SPI baudrate of 100000 does not work reliably

[jerryneedell]

Using the current master, I found that I was getting confusing data for the STPME610 touch screen driver on a feather52832. No errors reported, but data was clearly getting garbled.
The default baud rate for this device is 100000 (100K). I tried raising the baudrate to 1000000 (1M) and it works normally. @jepler pointed out that this may be a know "feature" for the nrf52 and 100000 is just too slow.

The workaround is simple, I just wanted to alert folks and see how/if you wanted to deal with this

[ladyada]

by chance does it work ok with M0 - like is it an stmpe thing or a nrf52 thing?
dont forget the stmpe uses mode 3 or 1 (not the 'standard' mode 0)

[jerryneedell]

It woks on a feather m0 express. This driver has not been changed. I thought the stmpe610 used either mode 0 or 1 depending on its whim.

[ladyada]

ok tagged as nrf52 - those peripherals could have a bug. thanks :)

[arturo182]

While 100K is not a speed that the nRF supports, this code https://github.com/adafruit/circuitpython/blob/master/ports/nrf/common-hal/busio/SPI.c#L39 should bump it to 125K and it should work as expected, but I will try to see if anything goes wrong when that happens.

@jerryneedell could you try testing with 250K and 500K ?

[jerryneedell]

at 250K and 500K the performance is improved, but still gives bad readings. It works very well at 1M

[dhalbert]

@jerryneedell do you have Saleae or similar to check whether the requested freq is what's actually coming out on the SPI clock pin?

[jerryneedell]

@dhalbert yes - I'll try to make some measurements tonight or tomorrow.

[jerryneedell]

@dhalbert I captured some samples with the Salea - the clocks are generally as commanded, but at 250 - I occasionally saw a longer cycle at 238Khz and at 500 and occasional longer cycle at 454KHz
I did not see any notable deviations at 1Mhz.

[yk9]

im also using the nrf52832 with the STMPE610 . i can read the ID but im getting no data from the registers.
anyone had this problem?

[jerryneedell]

Are you using the latest version of the stmpe610 library - the default baud rate was changed to 1MHz. Can you post and example of the code you are using?

[yk9]

i think im using the last version , yes the baud is 1M
here is the example of the init:
void _SMTPE610_init(void)
{
uint8_t d ;
ts_hardware_init();
writeRegister8(SYS_CTRL1, SYS_CTRL1_RESET); // 0x03 / 0x02
for ( d=0; d<65; d++)
{
readRegister8(d);
}
writeRegister8(SYS_CTRL2, 0x00); // Enable TSC and ADC Blocks
writeRegister8(TSC_CTRL, 0x04); // X, Y mode
writeRegister8(TSC_CTRL, 0x05); // Enable Device, No tracking index, X, Y mode
writeRegister8(INT_EN, 0x01); // TOUCH_DETECT-Interrupt are enabled

writeRegister8(INT_EN, INT_EN_TOUCHDET);
writeRegister8(ADC_CTRL1, ADC_CTRL1_10BIT | (0x6 << 4)); // 96 clocks per conversion
writeRegister8(ADC_CTRL2, ADC_CTRL2_6_5MHZ);
writeRegister8(TSC_CFG, TSC_CFG_4SAMPLE | TSC_CFG_DELAY_1MS | TSC_CFG_SETTLE_5MS);
writeRegister8(TSC_FRACTION_Z, 0x6);
writeRegister8(FIFO_TH, 1);
writeRegister8(FIFO_STA, FIFO_STA_RESET);
writeRegister8(FIFO_STA, 0);    // unreset
writeRegister8(TSC_I_DRIVE, TSC_I_DRIVE_50MA);
writeRegister8(INT_STA, 0xFF); // reset all ints
writeRegister8(INT_CTRL, INT_CTRL_POL_HIGH | INT_CTRL_ENABLE);    

[jerryneedell]

ah - you are using the Arduino IDE -- My experience has been with the CircuitPython Library. I have used it on an nrf52832 with CircuitPython.

[yk9]

not arduino - IAR