PIC18F and PyUSB

I finally got a clearer idea on how to use the PyUSB libray. PyUSB is simply a python binding/wrapper for libusb. There are only few examples of python scripts I found on the net regarding the use of PyUSB. Also, the documentation for PyUSB is not that comprehensive yet.

On the USB device side, fortunately, Microchip has provide a LibUSB example for their PICDEM Full Speed USB demo board. Aside from the firmware for the PIC18F4550 family (includes PIC18F2550), they also provided a simple demo (Windows) application (with source codes for MSVC++ and Qt). It's a good opportunity to study LibUSB library along its generic usb device driver.
After some trial&errors on my python script, I finally made my PyQt GUI program working. (Most of my mistakes on the PyUSB module usage were the incorrect types of arguments used in the pyusb functions).

Below is my proto circuit. Basically it's the same circuit I used in my PIC18F2550 USB HID Mouse project. I only added two LEDs on RB0 and RB1 pins of pic18f2550. I also included a 10k potentiometer on RA0 pin (ADC ANA0).

I made a minimal modification on the LibUSB example firmware by Microchip so that it will be compatible with PyUSB demo python script:

 /*   
 Filename: main.c  
 */  
   
 /** INCLUDES *********************/  
 #include "Compiler.h"  
 #include "HardwareProfile.h"  
 #include "GenericTypeDefs.h"  
 #include "USB/usb_device.h"  
 #include "USB/usb.h"  
 #include "USB/usb_function_generic.h"  
 #include "usb_config.h"  
   
 /** CONFIGURATION ****************/  
 #pragma config PLLDIV  = 5     // (20 MHz crystal on PICDEM FS USB board)  
 #pragma config CPUDIV  = OSC1_PLL2    
 #pragma config USBDIV  = 2     // Clock source from 96MHz PLL/2  
 #pragma config FOSC   = HSPLL_HS  
 #pragma config FCMEN  = OFF  
 #pragma config IESO   = OFF  
 #pragma config PWRT   = OFF  
 #pragma config BOR   = ON  
 #pragma config BORV   = 3  
 #pragma config VREGEN  = ON   //USB Voltage Regulator  
 #pragma config WDT   = OFF  
 #pragma config MCLRE  = ON  
 #pragma config LPT1OSC = OFF  
 #pragma config PBADEN  = OFF  
 #pragma config STVREN  = ON  
 #pragma config LVP   = OFF  
 #pragma config XINST  = OFF    // Extended Instruction Set  
 #pragma config CP0   = OFF  
 #pragma config CP1   = OFF  
 #pragma config CPB   = OFF  
 #pragma config WRT0   = OFF  
 #pragma config WRT1   = OFF  
 #pragma config WRTB   = OFF    // Boot Block Write Protection  
 #pragma config WRTC   = OFF  
 #pragma config EBTR0  = OFF  
 #pragma config EBTR1  = OFF  
 #pragma config EBTRB  = OFF  
   
 /** VARIABLES ******************************************************/  
 #pragma udata USB_VARIABLES=0x500  
   
 unsigned char OUTPacket[64];     //User application buffer for receiving and holding OUT packets sent from the host  
 unsigned char INPacket[64];          //User application buffer for sending IN packets to the host  
 #pragma udata  
   
 USB_HANDLE USBGenericOutHandle;  
 USB_HANDLE USBGenericInHandle;  
 #pragma udata  
   
 /** PRIVATE PROTOTYPES *********************************************/  
 static void InitializeSystem(void);  
 void USBDeviceTasks(void);  
 void YourHighPriorityISRCode(void);  
 void YourLowPriorityISRCode(void);  
 void ProcessIO(void);  
   
 /** VECTOR REMAPPING ***********************************************/  
 #define REMAPPED_RESET_VECTOR_ADDRESS               0x00  
 #define REMAPPED_HIGH_INTERRUPT_VECTOR_ADDRESS     0x08  
 #define REMAPPED_LOW_INTERRUPT_VECTOR_ADDRESS     0x18  
   
