Why do you need to check for incomming USB reports every ~340uS ?
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Re: Problem with DT_HID (maybe!)
Why do you need to check for incomming USB reports every ~340uS ?
DT
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Re: Problem with DT_HID (maybe!)
There is no specific timing requirement, the period is just the maximum Timer2 would allow.
I realise that I can of course just resort to checking for incoming traffic in the main loop and in this instance that works OK. However there is obviously a restriction here that it would nice to be able to solve, i.e. how do you perform a USB read triggered by an interrupt?
I suppose that in the ideal case the receipt of USB data would trigger an interrupt of its own where the data can be processed, therefore negating the need for polling (that I do not consider to be very elegant!).
Do you think this is something worth exploring? Or is it a bit of a lost cause?
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Interrupt ON USBRX
PIC's don't generate interrupts on received USB reports.
The only indication a report was received is the buffer ownership bits which are controlled by the SIE.
So at some level, those bits must be polled.
They can be polled in the ISR, and in fact they are already being polled by DT_HID. That's how it maintains the RX_READY and TX_READY flags.
But there isn't enough time there to actually handle incomming data during the ISR because it stops USB from being serviced.
Even if you set a flag and handle it in the main loop, then that flag must be polled instead and nothing is gained except for the release of the ISR.
So the only possibility for immediate response to incoming USB data is to use a Low Priority interrupt for received reports. The USB can continue being serviced by the High Priority interrupts and receive the next report while the last data is parsed and acted upon.
But again, there are no interrupts generated for received reports. So, how to start a Low Priority Interrupt when a report arrives is the real question.
Many of the Interrupt Flags are writable (some are not). You can write a 1 to the xxxIF bit and trigger an interrupt, even though the hardware associated with the flag is disabled.
If you chose a peripheral that is not being used and will not change the flag, you can borrow its flag for your own use. (INTx, IOC, A/D etc. are not good candidates)
On the 18F4550, I would guess the HLVD interrupt will probably not be used by most programs. So in this program, I've used it to generate a Low Priority interrupt when the buffer owner bits have been polled in the High Priority ISR. Then as soon as the H.P. Int finishes the L.P. Int starts. And the L.P. can be interrupted again by the H.P.
I've aliased the HLVD_INT to USBRX_INT for readability by using the DEFINE just before the INT_LISTs. USBRX_INT is then used for the Low Priority interrupt handler.
Another Handler for USB_INT was added to the HighPriority INT_LIST.
That runs the USBRX_CHECK routine at the end of the source code.
The Reset Flag option is set to NO, so the second USB_INT will still execute too.
The end goal is to call the HandleRX subroutine immediately upon arrival of a USB report from the PC.
That, it does.
I used a LAB-XUSB developement board with an 18F4550 for testing.
