CEC (consumer electronic control) C library using the STM32F101xx
Contents
1. Avr UM0685 Yy User manual CEC consumer electronic control C library using the STM32F101xx STM32F102xx and STM32F103xx microcontrollers Introduction This user manual describes the CEC library using the STM32F10xxx microcontroller family Consumer electronic control CEC is a feature of the HDMI interface 1 3 standard high definition multimedia interface which is used to transmit audio video data for multimedia consumer products such as HDTV DVDs satellite receivers etc This library contains the following functions for a basic CEC communication Send Receive CEC Start bit Send Receive CEC ACK bit logical 0 Send Receive CEC data bit Send Receive CEC data byte Send Receive CEC data frame Note that the provided CEC library supports only messages addressed to a single device and not broadcast messages please refer to HDMI CEC specification March 2009 Rev 1 1 23 www st com Contents UM0685 Contents 1 CEC library description 0 000 e eee eee eee 6 2 CEC communication 4 6656 cc p rtr rr RR ee eee Dee EE 7 2 1 CEO frame st kine send Si eee eee Ten Sead 7 2 2 Hardware Considerations s sese eh RR ca nese ee ne 7 3 GEC library functions uud kw yox Rr hri Ra EROR FORERO on 8 3 1 CEC low level functions 0 0 ccc eee nee 8 3 1 1 CEC TAIC TUNCHON sos cde eede coe daw he eda ske REE ERE ad 8 3 1 2 CEC_NVIC_Configuration function llle2. 9 3 1 3 CEC Waiti00us function 0 0 cece ee 9 3 1 4 CEC_TimingDelay_Decrement function llle 9 3 2 CEC medium level functions llle 10 3 2 1 CEC SendStartBit function 0 cee ee ee 10 3 2 2 CEC_ReceiveStartBit function 0 0 0 cee 10 3 2 3 CEC SendAckBit function 0 0 00 ikam renner ken 11 3 2 4 CEC_ReceiveAckBit fUNCHION 1 0 cee 11 3 2 5 CEC SendDataBit function 0 0 0 12 3 2 6 CEC ReceiveDataBit function eee eee 12 3 2 7 CEC SendByte function tedir dekin Enui 13 3 2 8 CEC_ReceiveByte function 1 eee 14 3 3 CEC high level functions 2 2ch 22 00 Ch been acti ee teense we Samo 14 3 3 1 CEC_SendFrame function 0 0 eee eee 14 3 3 2 CEC_ReceiveFrame function 0 0 0 ee eee 15 4 How to run the CEC demo 200 0c cece eee eee 18 4 1 Example of hardware connections between the three evaluation boards 0 0 0 tees 18 4 2 CEC demo guidelines lt d c2 6sheeex Wee RETE ES RETE RT CY EE PS 18 4 3 CEC send receive information display on the LCD 19 4 4 Send subscreen information llle 19 4 5 Receive subscreen information 000 cece eee eee ees 20 5 CONCIUSION EE NN 21 2 23 ky UM0685 Contents 6 REVISION history saaavaasasee nen je saldo C CDI CR dere 22 ky 3 23 List of tables UM0685 List of tables Tabl
3. 0x00010000 define FrameSendToMeMask 0x00020000 define InitiatorAddressMask 0x000000FF Example e Inthe stm32f10x it c file define MyDeviceAddress 0x6 My device address u8 ReceiveBuffer 10 u8 ReceivedFrame 0 u32 ReceiveFrameInfos 0 Send the CEC frame void EXTIO IRQHandler void if EXTI GetITStatus EXTI Line0 RESET Receive the CEC frame with my CEC address ReceiveFrameInfos CEC _ReceiveFrame ReceiveBuffer MyDeviceAddress Set ReceivedFrame software flag to say that a frame was detected on the bus ReceivedFrame 1 Clear EXTI line 0 pending bit EXTI ClearITPendingBit EXTI Line0 e Inthe main c file include lt stdio h gt Private variables SSS Sei ae ee ad nen nn extern u8 ReceiveBuffer 10 extern u8 ReceivedFrame extern u32 ReceiveFrameInfos u8 NbOfReceivedBytes 0 If a frame has been received if ReceivedFrame Check if the frame has been received correctly if ReceiveFrameInfos amp ReceiveFrameStatusMask Check if the frame has been send to me if ReceiveFrameInfos amp FrameSendToMeMask q CEC library functions UM0685 Glow the green LED GlowGreenLED Get the number of received bytes NbOfReceivedBytes u8 ReceiveFrameInfos gt gt 8 Get the initiator address InitiatorAddress u8 ReceiveFrame
4. 15 CEC ReceiveFrame function Function name CEC ReceiveFrame Prototype u32 CEC ReceiveFrame u8 Message u8 FollLogAdd Behavior description Receives a CEC frame Message a pointer to the receive buffer l t t ER Ae FollLogAdd the device address that will receive the frame from 0 to 15 Output parameter None Return parameter a u32 integer that contains some receive information see below Required preconditions Called by the EXTI interrupt routine The contents of the u32 integer containing the CEC receive frame information returned by CEC ReceiveFrame function are 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 always read as 0 FSTM RFS 15 14 18 12 11 10 9 8 7 6 5 4 3 2 1 0 NbRB 15 8 InitADD 7 0 Bits 31 18 always read as 0 Bit 17 FSTM Frame sent to me 0 If the received frame does not have the same destination address 1 If the received frame has the same destination address Bit 16 RFS Receive frame status 0 The frame was not received correctly 1 The frame was received correctly Bits 15 8 NbRB Number of received bytes This field contains the number of received data blocks 4 15 23 CEC library functions UM0685 16 23 Bits 7 0 InitADD Initiator address This field contains the frame sender address The FSTM RFS and Initiator address masks are provided in the stm32f10x cec h file to check their status define ReceiveFrameStatusMask