 #pragma code REMAPPED_HIGH_INTERRUPT_VECTOR = REMAPPED_HIGH_INTERRUPT_VECTOR_ADDRESS  
 void Remapped_High_ISR (void)  
 {  
      _asm goto YourHighPriorityISRCode _endasm  
 }  
 #pragma code REMAPPED_LOW_INTERRUPT_VECTOR = REMAPPED_LOW_INTERRUPT_VECTOR_ADDRESS  
 void Remapped_Low_ISR (void)  
 {  
      _asm goto YourLowPriorityISRCode _endasm  
 }  
   
 #pragma code       
 //These are your actual interrupt handling routines.  
 #pragma interrupt YourHighPriorityISRCode  
 void YourHighPriorityISRCode()  
 {  
      USBDeviceTasks();  
 }     //This return will be a "retfie fast", since this is in a #pragma interrupt section   
 #pragma interruptlow YourLowPriorityISRCode  
 void YourLowPriorityISRCode()  
 {  
 }  
   
 /** DECLARATIONS ***************************************************/  
 #pragma code  
   
 //////////////////////////////////////////////////////////////////////  
 void main(void)  
 {    
   InitializeSystem();  
      USBDeviceAttach();  
   while(1)  
   {  
     ProcessIO();      
   }  
 }  
   
 static void InitializeSystem(void)  
 {  
      ADCON1 |= 0x0F;         // Default all pins to digital  
     
      USBGenericOutHandle = 0;       
      USBGenericInHandle = 0;            
   
   InitLEDs();  
      InitPot();  
   USBDeviceInit();     //usb_device.c. Initializes USB module SFRs and firmware variables to known states.  
 }  
   
 ////////////////////////////////////////////////////////////  
 void ProcessIO(void)  
 {  
   if((USBDeviceState < CONFIGURED_STATE)||(USBSuspendControl==1)) return;  
   if(!USBHandleBusy(USBGenericOutHandle))          //Check if the endpoint has received any data from the host.  
   {    
     switch(OUTPacket[0])     //Data arrived, check what kind of command might be in the packet of data.  
     {  
       case 0x80: // toggle LED1 (command from PC application)  
                     LED1 = !LED1;  
         break;  
       case 0x82: // toggle LED2  
                     LED2 = !LED2;  
         break;  
       case 0x81: //Get potentiometer position  
                     adc_status = 1;               // start a/d conversion  
         INPacket[0] = 0x81;  
                     while(adc_status);          // wait for the a/d conversion to complete (or use interrupt)  
                     INPacket[1] = ADRESH;     //read only 8-bit adc value (left justified)  
         if(!USBHandleBusy(USBGenericInHandle))            
                          USBGenericInHandle = USBGenWrite(USBGEN_EP_NUM,(BYTE*)&INPacket,USBGEN_EP_SIZE);       
         break;  
     }  
       
     USBGenericOutHandle = USBGenRead(USBGEN_EP_NUM,(BYTE*)&OUTPacket,USBGEN_EP_SIZE);  
   }  
 }//end ProcessIO  
   
   
 /*********** USB Callback Functions ****************/  
 void USBCBSuspend(void)  
 {       
 }  
   
 void USBCBWakeFromSuspend(void)  
 {  
 }  
   
 void USBCB_SOF_Handler(void)  
 {  
 }  
   
 void USBCBErrorHandler(void)  
 {  
 }  
   
 void USBCBCheckOtherReq(void)  
 {  
 }  
   
 void USBCBStdSetDscHandler(void)  
 {  
 }  
   
 void USBCBInitEP(void)  
 {  
   USBEnableEndpoint(USBGEN_EP_NUM,USB_OUT_ENABLED|USB_IN_ENABLED|USB_HANDSHAKE_ENABLED|USB_DISALLOW_SETUP);  
   USBGenericOutHandle = USBGenRead(USBGEN_EP_NUM,(BYTE*)&OUTPacket,USBGEN_EP_SIZE);  
 }  
   
 void USBCBSendResume(void)  
 {  
   static WORD delay_count;    
   USBResumeControl = 1;        // Start RESUME signaling    
   delay_count = 1800U;        // Set RESUME line for 1-13 ms  
   do{  
     delay_count--;  
   }while(delay_count);  
   USBResumeControl = 0;  
 }  
   
