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8 years ago.
Fast I/O with STM32F103RB
Hello everybody,
please excuse my bad english, I'm a native speaking german. Because of interfacing hardware (shift registers and counters) using bit banging and a STM32F103RB I need to have faster I/O operations than the "DigitalOut".
With Nucleo Board Nucleo-F401RE Board there is no problem to use the library "FastIO". Is there any existing port to F103 or is there an other solution to something quicker than DigitalOut ?
Nice regards,
Ralph
3 Answers
8 years ago.
I dont know your hardware setup, but if you need to send data to a shiftregister like the 74595 or similar you can use the SPI port and transfer the data in chunks of 8 bits or more. SPI can also be used with DMA so that would need very little CPU overhead. Obviously bitbanging/fastio gives you maximum control over the waveforms, but at the expense of speed and probably timing accuracy.
8 years ago.
As far as I am aware there is no alternative library (but then again I don't know every library around here, I wanted to track such stuff in the cookbook, but mbed staff decided to freeze the cookbook).
Option A: Check if you remove the #ifdef for each of the existing two STM implementations if it works. Maybe they are sufficiently similar.
Option B: If that does not work, see if with the reference manual you can program it yourself
Option C: Send me an F103 and I do it for you :P. (I don't have it myself, so unless it is really exactly the same only they changed some names, I simply can't do it without a board).
Hello Erik,
Thank you for the great FastIO library. Below is my humble attempt to contribute for the NUCLEO-F103RB boards. I did not have chance to perform thorough tests but the basic bench results are attached.
Zoltan
FastIO_NUCLEO-F103RB.h
#if defined(TARGET_STM32F103RB)
#include "mbed.h"
#include "pinmap.h"
typedef struct {
uint32_t mask;
} fastio_vars;
#define PINMASK (1 << STM_PIN(pin))
#define PORT ((GPIO_TypeDef*)(GPIOA_BASE + 0x0400 * STM_PORT(pin)))
#define PIN_FUNCTION_GPIOMODE(gpiomode) \
uint32_t pull = PullNone; \
__IO uint32_t* gpio_reg_hl; \
uint32_t shift; \
\
if (STM_PIN(pin) < 8) { \
shift = (STM_PIN(pin) * 4); \
gpio_reg_hl = &(PORT->CRL); \
} else { \
shift = (STM_PIN(pin) % 8) * 4; \
gpio_reg_hl = &(PORT->CRH); \
} \
\
if ((!(*gpio_reg_hl & (0x03 << shift))) \
&& (!!(*gpio_reg_hl & (0x08 << shift))) \
&& (!(*gpio_reg_hl & (0x04 << shift)))) { \
if (!!(PORT->ODR & (0x01 << STM_PIN(pin)))) { \
pull = PullUp; \
} else { \
pull = PullDown; \
} \
} else { \
if (!!(*gpio_reg_hl & (0x04 << shift))) { \
pull = OpenDrain; \
} \
} \
\
pin_function(pin, STM_PIN_DATA(gpiomode, pull, 0));
#define SET_DIR_INPUT PIN_FUNCTION_GPIOMODE(0)
#define SET_DIR_OUTPUT PIN_FUNCTION_GPIOMODE(1)
#define INIT_PIN pin_function(pin, GPIO_MODE_INPUT); container.mask = PINMASK
#define DESTROY_PIN
#define SET_MODE(pull) pin_mode(pin, pull);
#define WRITE_PIN_SET (PORT->BSRR = PINMASK)
#define WRITE_PIN_CLR (PORT->BSRR = (PINMASK << 16))
#define READ_PIN ((PORT->IDR & container.mask) ? 1 : 0)
#endif
Test bench result:
Starting test bench
Verifying basic behavior
Basic behavior verified
Measuring fixed write pattern speed
Standard took 18.03 cycles, FastIO took 3.75 cycles, which is 21%
Standard took 250ns, FastIO took 52ns
Measuring variable write pattern speed
Standard took 22.03 cycles, FastIO took 12.54 cycles, which is 57%
Standard took 306ns, FastIO took 174ns
Measuring read speed
Standard took 21.05 cycles, FastIO took 10.02 cycles, which is 48%
Standard took 292ns, FastIO took 139ns
Measuring toggling using operators speed
Standard took 41.09 cycles, FastIO took 9.51 cycles, which is 23%
Standard took 571ns, FastIO took 132ns
Measuring switching between input and output
Standard took 692.61 cycles, FastIO took 594.35 cycles, which is 86%
Standard took 9620ns, FastIO took 8255ns
8 years ago.
May be this datasheet can help you: http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00161566.pdf
Ralph - try the $15 USD kit from XMOS (startKit). This CPU can really bit bang fast using a free C compiler. On this note, take care to not to be too fast with the XMOS CPU (can clock out at 100 Mhz if required).
http://www.digikey.com/product-search/en?keywords=xmos%20startkit
Caution: XMOS is not MBED enabled. It may make sense to interface your mbed board to the XMOS using SPI or similar. To start with, test the XMOS board as-is with your external digital I/O -> then marry with a mbed board if necessary.
posted by Sanjiv Bhatia 07 Apr 2016