At Donnerstag, 17. Juli 2003 20:56 Jean Delvare wrote: > I read the datasheet again and finally understood what I first got > wrong. I thought that the saa1064 had 8 R/W registers. Actually it has 8 > (5 in use) write only registers, and one read only register. This means > that you can't read back values you wrote in registers (not really > practical, but you can still read the driver's values). What's more, the > readable register doesn't seem to have an address. So whatever address > you try to read, you read this register. Since only one bit in this > register can be set, and it usually isn't, this explains why the i2cdump > command I asked you to try returned only 00 values. That's what I tried to explain - there's only one read register, and only one bit matters there :-) > I think that if you power-off the saa1064, power it on again and run the > i2cdump command once at this time, you will have all 00 bytes again, > *except* the first one which will be 80. Could you try that? It would > confirm my understanding is correct. Exactly - on first readout (_before_ loading the driver the first time, that's why I didn't notice) it says 0x80 in the first byte. > So, the way to detect it now seems clearer: > > 1* The most basic way is to read the whole range and say it is a saa1064 > if all bytes are 0x00 or 0x80 (that is, (a & 0x7F)==0). Well - why all bytes? Only the very first read ever returns 0x80. > 2* We can give it a greater confidence if the first read returns 0x80 > and the later ones return 0x00. I do something similar for the lm75 Yup that's what I thought, too - 0x80 followed by 0x00 > 3* Instead of 2*, we can re-read the same address if it returns 0x80 > once. It should return 0x00 next time, if it is a saa1064. As I said - it only returns 0x80 in case of a power loss (which is the case after powering up the device). You'd have to force a hardware power-off of the chip before it would return 0x80 ever again. > I like the ideas, but in fact 2* and 3* may not even be necessary. As > far as I know, there are no other chips in our package at the adresses > the saa1064 can use, so we don't need something bulletproof. Let's go > for 1* with maybe a bit of 2*. I'll do it or you can do it if you want. > If you do it, first checkout the latest version of sensors-detect and > send back a patch, not the whole file. The PCF8574A uses the range 0x38 to 0x3f, and detects a saa1064 as a pcf8574a when loaded first. I'll put the two-byte-sequence (0x80 followed by 0x00) into the module. Maybe you'll do something for sensors-detect? I hope this weekend I'll find time to finish "the rest" (in-module detection, doc, and finally a complete patchset). Greetings, Sascha