 BOOL USER_USB_CALLBACK_EVENT_HANDLER(USB_EVENT event, void *pdata, WORD size)  
 {  
   switch(event)  
   {  
     case EVENT_CONFIGURED:   
       USBCBInitEP();  
       break;  
     case EVENT_SET_DESCRIPTOR:  
       USBCBStdSetDscHandler();  
       break;  
     case EVENT_EP0_REQUEST:  
       USBCBCheckOtherReq();  
       break;  
     case EVENT_SOF:  
       USBCB_SOF_Handler();  
       break;  
     case EVENT_SUSPEND:  
       USBCBSuspend();  
       break;  
     case EVENT_RESUME:  
       USBCBWakeFromSuspend();  
       break;  
     case EVENT_BUS_ERROR:  
       USBCBErrorHandler();  
       break;  
     case EVENT_TRANSFER:  
       Nop();  
       break;  
     default:  
       break;  
   }     
   return TRUE;   
 }  

then, the generated hex code for PIC18F2550 device using C18 compiler:

 :020000040000FA  
 :060000008AEF0AF0120075  
 :0600080073EF08F0120086  
 :06001800BEEF08F012002B  
 :02002A000000D4  
 :04002C00D9CFE6FF43  
 :10003000E1CFD9FFE6526A6A686A160E6F6E9F0EAC  
 :100040006B6E7B0E696E6D8C6E6A000EE66EE66AF4  
 :10005000E66A710EE66E0F0EE66E70EC0AF00B6E3D  
 :10006000050EE15E0B506D9CDF6ADF500B6E0C6A73  
 :10007000080E0B5C000E0C5810E2DF50040DF3CF9D  
 :10008000E9FFF4CFEAFF000EE926040EEA22EE6A49  
 :10009000EE6AEE6AEE6ADF2AE8D7160E706E68A680  
 :1000A0000CD0030EE66E680EE66E0F0EE66E39ECAF  
 :1000B00008F0E552E552E552F2D70001736B786B18  
 :1000C000796B7A6B6D98080E6B6F040E6C6F616BB9  
 :1000D000606BE552E552E7CFD9FF1200D9CFE6FFBA  
 :1000E000E1CFD9FFE6520001600507E16DBA05D006  
 :1000F000686A69806988020E606F6850040B0FE0BF  
 :100100006950040B0CE0020EE66E680EE66E0F0EF0  
 :10011000E66E39EC08F0E552E552E552E9D86DA2F9  
 :1001200002D0A19AA1D06850010B1BE06950010BCD  
 :1001300018E07CDF0001040E606F0401200E026FE6  
 :10014000040E036F080E016F006B8C0E0013E66A3D  
 :10015000680EE66E0F0EE66E39EC08F0E552E552D9  
 :10016000E5526850100B0FE06950100B0CE0A4D85A  
 :10017000040EE66E680EE66E0F0EE66E39EC08F0C1  
 :10018000E552E552E5526850400B1DE06950400BC6  
 :100190001AE0010EE66EE66A000EE66EE66A020EF0  
 :1001A000E66EE66A7DEC09F00B6E060EE15E0B5022  
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 :1001C000E552E552E5526850200B04E06950200BDF  
 :1001D00001E04FD86850020B12E06950020B0FE0AB  
 :1001E000010EE66EE66A000EE66EE66AE668E6680E  
 :1001F0007DEC09F00B6E060EE15E0B506A6A040E90  
 :100200000001605D02E2A19A2FD069A62CD0DF6ABE  
 :10021000040EDF5C28E268A625D06CCF80F0030EC8  
 :10022000E66E680EE66E0F0EE66E39EC08F0E552EB  
 :10023000E552E552780E0001801502E178D810D021  
 :10024000000EE66EE66A800EE66E000EE66E010EA9  
 :10025000E66EE66A7DEC09F00B6E060EE15E0B5071  
 :10026000DF2AD6D700D0A19AE552E552E7CFD9FFD1  
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 :1002B000E552E552E55212006984040EE66E680EBE  
