rpirena/spidev_py.c

#define PY_SSIZE_T_CLEAN
#include "Python.h"
#include <linux/spi/spidev.h>
#include <sys/ioctl.h>
#include <stdio.h>

#ifndef DEBUG
# define DEBUG 1
#endif
#define dprintf(lvl, fmt...) if (DEBUG >= lvl) fprintf(stderr, "spidev: " fmt)

static struct ssp_job {
	int fd;
	Py_ssize_t count;
	unsigned char *command;
	unsigned int flags;
} job = {
	.fd = -1
};

#define INVERT_BITS_OUT    0x00001000

static int set_job_fd(struct ssp_job *j, int fd)
{
	if (fd >= 0) {
		j->fd = fd;
		dprintf(2, "fd = %d\n", fd);
	}
	else if (j->fd < 0) {
		PyErr_SetString(PyExc_ValueError, "No file descriptor");
		return -1;
	}
	return 0;
}


static unsigned char buf[4096];
#define MAX_TRANSFER ((Py_ssize_t)sizeof(buf))

static inline __u32 bit_reverse(__u32 i)
{
	return (i>>7) & 0x01010101
	     | (i>>5) & 0x02020202
	     | (i>>3) & 0x04040404
	     | (i>>1) & 0x08080808
	     | (i<<1) & 0x10101010
	     | (i<<3) & 0x20202020
	     | (i<<5) & 0x40404040
	     | (i<<7) & 0x80808080
	     ;
}
static inline void bit_reverse_copy(void *d, void *s, int n)
{
	n = (n+3)>>2;
	__u32 *dd=d, *ss=s;
	while (n--)
		*(dd++) = bit_reverse(*(ss++));
}

static void hexdump(FILE *f, const char *header, const unsigned char *b, Py_ssize_t n)
{
	fprintf(stderr, "%s", header);
	for (int i=0; i<n; i++)
		fprintf(stderr, " %02x", b[i]);
	fprintf(stderr, "\n");
}

static int do_spi_transfer(struct ssp_job *j)
{
	static struct spi_ioc_transfer transfer;
	unsigned int n = 0;
	transfer.tx_buf = (__u64) j->command;
	transfer.rx_buf = (__u64) buf;
	if (j->count > MAX_TRANSFER)
		n = MAX_TRANSFER;
	else
		n = j->count;
	transfer.len = n;
	if (j->flags & INVERT_BITS_OUT) {
		bit_reverse_copy(buf, j->command, n);
		transfer.tx_buf = (__u64) buf;
	}
	else if (DEBUG >= 3) 
		memset(buf, 0x5a, MAX_TRANSFER);
	if (DEBUG >= 4 || n <= 128 && DEBUG >= 3)
		hexdump(stderr, "TX:", j->command, n);
	if (n && ioctl(j->fd, SPI_IOC_MESSAGE(1), &transfer) < 0)
		return -1;
	if (DEBUG>=4 || n<=128 && DEBUG>=3)
		hexdump(stderr, "RX:", buf, n);
	dprintf(2, "tranfered %d bytes, flags 0x%x\n", n, j->flags);
	j->count -= n;
	j->command += n;
	return 0;
}

static PyObject *set_mode(PyObject *self, PyObject *args, PyObject *kw)
{
	static char *arg_names[] = {"mode", "cpha", "cpol", "fd", NULL};
	int mode = 0, cpha = 0, cpol = 0, fd = -1;
	if (!PyArg_ParseTupleAndKeywords(args, kw, 
					 "|ippi", arg_names,
					 &mode, &cpha, &cpol, &fd))
		return NULL;
	if (set_job_fd(&job, fd))
		return NULL;
	if (cpha)
		mode |= SPI_CPHA;
	if (cpol)
		mode |= SPI_CPOL;

