MWC on 8MHz

[remoteme]

Hi !

I am addressing this to developers directy involved in MWC software development, who knows all the intimacies.
There is a chance to have such assignment soon, get it as a job, not a fancy hobby to trash when you see can't be done.
So it's do it, or fire me ...
The task is to make work the core of the mwc on a 8MHz 3.3V (wearable) machine. I don't want to hear it's impossible we must make it !
So far I identified the following possible approaches / facts:
- the simplest would be to force processor at 16MHz, but I am afraid can't be done... 168-10MU, single cell lipo power, requirements I can't change. Am I wrong and is this possible ?
- software changes: this is the way I want to go... how hard do you see it? Anything that can't be done at 8Mhz if all software timings are changed accordingly ? Giros only, no acc, baro or mag sensors should be supported. The partes affected seems to be ESC and servos timing logic, anything else ?

So, these are the cards, if anyone want to help me identifying all the places to change in MWC to make this possible, please PM me.
Of course discussions can continue here, not only PM.
Once done will post the sources as a branch of this project.

Thank you !

[timecop]

Switch to STM8S, which runs in-spec at >= 3.0V at 16MHz.

[remoteme]

Can't change hardware platform, sorry.
What so terrible to change timings at 8MHz? Servos 128 steps instead 256? Acceptable... ESC 244Hz refresh insetead 488? Even 50Hz are good !
Make me understand why avoiding 8MHz ?

[Alexinparis]

Hi,

I think it's possible.
As you said, it's just some tuning to do on the right timers.
The cycle time would be longer, but with a simple gyro config, it should run.

[remoteme]

Cycle time is in the 2700-3100 ballpark with the present hardware.

[mr.rc-cam]

the simplest would be to force processor at 16MHz, but I am afraid can't be done... 168-10MU, single cell lipo power, requirements I can't change. Am I wrong and is this possible ?

It sounds like you have decided to use the 8MHz CPU and will change the MWC code. However, if this does not work out then don't despair. Although it is not recommended in the datasheet, overclocking a 3.5V powered ATMEGA to 16MHz is low risk (other hobby projects have done it and it worked fine). So if you want to eliminate the software changes then just swap the xtal and try it out at 16MHz. However, the '168 may not have enough memory for a typical MWC (not impossible, but be careful of out-of-memory problems).

- Thomas

[JohnyGab]

Anyway, this guy here sale Arudnio Pro mini 3.3V 16mhz, ( He doesnt have read the spec ), and as I see, he never had any complain

[kos]

it is flying ... mutliwii with 328p @ 8mhz 3.3v

many thanks to the output rewrite . I had a hard time questioning the analogWrite function .

as i am unable to commit, here are the changes:

Sensors: the F_CPU macro that was not used for i2c

Code: Select all

### Eclipse Workspace Patch 1.0
#P trunk
Index: MultiWii_shared/Sensors.pde
===================================================================
--- MultiWii_shared/Sensors.pde   (révision 623)
+++ MultiWii_shared/Sensors.pde   (copie de travail)
@@ -120,7 +120,7 @@
     I2C_PULLUPS_DISABLE
   #endif
   TWSR = 0;                                    // no prescaler => prescaler = 1
-  TWBR = ((16000000L / I2C_SPEED) - 16) / 2;   // change the I2C clock rate
+  TWBR = ((F_CPU / I2C_SPEED) - 16) / 2;       // change the I2C clock rate
   TWCR = 1<<TWEN;                              // enable twi module, no interrupt
 }
 
@@ -450,7 +450,7 @@
 void Baro_update() {
   if (currentTime < bmp085_ctx.deadline) return;
   bmp085_ctx.deadline = currentTime;
-  TWBR = ((16000000L / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz, BMP085 is ok with this speed
+  TWBR = ((F_CPU / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz, BMP085 is ok with this speed
   switch (bmp085_ctx.state) {
     case 0:
       i2c_BMP085_UT_Start();
@@ -595,7 +595,7 @@
 void Baro_update() {
   if (currentTime < ms561101ba_ctx.deadline) return;
   ms561101ba_ctx.deadline = currentTime;
-  TWBR = ((16000000L / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz, MS5611 is ok with this speed
+  TWBR = ((F_CPU / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz, MS5611 is ok with this speed
   switch (ms561101ba_ctx.state) {
     case 0:
       i2c_MS561101BA_UT_Start();
@@ -630,7 +630,7 @@
 }
 
 void ACC_getADC () {
-  TWBR = ((16000000L / 400000L) - 16) / 2;
+  TWBR = ((F_CPU / 400000L) - 16) / 2;
   i2c_getSixRawADC(MMA7455_ADDRESS,0x00);
 
   ACC_ORIENTATION( ((int8_t(rawADC[1])<<8) | int8_t(rawADC[0])) ,
@@ -661,7 +661,7 @@
 }
 
 void ACC_getADC () {
-  TWBR = ((16000000L / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz, ADXL435 is ok with this speed
+  TWBR = ((F_CPU / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz, ADXL435 is ok with this speed
   i2c_getSixRawADC(ADXL345_ADDRESS,0x32);
 
