_ERROR 0xFFFF
 
 void adc_done(void);
+int battery_adc_charge_current(void);
+unsigned int battery_adc_temp(void);
 
 #endif
diff --git a/firmware/target/arm/imx31/gigabeat-s/powermgmt-imx31.c b/firmware/target/arm/imx31/gigabeat-s/powermgmt-imx31.c
index 53996f8cd7..711bc0dc58 100644
--- a/firmware/target/arm/imx31/gigabeat-s/powermgmt-imx31.c
+++ b/firmware/target/arm/imx31/gigabeat-s/powermgmt-imx31.c
@@ -24,6 +24,37 @@
 #include "adc.h"
 #include "powermgmt.h"
 
+/**
+ * Fixed-point natural log
+ * taken from http://www.quinapalus.com/efunc.html
+ *  "The code assumes integers are at least 32 bits long. The (positive)
+ *   argument and the result of the function are both expressed as fixed-point
+ *   values with 16 fractional bits, although intermediates are kept with 28
+ *   bits of precision to avoid loss of accuracy during shifts."
+ */
+static long flog(int x)
+{
+    long t,y;
+
+    y=0xa65af;
+    if(x<0x00008000) x<<=16,              y-=0xb1721;
+    if(x<0x00800000) x<<= 8,              y-=0x58b91;
+    if(x<0x08000000) x<<= 4,              y-=0x2c5c8;
+    if(x<0x20000000) x<<= 2,              y-=0x162e4;
+    if(x<0x40000000) x<<= 1,              y-=0x0b172;
+    t=x+(x>>1); if((t&0x80000000)==0) x=t,y-=0x067cd;
+    t=x+(x>>2); if((t&0x80000000)==0) x=t,y-=0x03920;
+    t=x+(x>>3); if((t&0x80000000)==0) x=t,y-=0x01e27;
+    t=x+(x>>4); if((t&0x80000000)==0) x=t,y-=0x00f85;
+    t=x+(x>>5); if((t&0x80000000)==0) x=t,y-=0x007e1;
+    t=x+(x>>6); if((t&0x80000000)==0) x=t,y-=0x003f8;
+    t=x+(x>>7); if((t&0x80000000)==0) x=t,y-=0x001fe;
+    x=0x80000000-x;
+    y-=x>>15;
+    return y;
+}
+
+
 const unsigned short battery_level_dangerous[BATTERY_TYPES_COUNT] =
 {
     3450
@@ -55,3 +86,39 @@ unsigned int battery_adc_voltage(void)
     return ((adc_read(ADC_BATTERY) * 2303) >> 10) + 2400;
 }
 
+/* Returns battery charge current from ADC [milliamps] */
+int battery_adc_charge_current(void)
+{
+    /* Positive reading = charger to battery
+     * Negative reading = battery to charger terminal
+     * ADC reading -512-511 = -2875mA-2875mA */
+    unsigned int value = adc_read(ADC_CHARGER_CURRENT);
+    return (((int)value << 22) >> 22) * 2881 >> 9;
+}
+
+/* Returns battery temperature from ADC [deg-C] */
+unsigned int battery_adc_temp(void)
+{
+    unsigned int value = adc_read(ADC_BATTERY_TEMP);
+    /* E[volts] = value * 2.3V / 1023
+     * R[ohms] = E/I = E[volts] / 0.00002[A] (Thermistor bias current source)
+     *
+     * Steinhart-Hart thermistor equation (sans "C*ln^2(R)" term because it
+     * has negligible effect):
+     * [A + B*ln(R) + D*ln^3(R)] - 273.15 = 1 / T[°K]
+     *
+     * Coeffients that fit experimental data (one thermistor so far, one run):
+     * A = 0.0013002631685462800
+     * B = 0.0002000841932612330
+     * D = 0.0000000640446750919
+     *
+     * Fixed-point output matches the floating-point version for each ADC
+     * value.
+     */
+     int R = 2070000 * value;
+     long long ln = flog(R) + 83196;
+     long long t0 = 425890304133ll;
+     long long t1 = 1000000*ln;
+     long long t3 = ln*ln*ln / 13418057;
+     return ((32754211579494400ll / (t0 + t1 + t3)) - 27315) / 100;
+}