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Fix negative watt values (#5)

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Handle both 1's complement and signed magnitude methods of expressing negative numbers

Co-authored-by: Joe Rouvier <jrouvier@users.noreply.github.com>
This commit is contained in:
dailow
2022-09-04 20:46:31 -07:00
committed by GitHub
parent fbb4db543e
commit b5c7aab03b
1 changed files with 13 additions and 2 deletions
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15
src/emporia_vue_utility.h
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@@ -297,7 +297,8 @@ class EmporiaVueUtility : public Component, public UARTDevice {
int32_t watts;
// Read the instant watts value
watts = bswap32(mr->watts);
// (it's actually a 24-bit int)
watts = (bswap32(mr->watts) & 0xFFFFFF);
// Bit 1 of the left most byte indicates a negative value
if (watts & 0x800000) {
@@ -305,8 +306,18 @@ class EmporiaVueUtility : public Component, public UARTDevice {
// Exactly "negative zero", which means "missing data"
ESP_LOGI(TAG, "Instant Watts value missing");
return;
} else if (watts & 0xC00000) {
// This is either more than 12MW being returned,
// or it's a negative number in 1's complement.
// Since the returned value is a 24-bit value
// and "watts" is a 32-bit signed int, we can
// get away with this.
watts -= 0xFFFFFF;
} else {
// If we get here, then hopefully it's a negative
// number in signed magnitude format
watts = (watts ^ 0x800000) * -1;
}
watts -= 0x800000;
}
if ((watts >= WATTS_MAX) || (watts < WATTS_MIN)) {