void BaseWedgeI2CBus::moduleRead(unsigned int module, uint8_t address,
int offset, int len, uint8_t *buf) {
CHECK_LE(offset, 255);
selectQsfp(module);
CHECK_NE(selectedPort_, NO_PORT);
// CP2112 uses addresses in the on-the-wire format, while we generally
// pass them around in Linux standard format.
address <<= 1;
// Note that we don't use the writeRead() command, since this
// locks up the CP2112 chip if it times out. We perform a separate write,
// followed by a read. This releases the I2C bus between operations, but
// that's okay since there aren't any other master devices on the bus.
// Also note that we can't read more than 128 bytes at a time.
dev_.writeByte(address, offset);
if (len > 128) {
dev_.read(address, MutableByteRange(buf, 128));
dev_.writeByte(address, offset + 128);
dev_.read(address, MutableByteRange(buf + 128, len - 128));
} else {
dev_.read(address, MutableByteRange(buf, len));
}
unselectQsfp();
}
void WedgeI2CBus::verifyBus(bool autoReset) {
// Make sure the I2C bus is functioning, and reset the CP2112 device if not.
//
// Immediately after wedge is powered on, the CP2112 device appears to be in
// a state where all I2C operations time out. (It doesn't actually signal
// anything on the I2C bus.) Resetting the chip fixes it.
//
// We have an AT24C64B EEPROM attached at address 0xa2 which we should always
// be able to read from successfully.
uint8_t tmpBuf[8];
try {
dev_->read(ADDR_EEPROM, MutableByteRange(tmpBuf, sizeof(tmpBuf)));
} catch (const UsbError& ex) {
// The read failed.
// Reset the device, and then confirm that we can read this time.
//
// Note: This can be slightly dangerous for other reasons. We have seen
// some 3M QSFP optics that can lock up and hold SDA low forever. If we
// reset the CP2112 chip with SDA held low it can't reset successfully,
// and disappears from the USB bus completely. (It never re-enumerates.)
// If the bus is in this state resetting the chip will make it completely
// inaccessible.
if (autoReset) {
try {
dev_->resetDevice();
} catch (const UsbDeviceResetError& ex2) {
}
} else {
VLOG(1) << "initial read from CP2112 failed; I2C bus appears hung";
throw;
}
}
}
void BaseWedgeI2CBus::moduleWrite(unsigned int module, uint8_t address,
int offset, int len, uint8_t *buf) {
selectQsfp(module);
CHECK_NE(selectedPort_, NO_PORT);
// CP2112 uses addresses in the on-the-wire format, while we generally
// pass them around in Linux standard format.
address <<= 1;
// The CP2112 can only write 61 bytes at a time, and we burn one for
// the offset
CHECK_LE(len, 60);
// XXX: surely there's an easier way to do this?
uint8_t output[61]; // USB buffer size;
output[0] = offset;
memcpy(output + 1, buf, len);
dev_.write(address, MutableByteRange(output, len + 1));
unselectQsfp();
}
