000_l6470_read_me.md 6.2KB
Arduino-6470 library revision 0.7.0 or above is required.
This software can be used with any L647x chip and the powerSTEP01. L647x and powerSTEP01 devices can not be mixed within a system. A flag in the library must be set to enable use of a powerSTEP01.
These devices use voltage PWMs to drive the stepper phases. Phase current is not directly controlled. Each microstep corresponds to a particular PWM duty cycle. The KVAL_HOLD register scales the PWM duty cycle.
This software assumes that all L6470 drivers are in one SPI daisy chain.
The hardware setup is:
MOSI from controller tied to SDI on the first device
SDO of the first device is tied to SDI of the next device
SDO of the last device is tied to MISO of the controller
all devices share the same SCK, SS\_PIN and RESET\_PIN
Each L6470 passes the data it saw on its SDI to its neighbor on the **NEXT** SPI cycle (8 bit delay).
Each L6470 acts on the **last** SPI data it saw when the SS\_PIN **goes high**.
The L6470 drivers operate in STEP_CLOCK mode. In this mode the direction and enable are done via SPI commands and the phase currents are changed in response to step pulses (generated in the usual way).
There are two different SPI routines used.
uint8_t L6470_Transfer(uint8_t data, int _SSPin, const uint8_t chain_position) is used to setup the chips and by the maintenance/status code. This code uses the Arduino-6470 library.
void L6470_Transfer(uint8_t L6470_buf[], const uint8_t length) is used by the set_directions() routine to send the direction/enable commands. The library is NOT used by this code.
HARDWARE/SOFTWARE interaction
Powering up a stepper and setting the direction are done by the same command. Can’t do one without the other.
All directions are set every time a new block is popped off the queue by the stepper ISR.
SPI transfers, when setting the directions, are minimized by using arrays and a SPI routine dedicated to this function. L6470 library calls are not used. For N L6470 drivers, this results in a N byte transfer. If library calls were used then N*N bytes would be sent.
Power up (reset) sequence:
Stepper objects are created before the setup() entry point is reached.
After the setup() entry point is reached and before the steppers are initialized, L6470_init() is called to do the following
If present, the hardware reset is pulsed.
The L6470_chain array is populated during setup(). This array is used to tell where in the SPI stream the commands/data for an stepper is positioned.
The L6470 soft SPI pins are initialized.
The L6470 chips are initialized during setup(). They can be re-initialized using the L6470_init_to_defaults() function
The steppers are NOT powered up during this sequence.
L6470_chain array
This array is used by all routines that transmit SPI data.
Location 0 - number of drivers in chain
Location 1 - axis index for first device in the chain (closest to MOSI)
...
Location N - axis index for last device in the N device long chain (closest to MISO)
Direction set and enable
The DIR_WRITE macros for the L6470 drivers are written so that the standard X, Y, Z and extruder logic used by the set_directions() routine is not altered. These macros write the correct forward/reverse command to the corresponding location in the array L6470_dir_commands.
At the end of the set_directions() routine, the array L6470_chain is used to grab the corresponding direction/enable commands out of the array L6470_dir_commands and put them in the correct sequence in the array L6470_buf. Array L6470_buf is then passed to the void L6470_Transfer function which actually sends the data to the devices.
Utilities and misc
The absolute position registers should accurately reflect Marlin’s stepper position counts. They are set to zero during initialization. G28 sets them to the Marlin counts for the corresponding axis after homing. NOTE – these registers are often the negative of the Marlin counts. This is because the Marlin counts reflect the logical direction while the registers reflect the stepper direction. The register contents are displayed via the M114 D command.
The L6470_monitor feature reads the status of each device every half second. It will report if there are any error conditions present or if communications has been lost/restored. The KVAL_HOLD value is reduced every 2 – 2.5 seconds if the thermal warning or thermal shutdown conditions are present.
M122 displays the settings of most of the bits in the status register plus a couple of other items.
M906 can be used to set the KVAL_HOLD register one driver at a time. If a setting is not included with the command then the contents of the registers that affect the phase current/voltage are displayed.
M916, M917 & M918
These utilities are used to tune the system. They can get you in the ballpark for acceptable jerk, acceleration, top speed and KVAL_HOLD settings. In general they seem to provide an overly optimistic KVAL_HOLD setting because of the lag between setting KVAL_HOLD and the driver reaching final temperature. Enabling the L6470_monitor feature during prints will provide the final useful KVAL_HOLD setting.
The amount of power needed to move the stepper without skipping steps increases as jerk, acceleration and top speed increase. The power dissipated by the driver increases as the power to the stepper increases. The net result is a balancing act between jerk, acceleration, top speed and power dissipated by the driver.
M916 - Increases KVAL_HOLD while moving one axis until get thermal warning. This routine is also useful for determining the approximate KVAL_HOLD where the stepper stops losing steps. The sound will get noticeably quieter as it stops losing steps.
M917 - Find minimum current thresholds. This is done by doing the following steps while moving an axis:
Decrease OCD current until overcurrent error
Increase OCD until overcurrent error goes away
Decrease stall threshold until stall error
Increase stall until stall error goes away
M918 - Increase speed until error or max feedrate achieved.