Interconnectivity
Page 6 of 22
Firmware Programming Guide for PDIUSBD12
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2.1.4 Main Loop - MAINLOOP.C
The Main Loop checks the event flags and passes to appropriate subroutine for further processing. It also
contains the code for human interface, such as LED and key scan.
2.1.5 Protocol Layer - CHAP_9.C, PROTODMA.C
The Protocol layer handles standard USB device requests, as well as specific vendor requests such as DMA and
TWAIN.
2.2 Porting the Firmware to Other CPU Platform
Below table shows the modifications on building blocks need to be done. There are two levels of porting. First is
Chapter 9 only, which is only make the firmware to pass enumeration by supporting standard USB requests. The
second level is full product development, this will involve product specific firmware code.
File Name
Chapter 9 Only
Product Level
EPPHAL.C
Port to hardware specific.
Port to hardware specific.
D12CI.C
No change.
No change.
CHAP_9.C
No change.
Product specific USB descriptors.
PROTODMA.C
No change.
Add vendor request supports if necessary.
ISR.C
No change.
Add product specific processing on Generic and
Main endpoints.
MAINLOOP.C
Depends on the CPU and system,
ports, timer and interrupt initialization
need to be rewritten.
Add product specific Main Loop processing.
There are CPU and compiler dependent pre-definitions in MAINLOOP.H:
#ifdef __C51__
#define SWAP(x) ((((x) & 0xFF) << 8) | (((x) >> 8) & 0xFF))
#else
#define SWAP(x) (x)
#define code
#define idata
#endif
Note the "SWAP" is necessary for micro-controllers, which are big endian format, such as 8031. The "code" and
"idata" is only necessary when using 8031 and Keil C compiler.
2.3 Using the Firmware in Polling Mode
It's very easy to use the firmware in polling mode. Inside the Main Loop, add following code:
if(interrupt_pin_low)
fn_usb_isr();
Normally ISR is initiated by hardware. In polling mode, the Main Loop detects interrupt pin's state, and invokes
ISR if necessary.
