discuss about using opencore can bus ip core and develop with nios ii

recently, i am working on can bus communication of fpga. i downlownded an ip core from opencore. i use the ip core through c8051 interface. it is bulit in the system like:https://www.alteraforum.com/forum/attachment.php?attachmentid=7256 , i process the ip core in nios like this: void Write_Reg(alt_u8 addr, alt_u8 reg_data)

{

//write reg

ALE_LOW;

SJA_CS_HI;

RD_HI;

WR_HI;

ALE_HI;

PORT_OUT;

usleep(1);

IOWR_ALTERA_AVALON_PIO_DATA(CAN_DAT_BASE,addr);//写地址

usleep(1);

ALE_LOW;

SJA_CS_LOW;

WR_LOW;

usleep(1);

//PORT_IN;

IOWR_ALTERA_AVALON_PIO_DATA(CAN_DAT_BASE,reg_data);//写数据

WR_HI;

SJA_CS_HI;

ALE_HI;

}

alt_u8 Read_Reg(alt_u8 addr)

{ alt_u8 reg_data;

WR_HI;

SJA_CS_HI;

ALE_HI;

//read reg

ALE_LOW;

RD_HI;

WR_HI;

SJA_CS_HI;

ALE_HI;

usleep(1);

PORT_OUT;

IOWR_ALTERA_AVALON_PIO_DATA(CAN_DAT_BASE,0);//写地址

usleep(1);

ALE_LOW;

SJA_CS_LOW;

RD_LOW;

usleep(1);

PORT_IN;

reg_data=IORD_ALTERA_AVALON_PIO_DATA(CAN_DAT_BASE);//读数据

usleep(1);

RD_HI;

SJA_CS_HI;

return reg_data;

} simulate as its reading and writing timing.https://www.alteraforum.com/forum/attachment.php?attachmentid=7257 https://www.alteraforum.com/forum/attachment.php?attachmentid=7258 but it's always 0xff when i read from the SJA1000 regs no matter what value i write to its regs.