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cwalter-at / freemodbus

BSD licensed MODBUS RTU/ASCII and TCP slave
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usRcvBufferPos reset only in STATE_RX_IDLE in mbrtu.c #23

Open tortuoise opened 3 years ago

tortuoise commented 3 years ago

Firstly, thanks to the authors for this nice concise modbus slave ported to multiple devices. I tested it on a MSP430F5529 so made a few changes to the provided MSP430F169 port. I got it working but only after addressing a couple of issues which I think should impact all devices. The issue I had to fix had to do with the current position of the buffer use to store received bytes (usRcvBufferPos) which only gets reset in STATE_RX_IDLE. If for whatever reason a slave doesn't respond to a request then the start position of the buffer doesn't get reset and is in an unknown state when the next request comes in. Setting it back to zero at the end of receiving the current frame seems to fix the problem though I'm not sure whether it introduces other problems.

eMBErrorCode eMBRTUReceive( UCHAR * pucRcvAddress, UCHAR ** pucFrame, USHORT * pusLength ) { ... usRcvBufferPos = 0; return eStatus; }

There's probably a better solution to this. Anybody else encounter this issue?

CyrilJiang commented 2 years ago

the timer and if no character is received within t3.5 we change to STATE_RX_IDLE. This makes sure that we delay startup of the modbus protocol stack until the bus is free.