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/*
* Copyright © 2011 Keith Packard <keithp@keithp.com>
*
* 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; version 2 of the License.
*
* 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.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
*/
#include <ao.h>
/*
* ATtiny USI as a SPI interface
*/
/*
* Transfer one byte in/out of the USI interface
*/
/* Three wire mode */
#define SPI_USICR_WM ((0 << USIWM1) | (1 << USIWM0))
#define SPI_USICR_CS ((1 << USICS1) | (0 << USICS0) | (1 << USICLK))
#define SPI_USICR_FAST_2 ((1 << USIWM0) | (1 << USITC))
#define SPI_USICR_FAST_1 ((1 << USIWM0) | (1 << USITC) | (1 << USICLK))
static uint8_t
ao_spi_transfer(uint8_t i)
{
/* Load data register */
USIDR = i;
#if 1
USISR = (1 << USIOIF);
do {
USICR = SPI_USICR_WM | SPI_USICR_CS | (1 << USITC);
} while ((USISR & (1 << USIOIF)) == 0);
#else
/* 8 clocks */
USICR = SPI_USICR_FAST_1;
USICR = SPI_USICR_FAST_2;
USICR = SPI_USICR_FAST_1;
USICR = SPI_USICR_FAST_2;
USICR = SPI_USICR_FAST_1;
USICR = SPI_USICR_FAST_2;
USICR = SPI_USICR_FAST_1;
USICR = SPI_USICR_FAST_2;
USICR = SPI_USICR_FAST_1;
USICR = SPI_USICR_FAST_2;
USICR = SPI_USICR_FAST_1;
USICR = SPI_USICR_FAST_2;
USICR = SPI_USICR_FAST_1;
USICR = SPI_USICR_FAST_2;
USICR = SPI_USICR_FAST_1;
USICR = SPI_USICR_FAST_2;
#endif
/* Pull data from the port */
return USIDR;
}
/* Send bytes over SPI.
*
* This just polls; the SPI is set to go as fast as possible,
* so using interrupts would take way too long
*/
void
ao_spi_send_bus(void __xdata *block, uint16_t len) __reentrant
{
uint8_t *d = block;
while (len--)
ao_spi_transfer (*d++);
}
/* Receive bytes over SPI.
*
* Poll, sending zeros and reading data back
*/
void
ao_spi_recv_bus(void __xdata *block, uint16_t len) __reentrant
{
uint8_t *d = block;
while (len--)
*d++ = ao_spi_transfer (0xff);
}
/*
* Initialize USI
*
* Chip select is the responsibility of the caller
*/
void
ao_spi_init(void)
{
#if 1
USICR = (1 << USIWM0) | (1 << USICS1) | (1 << USICLK);
#else
USICR = SPI_USICR_FAST_2;
#endif
SPI_DIR &= ~(1 << DDB0); /* DI */
SPI_DIR |= (1 << DDB1); /* DO */
SPI_DIR |= (1 << DDB2); /* SCLK */
}
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