On Mon, Feb 7, 2011 at 6:12 PM, Michael Plante <michael.pla...@gmail.com>wrote:
> Rodrigo Rosa wrote: > >> // write > >> numBytesToSend = 0; > >> output_buff[numBytesToSend++]=0x6E; > >> output_buff[numBytesToSend++]=0x01; > >> output_buff[numBytesToSend++]=0x80; > >> output_buff[numBytesToSend++]=0x6E; > >> output_buff[numBytesToSend++]=0x01; > >> output_buff[numBytesToSend++]=0x00; > >> numBytesSent = ftdi_write_data(&ftdic, output_buff, numBytesToSend); > > I am not as sure on the 0x6E as I could have been on the 0x1A and 0x2E. > You'll note the docs say that 0x1A's length is actually length-1, and > measured in bits, rather than bytes. Ditto 0x2E. But it's not clear on > 0x6E what "length" represents in the docs. Did you ever go look at AN108? > You really need to read that before you go any further; MPSSE is not as > straightforward on the host side as some other modes are. > I've been taking the commands (0x6E, etc) from AN108. > > Anyway, you'll need to experiment some. And synchronize by intentionally > sending bad commands periodically (FTCSPI does this, and so does my code). > I will sometimes send 0xAA and expect 0xFA,0xAA, and then the same with > 0xAB. Then you just read until you can't read anymore, and make sure you > find where it told you "bad command". In any case, try calling > ftdi_read_data() and ask for more data than you expect back, at least until > you get the hang of what to ACTUALLY expect. > > i was doing the sync, but not correctly. I was only reading once. Now i write 0xAA and read a lot, check through what was read to see if i find what i wanted. if not i write again and repeat. seems to work ok. > > >> returns: input_buff = [0xcc, 0x33, 0x0, 0x0, 0x0 ...] > > After how many iterations through the loop? Did the read ever time out, > maybe just sometimes? Have you checked that there isn't more data > available? Do you know that it's not returning what it should? Why is it > in a loop, and how do you know there's not more data waiting to be read at > the end of each loop (or less)? > > i put in a loop to make the scope work easier, i was just testing if the code had any effect on the TDI pin. > > >> i don't understand what this means. is there any doc regarding return > codes? > > input_buff cannot properly be called a return code, so maybe that's why > you're having trouble finding it? However many bytes numBytesRead is > (which > you STILL haven't told me) is how many bytes of input_buff was read out of > the FTDI's FIFO, which in turn come off the wire. But how that corresponds > to the number of bits is something I'm not as familiar with because I > always > ran MPSSE such that it counted bytes rather than bits (it was still serial, > but only granular to the nearest 8 bits). > > ok, my bad, i'm just getting started with this. the code above returns numBytesRead == 3, with all the reading set to 0xFF (the other values of input_buff are not modified during reading). from AN108 describing 0x6E "The TDO/DI pin is sampled for the duration of TMS and a byte containing the data is passed back at the end of TMS clocking" shouldn't i get at least one reading different from 0xFF? the scope shows that TDI goes 0 1 0 i haven't found a smart way to do this, i use an entire byte just to clock out one bit on TDI. I do this by running one clock on TMS (setting clock to zero clocks out 1, as you marked) with the value I wanted on TDI. this way I think i can manage to drag the JTAG state machine around. not very happy, but may work. > > >> i hooked up a scope to TDI and i'm getting what i expected, sort of... > it > a square wave with 25% duty cycle, i expected 50%... > > You need to measure period, too. And also say how you configured the > divisor. > > i'm working at 20kHz, verified that. i wanted to send the IDCODE instruction to the JTAG port of my device, in order the verify that the connection is up and working... i think i got the "send and execute JTAG instruction" part, but I still haven't found out how to read a response. thanks again, i truly appreciate your help. Regards, -- Rodrigo. -- libftdi - see http://www.intra2net.com/en/developer/libftdi for details. To unsubscribe send a mail to libftdi+unsubscr...@developer.intra2net.com
