overriding HAL driver, alt_sys_init()

This is an old post but I thought I'd post my solution to this RS-485 issue in case someone else finds it useful.

I ended up modifying the altera_avalon_uart driver so that it could use the PIO to toggle the direction of the RS-485 transceiver. To do this I modified the uart write function, which I call co_avalon_rs485_write here, such that at the very beginning I put

IOWR_ALTERA_AVALON_PIO_DATA(GENERAL_PIO_BASE, 0x1);

to enable writes. Then just before the "return (len - count)" call I turn it back off. However it was also necessary to make sure the shift register had drained before toggling this bit back so what I have is,

/* If in blocking mode, wait for data to be sent out before puting

* the rs-485 transceiver into receive mode. */

if (!(flags & O_NONBLOCK)) {

/* wait for circular transmit buffer to drain to transmitter

* shift register */

while ((sp->tx_start != sp->tx_end)){

/* interrupts here drain tx_buffer until tx_start=tx_end */

}

/* setup to monitor status register */

base = sp->base;

status = IORD_CO_AVALON_RS485_STATUS(base);

/* wait for transmitter shift register to drain */

while(!(status & CO_AVALON_RS485_STATUS_TMT_MSK)) {

status = IORD_CO_AVALON_RS485_STATUS(base);

}

}

/* put rs-485 transceiver into receive mode */

IOWR_ALTERA_AVALON_PIO_DATA(GENERAL_PIO_BASE, 0x0);

/* return the number of bytes written */

return (len - count);