	__u8 val = mode & (SPI_CPHA|SPI_CPOL);
	if (ioctl(job.fd, SPI_IOC_WR_MODE, &val) < 0) {
		PyErr_SetFromErrno(PyExc_IOError);
		return NULL;
	}
	dprintf(1, "CPHA: 0x%lx  CPOL: 0x%lx\n", mode & SPI_CPHA, mode & SPI_CPOL);
	Py_RETURN_NONE;
}

static PyObject *set_lsb_first(PyObject *self, PyObject *args, PyObject *kw)
{
	static char *arg_names[] = {"mode", "fd", NULL};
	int mode = 0, fd = -1;
	if (!PyArg_ParseTupleAndKeywords(args, kw, "|pi", arg_names, &mode, &fd))
		return NULL;
	if (set_job_fd(&job, fd))
		return NULL;
	__u8 val = mode;
	if (ioctl(job.fd, SPI_IOC_WR_LSB_FIRST, &val) < 0) {
		PyErr_SetFromErrno(PyExc_IOError);
		return NULL;
	}
	dprintf(1, "lsb first mode %d\n", mode);
	Py_RETURN_NONE;
}

static PyObject *set_speed(PyObject *self, PyObject *args, PyObject *kw)
{
	static char *arg_names[] = {"hz", "fd", NULL};
	int hz = 0, fd = -1;
	if (!PyArg_ParseTupleAndKeywords(args, kw, "|ii", arg_names, &hz, &fd))
		return NULL;
	if (set_job_fd(&job, fd))
		return NULL;
	if (ioctl(job.fd, SPI_IOC_WR_MAX_SPEED_HZ, &hz) < 0) {
		PyErr_SetFromErrno(PyExc_IOError);
		return NULL;
	}
	dprintf(1, "speed %d Hz\n", hz);
	Py_RETURN_NONE;
}

static PyObject *sync_transfer(PyObject *self, PyObject *args, PyObject *kw)
{
	static char *arg_names[] = {"cmd", "csize", "rsize", "flags", "fd", NULL};
	Py_buffer cmd;
	Py_ssize_t csize = 0, rsize=MAX_TRANSFER;
	int fd=-1, flags=0;
	if (!PyArg_ParseTupleAndKeywords(args, kw, 
					 "y*|nnii", arg_names,
					 &cmd, &csize, &rsize, &flags, &fd))
		return NULL;
	if (set_job_fd(&job, fd))
		goto error;
	if (rsize>MAX_TRANSFER) {
		PyErr_SetString(PyExc_ValueError, "resp request too large");
		goto error;
	}
	if (csize && csize > cmd.len) {
		PyErr_SetString(PyExc_ValueError, "cmd too short");
		goto error;
	}
	if (!csize)
		csize = cmd.len;
	job.command = cmd.buf;
	job.flags = flags;
	int vsize = 0;
	while (csize) {
		vsize = csize;
		if (csize>MAX_TRANSFER)
			if (csize-MAX_TRANSFER < rsize)
				job.count = csize - rsize;
			else
				job.count = MAX_TRANSFER;
		else
			job.count = csize;
		csize -= job.count;
		if (do_spi_transfer(&job)<0) {
			PyErr_SetFromErrno(PyExc_IOError);
		error:
			PyBuffer_Release(&cmd);
			return NULL;
		}
	}
	PyBuffer_Release(&cmd);
	if (rsize > vsize)
		rsize = vsize;

	return Py_BuildValue("y#", buf+vsize-rsize, rsize);
}


static PyMethodDef methods[] = {
	{"set_mode",       (PyCFunction)set_mode,        METH_VARARGS | METH_KEYWORDS, "Set clock mode cpol and cpha."},
	{"set_speed",      (PyCFunction)set_speed,       METH_VARARGS | METH_KEYWORDS, "Set max speed in Hz."},
	{"set_lsb_first",  (PyCFunction)set_lsb_first,   METH_VARARGS | METH_KEYWORDS, "Set LSB first mode."},
	{"sync_transfer",  (PyCFunction)sync_transfer,   METH_VARARGS | METH_KEYWORDS, "Synchronous write/read"}, 
		
	{NULL, NULL, 0, NULL}        /* Sentinel */
};

static PyModuleDef module_def = {
	.m_base    = PyModuleDef_HEAD_INIT,
	.m_name    = "spidev",
	.m_doc     = "RPiRENA spi interface",
	.m_size    = -1,
	.m_methods = methods,
};

PyMODINIT_FUNC
PyInit_spidev(void)
{
	PyObject *m = PyModule_Create(&module_def);
	PyModule_AddIntMacro(m, INVERT_BITS_OUT);
	return m;
}