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/*
* Copyright 2014-present Facebook. All Rights Reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
//#define DEBUG
//#define VERBOSE
#include "bitbang.h"
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include "facebook/log.h"
#define NANOSEC_IN_SEC (1000 * 1000 * 1000)
#define BITBANG_FREQ_MAX (500 * 1000 * 1000) /* 500M Hz */
#define BITBANG_FREQ_DEFAULT (1 * 1000 * 1000) /* 1M Hz */
#define MAX(a, b) (((a) > (b)) ? (a) : (b))
struct bitbang_handle {
bitbang_init_st bbh_init;
uint32_t bbh_half_clk; /* ns per clock cycle */
};
void bitbang_init_default(bitbang_init_st *init)
{
memset(init, sizeof(*init), 0);
init->bbi_clk_start = BITBANG_PIN_HIGH;
init->bbi_data_out = BITBANG_CLK_EDGE_FALLING;
init->bbi_data_in = BITBANG_CLK_EDGE_RISING;
init->bbi_freq = BITBANG_FREQ_DEFAULT;
}
bitbang_handle_st* bitbang_open(const bitbang_init_st *init)
{
bitbang_handle_st *hdl;
if (!init || !init->bbi_pin_f
|| !init->bbi_freq || init->bbi_freq > BITBANG_FREQ_MAX) {
LOG_ERR(EINVAL, "Invalid init structure");
return NULL;
}
hdl = calloc(1, sizeof(*hdl));
if (!hdl) {
return NULL;
}
hdl->bbh_init = *init;
hdl->bbh_half_clk = NANOSEC_IN_SEC / init->bbi_freq / 2;
LOG_DBG("Bitbang open with initial %s, data out at %s, data in at %s, "
"freq at %uHz, half clk %uns",
(init->bbi_clk_start == BITBANG_PIN_LOW) ? "LOW" : "HIGH",
(init->bbi_data_out == BITBANG_CLK_EDGE_RISING)
? "RISING" : "FALLING",
(init->bbi_data_in == BITBANG_CLK_EDGE_RISING)
? "RISING" : "FALLING",
init->bbi_freq, hdl->bbh_half_clk);
return hdl;
}
void bitbang_close(bitbang_handle_st *hdl)
{
free(hdl);
}
/*
* The threshold (ns) to use spin instead of nanosleep().
* Before adding the high resolution timer support, either spin or nanosleep()
* will not bring the process wakeup within 10ms. It turns out the system time
* update is also controlled by HZ (100).
* After I added the high resolution timer support, the spin works as the
* system time is updated more frequently. However, nanosleep() solution is
* still noticable slower comparing with spin. There could be some kernel
* scheduling tweak missing. Did not get time on that yet.
* For now, use 10ms as the threshold to determine if spin or nanosleep()
* is used.
*/
#define BITBANG_SPIN_THRESHOLD (10 * 1000 * 1000)
static int sleep_ns(uint32_t clk)
{
struct timespec req, rem;
int rc = 0;
if (clk <= BITBANG_SPIN_THRESHOLD) {
struct timespec orig;
rc = clock_gettime(CLOCK_MONOTONIC, &req);
orig = req;
while (!rc && clk) {
uint32_t tmp;
rc = clock_gettime(CLOCK_MONOTONIC, &rem);
tmp = (rem.tv_sec - req.tv_sec) * NANOSEC_IN_SEC;
if (rem.tv_nsec >= req.tv_nsec) {
tmp += rem.tv_nsec - req.tv_nsec;
} else {
tmp -= req.tv_nsec - rem.tv_nsec;
}
if (tmp >= clk) {
break;
}
clk -= tmp;
req = rem;
}
} else {
req.tv_sec = 0;
req.tv_nsec = clk;
while ((rc = nanosleep(&req, &rem)) == -1 && errno == EINTR) {
req = rem;
}
}
if (rc == -1) {
rc = errno;
LOG_ERR(rc, "Failed to sleep %u nanoseconds", clk);
}
return rc;
}
int bitbang_io(const bitbang_handle_st *hdl, bitbang_io_st *io)
{
int rc = 0;
uint32_t clk = hdl->bbh_half_clk;
const struct {
bitbang_pin_value_en value;
bitbang_clk_edge_en edge;
} clks[] = {
{BITBANG_PIN_HIGH, BITBANG_CLK_EDGE_FALLING},
{BITBANG_PIN_LOW, BITBANG_CLK_EDGE_RISING},
};
int clk_idx;
int n_clk = 0;
int n_bits = 0;
const uint8_t *dout = io->bbio_dout;
uint8_t *din = io->bbio_din;
int bit_pos = 7;
bitbang_pin_func pin_f = hdl->bbh_init.bbi_pin_f;
void *context = hdl->bbh_init.bbi_context;
if ((io->bbio_in_bits == 0 && io->bbio_din)
|| (io->bbio_in_bits > 0 && !io->bbio_din)) {
rc = EINVAL;
LOG_ERR(rc, "Incorrect in bits and in buffer");
goto out;
}
if ((io->bbio_out_bits == 0 && io->bbio_dout)
|| (io->bbio_out_bits > 0 && !io->bbio_dout)) {
rc = EINVAL;
LOG_ERR(rc, "Incorrect out bits and out buffer");
goto out;
}
if (io->bbio_in_bits == 0 && io->bbio_out_bits == 0) {
rc = EINVAL;
LOG_ERR(rc, "Both in and out bits are 0");
goto out;
}
if (hdl->bbh_init.bbi_clk_start == BITBANG_PIN_HIGH) {
clk_idx = 0;
} else {
clk_idx = 1;
}
/* set the CLK pin start position */
pin_f(BITBANG_CLK_PIN, clks[clk_idx].value, context);
/* clear the first byte of din */
if (din && io->bbio_in_bits) {
memset(din, 0, (io->bbio_in_bits + 7) / 8);
}
do {
if ((rc = sleep_ns(clk))) {
goto out;
}
/* output first */
if (hdl->bbh_init.bbi_data_out == clks[clk_idx].edge) {
if (dout && n_bits < io->bbio_out_bits) {
pin_f(BITBANG_DATA_OUT, (*dout >> bit_pos) & 0x1, context);
}
}
/* then, input */
if (hdl->bbh_init.bbi_data_in == clks[clk_idx].edge) {
if (din && n_bits < io->bbio_in_bits) {
*din |= (pin_f(BITBANG_DATA_IN, 0, context) & 0x1) << bit_pos;
}
}
if (++n_clk % 2 == 0) {
/* one bit for every 2 half clks */
n_bits ++;
if (bit_pos == 0) {
if (dout) {
dout++;
}
if (din) {
din++;
}
bit_pos = 7;
} else {
bit_pos --;
}
}
clk_idx = 1 - clk_idx;
pin_f(BITBANG_CLK_PIN, clks[clk_idx].value, context);
} while (n_bits < MAX(io->bbio_in_bits, io->bbio_out_bits));
out:
return -rc;
}
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