While playing with some cheap USB to RS-232 converters which use counterfeit PL2303 chips I found a bug in acm code which was sitting there from initial release. This bug was causing sluggish response from serial devices, as well as random 0x0d and 0x06 error codes. The bug is now fixed and corrected version of the library has been posted on GitHub a moment ago.
As a side effect to aforementioned bug fix some new functionality is now available. First, ACM and PL2303 classes now have isReady() method which can be used to check if certain device has been enumerated, initialized, and ready for service. This method is now used in all sample sketches, see, for example, pl2303_tinygps.pde, line 98.
Another addition is a block of code which performs proper PL2303 initialization. It is a mix of Linux pl2303.c code and Windows Prolific driver USB protocol traces. This block was added during troubleshooting; it turned out that it doesn’t make any difference on PL2303-based devices that I have – either genuine or counterfeit. However, it is tempting to be able to simulate “proper” manufacturer-recommended behaviour in the code so I decided to keep the initialization. It is turned off by default; if desired, it can be added during compilation by defining PL2303_COMPAT (see cdcprolific.h, line 41 and cdcprolific.cpp, lines 159-179 ). The block adds ~500 bytes to the binary so don’t turn it on just in case.
Please check the new code with your devices and let me know if you can see any improvements or new issues.
Oleg.