Code:'*************************************************************************** '* Name : USBRX_INT.PBP * '* Author : Darrel Taylor * '* Date : 8/17/2011 * '* Version : 1.0 * '* Target : 18F4550 * '* Compiler : PBP3 * '*************************************************************************** CLEAR DEFINE OSC 48 ; Internal processor frequency #CONFIG CONFIG FOSC = HSPLL_HS CONFIG PLLDIV = 5 CONFIG USBDIV = 2 CONFIG CPUDIV = OSC1_PLL2 CONFIG FCMEN = OFF, IESO = OFF, PWRT = ON, BOR = OFF CONFIG VREGEN = ON, WDT = OFF, CCP2MX = OFF, PBADEN = OFF CONFIG MCLRE = ON, STVREN = ON, LVP = OFF, XINST = OFF #ENDCONFIG DEFINE ADC_BITS 10 'Number of bits in ADCIN result ;---[Setup Interrupts]------------------------------------------------------ DEFINE USE_LOWPRIORITY 1 ; Use Low Priority Interrupts INCLUDE "DT_INTS-18.bas" ; Base Interrupt System INCLUDE "ReEnterPBP-18.bas" ; Allows re-entry to PBP from ASM interrupts INCLUDE "ReEnterPBP-18LP.bas" ; Include if using Low Pr. PBP INTS ASM #define USBRX_INT HLVD_INT ; use HLVD as false Low Priority INT ;----[High Priority Interrupts]--------------------------------------------- INT_LIST macro ; IntSource, Label, Type, ResetFlag? INT_Handler USB_INT, USBRX_CHECK, ASM, no INT_Handler USB_Handler INT_Handler TMR1_INT, _TMR1_ISR, PBP, yes endm INT_CREATE ; Creates the interrupt processor INT_ENABLE TMR1_INT ; Enable Timer 1 Interrupts ;----[Low Priority Interrupts]---------------------------------------------- INT_LIST_L macro ; IntSource, Label, Type, ResetFlag? INT_Handler USBRX_INT, USB_Receive, PBP, yes endm INT_CREATE_L ; Creates the Low Priority interrupt processor INT_ENABLE USBRX_INT ENDASM ;---[Setup USB]------------------------------------------------------------- INCLUDE "DT_HID260.pbp" DEFINE USB_VENDORID 6017 DEFINE USB_PRODUCTID 2000 DEFINE USB_VERSION 2 DEFINE USB_VENDORNAME "Darrel Taylor" DEFINE USB_PRODUCTNAME "USBRX_INT" DEFINE USB_SERIAL "001" DEFINE USB_INSIZE 64 ; IN report is PIC to PC (8,16,32,64) DEFINE USB_OUTSIZE 16 ; OUT report is PC to PIC DEFINE USB_POLLIN 10 ; Polling times in mS, MIN=1 MAX=10 DEFINE USB_POLLOUT 10 ; --- Each USB LED is optional, comment them if not used ---- DEFINE USB_LEDPOLARITY 1 ; LED ON State [0 or 1] (default = 1) DEFINE USB_PLUGGEDLED PORTD,0 ; LED indicates if USB is connected DEFINE USB_TXLED PORTD,1 ; " " data being sent to PC DEFINE USB_RXLED PORTD,2 ; " " data being received from PC ADval VAR WORD ;----[Initialize]----------------------------------------------------------- ADCON1 = %1101 ; AN0 and AN1 Analog ADCON2.7 = 1 ; Right justify A/D results T1CON = $31 ; Prescaler = 8, TMR1ON ;----[Main Program Loop]---------------------------------------------------- Main: PAUSE 200 ;--Read AN0-- ADCIN 0, ADval ARRAYWRITE USBTXBuffer,[6,0,"0 ",DEC ADval,0] GOSUB DoUSBOut ;--Read AN1-- ADCIN 1, ADval ARRAYWRITE USBTXBuffer,[6,0,"1 ",DEC ADval,0] GOSUB DoUSBOut GOTO Main ;----[USB - Handle received reports]---------------------------------------- ; This is called from a low priority interrupt whenever a report is rcvd HandleRX: SELECT CASE USBRXBuffer(0) CASE "1" : SOUND PORTC.2, [100, 50] CASE "2" : SOUND PORTC.2, [120, 50] CASE "3" : TOGGLE PORTD.3 CASE "4" : ; send string back to PC ARRAYWRITE USBTXBuffer,[5," ",STR USBRXBuffer(1)\USBBufferSizeRX-1] GOSUB DoUSBOut END SELECT PAUSE 100 RETURN ;----[Timer1 interrupt blinks an LED]-------------------------------------- TMR_DIV VAR BYTE TMR1_ISR: TMR_DIV = TMR_DIV + 1 if TMR_DIV = 12 THEN TOGGLE PORTD.3 TMR_DIV = 0 ENDIF @ INT_RETURN ;===[Generates false L.P. interrupt on USB received reports]=*===*===*===*= ASM USBRX_CHECK btfss INTCON, GIEL ; if low priority ints are available goto Check_Done btfss _Plugged ; and USB is connected goto Check_Done btfss _RX_READY ; and report has been received goto Check_Done btfsc _RX_Rcvd ; and the RX buffer is released goto Check_Done bsf USBRX_INT ; set the false interrupt flag Check_Done INT_RETURN ; USB_Receive ON_USBRX_GOSUB _HandleRX INT_RETURN ENDASM
Last edited by Darrel Taylor; - 19th August 2011 at 03:24.
DT
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Re: Problem with DT_HID (maybe!)
Hi Darrel,
I realised that there was no dedicated USB RX interupt, hence my problem, but that is a very nice little workaround.
It works perfectly in my current setup and will no doubt be useful in the future. Thanks for all the help!
Cheers
Andy
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