   ACC_ORIENTATION( ((rawADC[1]<<8) | rawADC[0]) ,
@@ -717,7 +717,7 @@
 }
 
 void ACC_getADC () {
-  TWBR = ((16000000L / 400000L) - 16) / 2;  // Optional line.  Sensor is good for it in the spec.
+  TWBR = ((F_CPU / 400000L) - 16) / 2;  // Optional line.  Sensor is good for it in the spec.
   i2c_getSixRawADC(BMA180_ADDRESS,0x02);
   //usefull info is on the 14 bits  [2-15] bits  /4 => [0-13] bits  /4 => 12 bit resolution
   ACC_ORIENTATION( ((rawADC[1]<<8) | rawADC[0])/16 ,
@@ -758,7 +758,7 @@
 }
 
 void ACC_getADC(){
-  TWBR = ((16000000L / 400000L) - 16) / 2;
+  TWBR = ((F_CPU / 400000L) - 16) / 2;
   i2c_getSixRawADC(0x70,0x02);
   ACC_ORIENTATION( ((rawADC[1]<<8) | rawADC[0])/64 ,
                    ((rawADC[3]<<8) | rawADC[2])/64 ,
@@ -779,7 +779,7 @@
 }
 
 void ACC_getADC() {
-  TWBR = ((16000000L / I2C_SPEED) - 16) / 2; // change the I2C clock rate. !! you must check if the nunchuk is ok with this freq
+  TWBR = ((F_CPU / I2C_SPEED) - 16) / 2;// change the I2C clock rate. !! you must check if the nunchuk is ok with this freq
   i2c_getSixRawADC(0xA4,0x00);
 
   ACC_ORIENTATION(  ( (rawADC[3]<<2)        + ((rawADC[5]>>4)&0x2) ) ,
@@ -803,7 +803,7 @@
 }
 
 void i2c_ACC_getADC(){
-  TWBR = ((16000000L / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz
+  TWBR = ((F_CPU / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz
   i2c_getSixRawADC(LIS3A,0x28+0x80);
   ACC_ORIENTATION( ((rawADC[1]<<8) | rawADC[0])/4 ,
                    ((rawADC[3]<<8) | rawADC[2])/4 ,
@@ -827,7 +827,7 @@
 }
 
   void ACC_getADC () {
-  TWBR = ((16000000L / 400000L) - 16) / 2;
+  TWBR = ((F_CPU / 400000L) - 16) / 2;
   i2c_getSixRawADC(0x30,0xA8);
 
   ACC_ORIENTATION( ((rawADC[1]<<8) | rawADC[0])/16 ,
@@ -869,7 +869,7 @@
 }
 
 void Gyro_getADC () {
-  TWBR = ((16000000L / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz
+  TWBR = ((F_CPU / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz
   i2c_getSixRawADC(0XD2,0x80|0x28);
 
   GYRO_ORIENTATION( ((rawADC[1]<<8) | rawADC[0])/20  ,
@@ -904,7 +904,7 @@
 }
 
 void Gyro_getADC () {
-  TWBR = ((16000000L / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz
+  TWBR = ((F_CPU / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz
   i2c_getSixRawADC(ITG3200_ADDRESS,0X1D);
   GYRO_ORIENTATION( ((rawADC[0]<<8) | rawADC[1])/4 , // range: +/- 8192; +/- 2000 deg/sec
                     ((rawADC[2]<<8) | rawADC[3])/4 ,
@@ -928,7 +928,7 @@
   uint8_t axis;
   if ( currentTime < t ) return; //each read is spaced by 100ms
   t = currentTime + 100000;
-  TWBR = ((16000000L / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz
+  TWBR = ((F_CPU / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz
   Device_Mag_getADC();
   if (calibratingM == 1) {
     tCal = t;
@@ -1052,7 +1052,7 @@
 #if defined(MPU6050)
 
 void Gyro_init() {
-  TWBR = ((16000000L / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz
+  TWBR = ((F_CPU / 400000L) - 16) / 2; // change the I2C clock rate to 400kHz
   i2c_writeReg(MPU6050_ADDRESS, 0x6B, 0x80);             //PWR_MGMT_1    -- DEVICE_RESET 1
   delay(5);
   i2c_writeReg(MPU6050_ADDRESS, 0x19, 0x00);             //SMPLRT_DIV    -- SMPLRT_DIV = 0  Sample Rate = Gyroscope Output Rate / (1 + SMPLRT_DIV)
@@ -1155,7 +1155,7 @@
 
 uint8_t WMP_getRawADC() {
   uint8_t axis;
-  TWBR = ((16000000L / I2C_SPEED) - 16) / 2; // change the I2C clock rate
+  TWBR = ((F_CPU / I2C_SPEED) - 16) / 2;// change the I2C clock rate
   i2c_getSixRawADC(0xA4,0x00);
 
   if (micros() < (neutralizeTime + NEUTRALIZE_DELAY)) {//we neutralize data in case of blocking+hard reset state
@@ -1198,4 +1198,4 @@
   if (BARO) Baro_init();
   if (MAG) Mag_init();
   if (ACC) {ACC_init();acc_25deg = acc_1G * 0.423;}
-}
+}
\ Pas de retour chariot à la fin du fichier


