PD minimum buffer requirements for libosdp

[gandraX]

Hi,
I implemented libsodp (CP mode) on my device and connected two readers (PD) from different manufacturers. One of them has a Receive Buffer Size of 64B, and CP is unable to send any commands to it after the osdp_CAP command.
It fails in the function osdp_phy_packet_init because of this line:
exp_len = sizeof(struct osdp_packet_header) + 64; /* 64 is estimated */

Thus, libsodp requires the PD to have more than a 64B + header buffer.
I did not find explicit minimum rx buffer requirements for PD in the standard. Are there any?

Thank You

[sidcha]

The +64 has been around since epoch and probably needs a more careful assessment with all the things that we know today.

Please note: that number can be reduced but not removed.

[gandraX]

I looked at standard 2.1.5, specifically Chapter 2.6 on Packet Size Limits, and found the following sentence:

'The implementation of the standard message set requires all devices to be able to accept packets up to 128 bytes long and tolerate messages addressed to other devices with a total length not exceeding 1440 bytes.'

One could assume that a PD device needs to have at least a 128 byte buffer. However, I came across a Netronix reader with only a 64 byte buffer, which surprised me. As a result, I had to reduce the estimated size from 64 bytes to 32.

[sidcha]

This will be tracked at #219. Closing this discussion.