From 8e89496101e8a9d8a799861690e99f72e732c057 Mon Sep 17 00:00:00 2001 From: Howard Su Date: Fri, 9 Oct 2020 15:55:44 +0800 Subject: [PATCH] Build LUT by fixed point math Step 1 to remove float from the code. LUT table can be perfect build by fixed point math. lut[i] = (float)i / ((float)255 / ((float)pwm_max - (float)pwm_min)) + pwm_min; can be converted to: lut[i] = (float)i * ((float)pwm_max - (float)pwm_min) / (float)255 + pwm_min; can be futher convert to: lut[i] = i * (pwm_max - pwm_min) / 255 + pwm_min; The second convertion is validated by a small test code. The first convertion has slight difference on lut[255] of some combinition of pwm_max and pwm_min, which I believe second fomula is more accurate. --- QCX-SSB.ino | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/QCX-SSB.ino b/QCX-SSB.ino index 5b0561d..469e32e 100644 --- a/QCX-SSB.ino +++ b/QCX-SSB.ino @@ -3159,6 +3159,14 @@ void fatal(const __FlashStringHelper* msg, int value = 0, char unit = '\0') { wdt_reset(); } +//refresh LUT based on pwm_min, pwm_max +void build_lut() +{ + for(uint16_t i = 0; i != 256; i++) // refresh LUT based on pwm_min, pwm_max + lut[i] = (i * (pwm_max - pwm_min)) / 255 + pwm_min; + //lut[i] = min(pwm_max, (float)106*log(i) + pwm_min); // compressed microphone output: drive=0, pwm_min=115, pwm_max=220 +} + void setup() { digitalWrite(KEY_OUT, LOW); // for safety: to prevent exploding PA MOSFETs, in case there was something still biasing them. @@ -3403,8 +3411,7 @@ void setup() if(!dsp_cap) volume = 0; // mute volume for unmodified QCX receiver - for(uint16_t i = 0; i != 256; i++) // refresh LUT based on pwm_min, pwm_max - lut[i] = (float)i / ((float)255 / ((float)pwm_max - (float)pwm_min)) + pwm_min; + build_lut(); show_banner(); // remove release number @@ -3835,9 +3842,7 @@ void loop() change = true; } if((menu == PWM_MIN) || (menu == PWM_MAX)){ - for(uint16_t i = 0; i != 256; i++) // refresh LUT based on pwm_min, pwm_max - lut[i] = (float)i / ((float)255 / ((float)pwm_max - (float)pwm_min)) + pwm_min; - //lut[i] = min(pwm_max, (float)106*log(i) + pwm_min); // compressed microphone output: drive=0, pwm_min=115, pwm_max=220 + build_lut(); } if(menu == CWTONE){ if(dsp_cap){ cw_offset = (cw_tone == 0) ? tones[0] : tones[1]; paramAction(SAVE, CWOFF); }