Output.pde
motor 3 , 11 : same as promini 16mhz , but prescaler to 32 instead of 64
motor 9 , 10 : same as promicro with top and value div 2 (because we are running x2 slower )

1 writemotors :

Code: Select all

#if defined(PROMINI8MHZ)
     #if (NUMBER_MOTOR > 0) // Timer 1 A & B [1000:2000] => [8000:16000]
      OCR1A = motor[0]<<2; //  pin 9
    #endif
    #if (NUMBER_MOTOR > 1)
      OCR1B = motor[1]<<2; //  pin 10
    #endif
    #if (NUMBER_MOTOR > 2)
      #ifndef EXT_MOTOR_RANGE
        OCR2A = motor[2]>>3; //  pin 11
      #else
        OCR2A = ((motor[2]>>2) - 250) + 2;
      #endif
    #endif
    #if (NUMBER_MOTOR > 3)
      #ifndef EXT_MOTOR_RANGE
        OCR2B = motor[3]>>3; //  pin 3
      #else
        OCR2B = ((motor[3]>>2) - 250) + 2;
      #endif
    #endif
    #if (NUMBER_MOTOR > 4) //note: EXT_MOTOR_RANGE not possible here
      atomicPWM_PIN6_highState = ((motor[4]-1000)>>2)+5;
      atomicPWM_PIN6_lowState  = 245-atomicPWM_PIN6_highState;
      atomicPWM_PIN5_highState = ((motor[5]-1000)>>2)+5;
      atomicPWM_PIN5_lowState  = 245-atomicPWM_PIN5_highState;
    #endif
    #if (NUMBER_MOTOR > 6) //note: EXT_MOTOR_RANGE not possible here
      atomicPWM_PINA2_highState = ((motor[6]-1000)>>2)+5;
      atomicPWM_PINA2_lowState  = 245-atomicPWM_PINA2_highState;
      atomicPWM_PIN12_highState = ((motor[7]-1000)>>2)+5;
      atomicPWM_PIN12_lowState  = 245-atomicPWM_PIN12_highState;
    #endif
  #endif

2 initOutput :

Code: Select all

 #if defined(PROMINI8MHZ)
       #if (NUMBER_MOTOR > 0)
   
    TCCR1A |= (1<<WGM11); TCCR1A &= ~(1<<WGM10); TCCR1B |= (1<<WGM13);  // phase correct mode
      TCCR1B &= ~(1<<CS11); ICR1 |= 0x2000; // no prescaler & TOP to 16383;
      TCCR1A |= _BV(COM1A1); // connect pin 9 to timer 1 channel A
    #endif
    #if (NUMBER_MOTOR > 1)
      TCCR1A |= _BV(COM1B1); // connect pin 10 to timer 1 channel B
    #endif
    #if (NUMBER_MOTOR > 2)
      TCCR2A |= _BV(COM2A1) | _BV(CS21) | _BV(CS20); // connect pin 11 to timer 2 channel A prescale32
    #endif
    #if (NUMBER_MOTOR > 3)
      TCCR2A |= _BV(COM2B1) ; // connect pin 3 to timer 2 channel B
    #endif
    #if (NUMBER_MOTOR > 5)  // PIN 5 & 6 or A0 & A1
      initializeSoftPWM();
      #if defined(A0_A1_PIN_HEX) || (NUMBER_MOTOR > 6)
        pinMode(5,INPUT);pinMode(6,INPUT);     // we reactivate the INPUT affectation for these two PINs
        pinMode(A0,OUTPUT);pinMode(A1,OUTPUT);
      #endif
    #endif
  #endif

done :
serial - ok
timer 1 timer 2 - ok
quad - ok

to do:
servo - untested
sowtpwm - untested
tri / hex / octo - untested

here is the video of the first flight with multiwii 328p 8mhz : https://vimeo.com/37910708

here is the cycle time , ftdi usb connected and motor armed

[kos]

The task is to make work the core of the mwc on a 8MHz 3.3V (wearable) machine. I don't want to hear it's impossible
[..]
168-10MU, single cell lipo power, requirements I can't change. Am I wrong and is this possible ?
- software changes: this is the way I want to go... how hard do you see it? Anything that can't be done at 8Mhz if all software timings are changed accordingly

not that hard , with multiwii 2.0 and the above code an ATmega 168 @8mhz should fly as fine as an ATmega 328 @8mhz

[kos]

hi ,

some additional changes in the code , now you can upload to a 8mhz board without any change in the config file

Code: Select all

 #if defined(PROMINI)
 
    #if (F_CPU > 8000000)
          #if (NUMBER_MOTOR > 0)
              blablabla ...



edit : delete "MultiWii_2_0_preversion3.zip"