 :1002C000E66E0F0EE66E39EC08F0E552E552E552A7  
 :1002D0006D82000EE66EE66AE66EE66A040EE66E73  
 :1002E000E66A7DEC09F00B6E060EE15E0B50120023  
 :1002F000000EE66EE66AE66EE66A030EE66EE66AF3  
 :100300007DEC09F00B6E060EE15E0B506D92699468  
 :1003100068A40CD0020EE66E680EE66E0F0EE66E56  
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 :1004400009F00B6E060EE15E0B5079EF04F0020E20  
 :100450000001705D02E1ADDB1FD06CD8000181515D  
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 :1004700065C0E9FF66C0EAFF020EE926000EEA2227  
 :10048000200EEE6E040EED6E65C0E9FF66C0EAFF59  
 :100490008C0EEF6E01D0816B1200D9CFE6FFE1CF59  
 :1004A000D9FFE6526BC0E9FF6CC0EAFFEF50400B8A  
 :1004B00001E0010EDF6E00016B75080E605D0AE160  
 :1004C00022C46EFF6E50000803E2100E606F02D06F  
 :1004D000040E606F700528E16BC0E9FF6CC0EAFF95  
 :1004E000020EE926000EEA22280EEE6E040EED6ED4  
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 :10059000E16EE552E7CFD9FF120004012051600B54  
 :1005A000E842E842E842E842E842000901E058D067  
 :1005B00021510C0A54E00B0A43E00C0A35E0010A11  
 :1005C00026E00B0A22E0020A20E0030A1CE0080AE7  
 :1005D00010E0010A0CE00F0A08E0030A01E03FD036  
 :1005E0000001738F080E606F3BD0C8D839D07FDB15  
 :1005F00037D00001610E716F000E726F7381010EB2  
 :10060000746F738F2DD014D92BD02BD829D02451AF  
 :100610000001716F726B620E7127000E722373817D  
 :10062000010E746F738F1CD00001738F040124516D  
 :10063000EA6A620FE96E000EEA2222C4EFFF10D0D0  
 :10064000000EE66EE66AE66EE66A160EE66EE66A8C  
 :100650007DEC09F00B6E060EE15E0B5001D000D070  
 :100660001200D9CFE6FFE1CFD9FF040EE126040145  
 :10067000220510E120511F0B00090CE10001738FCE  
 :10068000030E0401215D04E10001010E7F6F02D021  
 :1006900000017F6B0401225167E120511F0B02080A  
 :1006A00063E124510F0B00095FE00001738F040127  
 :1006B00024BF10D024510F0BE96EEA6AD890E936B6  
 :1006C000EA36670EE926000EEA22EECFDEFFEDCF16  
 :1006D000DDFF0FD024510F0BE96EEA6AD890E9369E  
 :1006E000EA366B0EE926000EEA22EECFDEFFEDCFF2  
 :1006F000DDFF030E215D07E1DECFE9FFDDCFEAFF7D  
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 :10072000020EDBCFE9FF030EDBCFEAFFEE90ED52C6  
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 :10075000E9FFDDCFEAFF880EEF6EDF74DECFE9FF41  
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 :10077000E552E16EE552E7CFD9FF1200800E040189  
 :10078000205D55E10001C00E736F04012351030A7F  
 :100790002EE0010A0EE0030A03E00001736B47D06C  
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 :1007B0003ED02251F66EF76AD890F636F7363A0EEA  
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 :1007D00072F0020E0001F76A7125F66E7251F7226F  
 :1007E0000900F5CF74F00A00F5CF75F020D0030EA4  
 :1007F000225D1AE22251F66EF76AD890F636F73685  
 :100800003C0EF626140EF7220900F5CF71F00A000F  
 :10081000F5CF72F071C0F6FF72C0F7FF0800F55017  
