之前使用NIOS II软核的SPI接口驱动了W25Q128，实现了数据保存。现在尝试使用SPI接口驱动网络芯片W5500，实现TCP的MODBUS。
前期卡了几天，主要问题还是出现在SPI驱动程序上。前面提到过，NIOS II软核自带了一个SPI的驱动函数，可以实现数据的读写，但和STM32的用法不太一样。于是我自作聪明，在原驱动函数的基础上做了改写，想写成一个每次收发一字节的SPI函数。如下：
alt_u8 user_avalon_spi_byte(alt_u32 base, alt_u32 slave,alt_u8 write_data)
{
alt_u32 status;
alt_u8 rd_data = 0;
IORD_ALTERA_AVALON_SPI_RXDATA(base);
do
{
status = IORD_ALTERA_AVALON_SPI_STATUS(base);
}
while ((status & ALTERA_AVALON_SPI_STATUS_TRDY_MSK) == 0 &&
(status & ALTERA_AVALON_SPI_STATUS_RRDY_MSK) == 0);
IOWR_ALTERA_AVALON_SPI_TXDATA(base, write_data);
if ((status & ALTERA_AVALON_SPI_STATUS_RRDY_MSK) != 0)
{
rd_data = IORD_ALTERA_AVALON_SPI_RXDATA(base);
}
// Wait until the interface has finished transmitting
do
{
status = IORD_ALTERA_AVALON_SPI_STATUS(base);
}
while ((status & ALTERA_AVALON_SPI_STATUS_TMT_MSK) == 0);
return rd_data;
}问题出在哪里？
使用这个函数，遇到的问题就是：SPI写操作是没问题的，但是读操作不行。现象就是：使用cmd命令，能够ping通W5500，有返回。但是无法做为服务端、客户端。
调了几天，把可能的选项都排除掉之后，瞄准了我自己写的SPI函数。换回NIOS II提供的SPI函数，再把W5500的驱动程序做了些调整，适配当前的SPI函数。然后上电，一切都没好了，至于说移植MODBUS什么的还没看出来问题，参照前面的文章就行：RT-Thread+W5500+freemodbus+TCP通信。
这是好用的函数，自我感觉我的函数就是限制了发送数量，同时进行数据的收发。除此之外，没有别的，但是目前没找到问题，后面再说吧。
int user_avalon_spi_byte(alt_u32 base, alt_u32 slave,
alt_u32 write_length, const alt_u8 * write_data,
alt_u32 read_length, alt_u8 * read_data,
alt_u32 flags)
{
const alt_u8 * write_end = write_data + write_length;
alt_u8 * read_end = read_data + read_length;
alt_u32 write_zeros = read_length;
alt_u32 read_ignore = write_length;
alt_u32 status;
/* We must not send more than two bytes to the target before it has
* returned any as otherwise it will overflow. */
/* Unfortunately the hardware does not seem to work with credits > 1,
* leave it at 1 for now. */
alt_32 credits = 1;
/* Warning: this function is not currently safe if called in a multi-threaded
* environment, something above must perform locking to make it safe if more
* than one thread intends to use it.
*/
// IOWR_ALTERA_AVALON_SPI_SLAVE_SEL(base, 1 << slave);
/* Set the SSO bit (force chipselect) only if the toggle flag is not set */
// if ((flags & ALT_AVALON_SPI_COMMAND_TOGGLE_SS_N) == 0) {
// IOWR_ALTERA_AVALON_SPI_CONTROL(base, ALTERA_AVALON_SPI_CONTROL_SSO_MSK);
// }
/*
* Discard any stale data present in the RXDATA register, in case
* previous communication was interrupted and stale data was left
* behind.
*/
IORD_ALTERA_AVALON_SPI_RXDATA(base);
/* Keep clocking until all the data has been processed. */
for ( ; ; )
{
do
{
status = IORD_ALTERA_AVALON_SPI_STATUS(base);
}
while (((status & ALTERA_AVALON_SPI_STATUS_TRDY_MSK) == 0 || credits == 0) &&
(status & ALTERA_AVALON_SPI_STATUS_RRDY_MSK) == 0);
if ((status & ALTERA_AVALON_SPI_STATUS_TRDY_MSK) != 0 && credits > 0)
{
credits--;
if (write_data < write_end)
IOWR_ALTERA_AVALON_SPI_TXDATA(base, *write_data++);
else if (write_zeros > 0)
{
write_zeros--;
IOWR_ALTERA_AVALON_SPI_TXDATA(base, 0);
}
else
credits = -1024;
};
if ((status & ALTERA_AVALON_SPI_STATUS_RRDY_MSK) != 0)
{
alt_u32 rxdata = IORD_ALTERA_AVALON_SPI_RXDATA(base);
if (read_ignore > 0)
read_ignore--;
else
*read_data++ = (alt_u8)rxdata;
credits++;
if (read_ignore == 0 && read_data == read_end)
break;
}
}
/* Wait until the interface has finished transmitting */
do
{
status = IORD_ALTERA_AVALON_SPI_STATUS(base);
}
while ((status & ALTERA_AVALON_SPI_STATUS_TMT_MSK) == 0);
/* Clear SSO (release chipselect) unless the caller is going to
* keep using this chip
*/
// if ((flags & ALT_AVALON_SPI_COMMAND_MERGE) == 0)
// IOWR_ALTERA_AVALON_SPI_CONTROL(base, 0);
return read_length;
}后面使用Modbus Poll软件模拟主机，读取数据一气呵成，随手放个图：
总的来说，W5500这个芯片的应用已经很成熟了，网上能搜到它的各种驱动和原理图。只要有一定的基础，照着操作，都不会出问题。
对了，有个地方注意下，就是端口号。
图上是502，每次断开之后重连，端口号需要加一，即变成503、504。这是在程序里写上的，如果不喜欢可以去掉，但是个人建议保存。