您好，我正在开发简单的 DSO，但 FT245 同步 FIFO 有问题。当我读取 4 字节确认时，从 FT245 读取正常工作，但是当我想检索采样数据时，它返回零字节（意味着 ftdi_read_data 返回 0，连续读取返回 -84 然后 -32（没有文档说明这些代码的含义））。
读取函数：
int Ft245sync::read(unsigned char * buf)
{
int res = ftdi_read_data(ftdic, buf, getReadChunkSize());
std::cerr << "res rd: " << res << std::endl;
return res;
}
发生读取的代码：
有效的部分（阅读确认）：
//send SET TRIGGER
recvbuf[0] = 0;
while(recvbuf[0] != DATA_OK)
{
unsigned char buf3[10] = { SET_TRIGGER, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
if(ft245.write(buf3) < 0)
{
std::cerr << "Error writing data3\n";
}
if(ft245.read(recvbuf) < 0)
{
std::cerr << "Error receiving data\n";
}
}
不起作用的部分：
//send START CAPTURE
unsigned char buf5[10] = { START_CAPTURE, 0x05, 0, 0, 0, 0, 0, 0, 0, 0 };
if(ft245.write(buf5) < 0)
{
std::cerr << "Error writing data5\n";
}
usleep(700);
std::cout << "Capture started\n";
for (int i = 0; i < 30; ++i)
{
if(ft245.read(recvbuf) < 0)
{
std::cerr << "Error reading data\n";
}
}
来自工作读取的chipscope的屏幕截图：
错误读取的屏幕截图：
可以看出，在两种情况下，在 TXE 变低两个时钟后，WR 都被置低。
部分 VHDL 工作代码如下：
when SEND_ACKNOWLEDGE0 =>
if to_boolean(ft245busy) then
state <= SEND_ACKNOWLEDGE0;
else
state <= SEND_ACKNOWLEDGE1;
end if;
when SEND_ACKNOWLEDGE1 =>
ft245rw <= '1';
responseCounter <= "000";
ft245din <= "10000000";
if (ft245wr = '0') then
state <= SEND_ACKNOWLEDGE2;
ft245strobe <= '0';
else
ft245strobe <= '1';
state <= SEND_ACKNOWLEDGE1;
end if;
when SEND_ACKNOWLEDGE2 =>
if (responseCounter < 1) then
responseCounter <= (responseCounter + 1);
ft245din <= "10000000";
state <= SEND_ACKNOWLEDGE2;
else
ft245dataWaitIn <= '1';
ft245rw <= '0';
responseCounter <= "000";
case command is
when "10101110" =>
state <= INIT0;
when "00010000" =>
state <= SET_VREF0;
when "00010001" =>
state <= SET_VLOG0;
when "00100000" =>
state <= SET_ATTENUATORS;
when "00100001" =>
state <= SET_COUPLINGS;
when "00110000" =>
state <= SET_DECIMATION;
when "00110001" =>
state <= SET_ANALOGTRIGGER;
when "00110010" =>
state <= SET_DIGITALTRIGGER;
when "01000000" =>
state <= START_CAPTURE;
when others =>
state <= IDLE;
end case;
end if;
部分错误读取：
when DUMP_DATA_PREPFT =>
if to_boolean(ft245busy) then
state <= DUMP_DATA_PREPFT;
else
state <= DUMP_DATA0;
end if;
when DUMP_DATA0 =>
adc1pd <= '1';
adc2pd <= '1';
ft245rw <= '1';
bufferDataDirection <= '0';
answerNumber <= "00";
ft245din <= "01010000";
if ((ft245wr = '0') and to_boolean(bufferReady)) then
state <= DUMP_DATA1;
ft245strobe <= '0';
else
ft245strobe <= '1';
state <= DUMP_DATA0;
end if;
when DUMP_DATA1 =>
ft245din <= "01010000";
ft245dataWaitIn <= '0';
answerNumber <= (answerNumber + 1);
if (answerNumber = 3) then
state <= DUMP_DATA2;
bufferOutputInputReady <= '1';
else
state <= DUMP_DATA1;
end if;
还有我的 ft245 控制器的代码负责读取（从 FPGA 的角度写入）：
when IDLE =>
if (strobe = '1') then
busy <= '1';
if (rw = '1') then
state <= WRITE_PREP;
else
state <= READ_PREP;
end if;
else
busy <= '0';
state <= IDLE;
end if;
when WRITE_PREP =>
if (txe = '0') then
state <= WRITE;
else
state <= WRITE_PREP;
end if;
when WRITE =>
if ((txe = '0') and (not to_boolean(dataWaitIn))) then
wr_int <= '0';
else
wr_int <= '1';
state <= IDLE;
busy <= '0';
end if;
并且有程序输出列表：
res wr: 10
res rd: 4
res wr: 10
Capture started
res rd: 0
res rd: 0
res rd: -84
Error reading data
res rd: -32
Error reading data
res rd: -32
...
从我的角度来看，FPGA中的一切都很好（根据chipscope）并且在程序中读取也是一样的，所以我不知道它为什么会起作用然后不知道（我可以成功地完成更多（数十个）写入/读取周期4字节确认，但它总是在这个错误读取时停止）......
//编辑：当您设置非常大的传入缓冲区（超过 16000 字节）时，它会出人意料地工作。但我还是不明白为什么..