 :100820000001746F756B02D00001736B00D0120071  
 :10083000D9CFE6FFE1CFD9FF020EE1260401286BF4  
 :10084000296B20511F0B020A12E0030A0DE0010A76  
 :1008500001E03BD00001738F0401288100017F0576  
 :1008600002E10401288331D00001738F2ED00001F2  
 :10087000738F040124BF10D024510F0BE96EEA6A74  
 :10088000D890E936EA36670EE926000EEA22EECF66  
 :10089000DEFFEDCFDDFF0FD024510F0BE96EEA6ACA  
 :1008A000D890E936EA366B0EE926000EEA22EECF42  
 :1008B000DEFFEDCFDDFFDECFE9FFDDCFEAFFEF505A  
 :1008C000040B02E0010E286F00D0000173AF07D0C7  
 :1008D000280E716F040E726F7381020E746F020E18  
 :1008E000E15C02E2E16AE552E16EE552E7CFD9FF51  
 :1008F00012006D98000173BF4AD078AF28D0020E65  
 :10090000706F6BC0E9FF6CC0EAFFEE52EF6A6BC01C  
 :10091000E9FF6CC0EAFFC80EEF6E65C0E9FF66C074  
 :10092000EAFFEE52080EEF6E65C0E9FF66C0EAFF0F  
 :10093000020EE926000EEA22280EEE6E040EED6E7F  
 :1009400065C0E9FF66C0EAFFC80EEF6E1FD065C044  
 :10095000E9FF66C0EAFFEE52080EEF6E65C0E9FFE0  
 :1009600066C0EAFF020EE926000EEA22200EEE6EB5  
 :10097000040EED6E65C0E9FF66C0EAFF8C0EEF6EF7  
 :100980006BC0E9FF6CC0EAFF840EEF6E86D078BFC3  
 :1009900084D0040120AF59D0000174510401265DB8  
 :1009A000000175510401275904E226C474F027C4DC  
 :1009B00075F074D80001010E706F65C0E9FF66C064  
 :1009C000EAFFEE52080EEF6E65C0E9FF66C0EAFF6F  
 :1009D000020EE926000EEA22200EEE6E040EED6EE7  
 :1009E00065C0E9FF66C0EAFF800EEF6E816B63C0F1  
 :1009F000E9FF64C0EAFFEE52080EEF6E63C0E9FF44  
 :100A000064C0EAFF020EE926000EEA22200EEE6E16  
 :100A1000040EED6E63C0E9FF64C0EAFF840EEF6E62  
 :100A2000010E816F6BC0E9FF6CC0EAFF020EE92680  
 :100A3000000EEA22280EEE6E040EED6E6BC0E9FF8A  
 :100A40006CC0EAFFC80EEF6E28D00001020E706F76  
 :100A50006BC0E9FF6CC0EAFFEE52EF6A6BC0E9FFC2  
 :100A60006CC0EAFFC80EEF6E65C0E9FF66C0EAFF22  
 :100A7000EE52080EEF6E65C0E9FF66C0EAFF020E97  
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 :100BA000E15C02E2E16AE552E16EE552E7CFD9FF8E  
 :100BB0001200D9CFE6FFE1CFD9FF020EE12663C0D4  
 :100BC000E9FF64C0EAFFEE52EFCFDFFFDFCF0BF0AB  
 :100BD0000B500001795D000E7A5903E279C0DFFF06  
 :100BE00009D0DF500B6E0C6A0B50795D796F0C5099  
 :100BF0007A597A6F010EDB6ADF50F36E010EDBCF9C  
 :100C0000F4FFF350F45C16E2010EDB50EA6A280FA1  
 :100C1000E96E040EEA22EF50E66E76C0E9FF77C077  
 :100C2000EAFF762B000E7723E552E750EF6E010EB8  
 :100C3000DB2AE2D7000ED8807955000E7A5528E2DB  
 :100C400065C0E9FF66C0EAFFEE52080EEF6E65C0B0  
 :100C5000E9FF66C0EAFF020EE926000EEA22280E2E  
 :100C6000EE6E040EED6E63C0E9FF64C0EAFFEF5064  
 :100C7000400B07E165C0E9FF66C0EAFFC80EEF6EF2  
 :100C800006D065C0E9FF66C0EAFF880EEF6E25D08A  
 :100C900065C0E9FF66C0EAFFEE52080EEF6E65C060  
 :100CA000E9FF66C0EAFF020EE926000EEA22200EE6  
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here's my python script for PyUSB (also uses PyQt for the GUI):

 ###########################################  
 # PyUSB and PIC18F2550 demo  (first revision)    #  
 # Julius 'yus' Constante    Nov. 21, 2009         #  
 ###########################################  
   
 import sys, usb  
 from PyQt4.QtCore import *  
 from PyQt4.QtGui import *  
   
 class UsbPic:  
   def __init__(self, vendor_id, product_id):  
     busses = usb.busses() # enumerate busses  
     self.handle = None  
     for bus in busses:  
       devices = bus.devices  
       for dev in devices:  
         if dev.idVendor==vendor_id and dev.idProduct==product_id: # device matches  
           self.dev = dev  
           self.conf = self.dev.configurations[0]  
           self.intf = self.conf.interfaces[0][0]  
           self.endpoints = []  
           for endpoint in self.intf.endpoints:  
             self.endpoints.append(endpoint)  
           return  
       
   def open(self):  
     if self.handle:  
       self.handle = None  
     try:  
       self.handle = self.dev.open()  
       self.handle.detachKernelDriver(0)  
       self.handle.detachKernelDriver(1)  
       self.handle.setConfiguration(self.conf)  
       self.handle.claimInterface(self.intf)  
       self.handle.setAltInterface(self.intf)  
       return True  
     except:  
       return False  
   
   def write(self, ep, buff, timeout = 100):  
     try:  
       return self.handle.interruptWrite(ep, buff, timeout) #return bytes written  
     except:  
       return 0  
   def read(self, ep, size, timeout = 100):  
     try:  
       return self.handle.interruptRead(ep, size, timeout) # return data read  
     except:  
       return []  
   def getDeviceName(self):  
     return self.handle.getString(2, 40)  
       
 class SimpleForm(QDialog):  
   def __init__(self, parent = None):  
     super(SimpleForm, self).__init__(parent)  
     self.setWindowTitle('PIC18F and PyUSB')  
     self.setMinimumSize(270, 180)  
     # create widgets/controls  
     self.connect_btn = QPushButton('Connect')  
     self.toggle1_btn = QPushButton('Toggle LED1')  
     self.toggle2_btn = QPushButton('Toggle LED2')  
     self.pot_position = QDial()  
     self.pot_label = QLabel('Potentiometer Position')  
     self.status_label = QLabel('   press "Connect" button')  
     self.update_timer = QTimer()  
     # form layout and widgets location  
     layout = QGridLayout()  
     layout.addWidget(self.connect_btn, 9, 0, 2, 1)  
     layout.addWidget(self.pot_position, 0, 0, 8, 7)  
     layout.addWidget(self.pot_label, 8, 0, 1, 7)  
     layout.addWidget(self.toggle1_btn, 4, 7)  
     layout.addWidget(self.toggle2_btn, 5, 7)  
     layout.addWidget(self.status_label, 9, 1, 2, 7)  
     self.setLayout(layout)  
     # widgets initial condition  
     self.toggle1_btn.setEnabled(False)  
     self.toggle2_btn.setEnabled(False)  
     self.pot_position.setEnabled(False) #read only  
     self.pot_position.setNotchesVisible(True)  
     self.pot_position.setRange(0, 255) # for PIC 8-bit ADC value  
     self.pot_label.setAlignment(Qt.AlignHCenter)  
     # signals  
     self.connect(self.connect_btn, SIGNAL("clicked()"), self.DeviceConnect)  
     self.connect(self.toggle1_btn, SIGNAL("clicked()"), self.toggleLED1)  
     self.connect(self.toggle2_btn, SIGNAL("clicked()"), self.toggleLED2)  
     self.connect(self.update_timer, SIGNAL("timeout()"), self.updatePotPosition)  
     
   def DeviceConnect(self):  
     self.device = UsbPic(0x04d8, 0x0204) # Microchip Vendor ID and Product ID  
     if self.device.open():  
       self.toggle1_btn.setEnabled(True)  
       self.toggle2_btn.setEnabled(True)  
       self.update_timer.start(200) # update every 200ms  
       self.status_label.setText('Connected to:\n %s' %self.device.getDeviceName())  
     else:  
       self.toggle1_btn.setEnabled(False)  
       self.toggle2_btn.setEnabled(False)  
       self.update_timer.stop()  
       self.status_label.setText('Warning:\n No Device Found!')  
     
   def toggleLED1(self):  
     self.device.write(1, [0x80], 1000)  
       
   def toggleLED2(self):  
     self.device.write(1, [0x82], 1000)  
     
   def updatePotPosition(self):  
     self.device.write(1, [0x81])  
     byteread = self.device.read(0x81, 64)  
     if len(byteread)>1:  
       self.pot_position.setValue(byteread[1])  
   
 if __name__ == '__main__':  
   app = QApplication(sys.argv)  
   form = SimpleForm()  
   form.show()  
   sys.exit(app.exec_())  
   

And finally, the actual circuit in action:


additional useful links:
Microchip USB Framework for PIC18, PIC24 & PIC32
LibUSB Win32