5. GPIO that generates the EXTI interrupt and the NVIC IRQ channel You also have to call the CEC ReceiveFrame function in the appropriate EXTI interrupt routine 4 3 CEC send receive information display on the LCD The LCD screen is divided into two parts asubscreen that shows the CEC receive information e asubscreen that shows the CEC send information After reset each board displays the screen shown in Figure 6 Figure 6 LCD screenshot after reset Subscreen showing the receive information Subscreen showing the send information ai15936 4 4 Send subscreen information Figure 7 shows that the frame was received without error by the device with address Ox1 The receiver has acknowledged the frame 0x25 0x36 0x79 0xDF 0xA1 0xBD OxEC OxAB OxFD 0x58 Figure 7 LCD screenshot of a successful send transaction The send transaction Send to 01 The destination i i address 01 to the device with Send St atus S d address 0x01 was successful DELE EPER Data transmitted BEMEC AB FD 58 to the device with address 01 ai15937 19 23 How to run the CEC demo UM0685 4 5 20 23 In Figure 8 the frame OxAA 0x55 0x7E was not sent to the intended destination address 0x3 The frame is not acknowledged by the receiver Figure 8 LCD screen shot of a failed send transaction Send to 03 Send Status Fail Data AA 55 7E Receive subscreen information Figure 9 shows that the device h
6. boards 3 3 v 27 kQ CEC bus PAO PAO PAO STM3210B EVAL STM3210B EVAL STM3210B EVAL CEC device with CEC device with CEC device with address Ox1 address 0x2 address Ox3 Vss Vss Vss ai15935 CEC demo guidelines There are three folders in the CEC_Demo folder 1rst CEC Device 2nd_CEC_Device and 3rd_CEC_Device Each folder contains the project of a device that should be compiled and loaded into one board If only two boards are available compile and load any pair 1st Device 2nd Device 1st Device 3rd Device or 2nd Device 3rd Device to the first board and the second board respectively Run the demo on each board and the LCD display shown in Figure 6 will appear Begin the send receive transactions by pressing the key button on any board Example if you are pressing the key button on the board with the address Ox1 1st Device this board will send a frame to the board with the address 0x2 2nd Device The next time you press on the key button another frame will be sent to the board with the address 0x3 8rd Device ky UM0685 How to run the CEC demo For more details refer to sections 4 3 and section 4 4 If you are using another type of board you can show the send receive frame on the toolchain live watch By default the GPIO pin used for the CEC configuration is PAO You can use another GPIO pin by modifying some configuration in the CEC library the used GPIO the
7. the CEC start bit has been received correctly 0 if the CEC start bit has not been received correctly Required preconditions None 4 UM0685 CEC library functions Figure 3 Receive start bit flowchart Rising edge No Yes wait 100 us gt ves CEC_counter PT No CEC counter gt No Falling edge 39 3 9 ms Yes wait 100 us Yes CEC counter 2 Yes CEC counter 43 4 3 ms No No No CEC counter Exit and return Success 477 AT ms Exit and return Error Yes Exit and return Error ai15933 3 2 3 CEC SendackBit function Table 8 describes the CEC_SendAckBit function Table 8 CEC SendAckBit function Function name CEC SendAckBit Prototype void CEC SendAckBit void Behavior description Sends the CEC ACK bit ACK logical 0 Input parameter None Output parameter None Return parameter None Required preconditions None 3 2 4 CEC_ReceiveAckBit function Table 9 describes the CEC_ReceiveAckBit function Table 9 CEC_ReceiveAckBit function Function name CEC_ReceiveAckBit Prototype u8 CEC_ReceiveAckBit void Behavior description Receives the CEC ACK bit Input parameter None 11 23 CEC library functions UM0685 Table 9 CEC ReceiveAckBit function continued Function name Output parameter CEC ReceiveAckBit None Return parameter a u8 integer 0
8. 3 3 V supply voltage via a 27 kQ resistor refer to Figure 2 Figure 2 CEC Hardware requirement 3 3 V 27 KQ CEC device 1 CEC device 2 CEC device n GND ai15932 7 23 CEC library functions UM0685 3 CEC library functions The CEC library provides three types of functions e Low level functions functions that initialize and configure peripherals to be ready for CEC communication e Medium level functions functions doing elementary CEC routines e High level functions functions sending receiving CEC frames 3 1 CEC low level functions 3 1 1 CEC Init function Table 2 describes the CEC Init function Table 2 CEC Init function Function name CEC Init Prototype void CEC Init void Initializes the GPIO system tick NVIC and EXTI to communicate with the Behavior description CEC protocol Input parameter None Output parameter None Return parameter None The software has to configure the different clocks and the NVIC vector Required preconditions table base before calling this function Example void NVIC_Configuration void NVIC_InitTypeDef NVIC_InitStructure ifdef VECT TAB RAM Set the Vector Table base location to 0x20000000 NVIC SetVectorTable NVIC VectTab RAM 0x0 else VECT TAB FLASH Set the Vector Table base location to 0x08000000 NVIC SetVectorTable NVIC VectTab FLASH 0x0 endif Confi
9. Infos amp InitiatorAddressMask printf Initiator Address x n InitiatorAddress printf Received data Frame InitiatorAddress for i 0 1i lt NbOfReceivedBytes i Display the received frame printf x ReceiveBuffer i else The receive was successful but I m not the concerned destination Glow the yellow LED GlowYellowLED else The receive was failed Glow the red LED GlowRedLED ReceivedFrame 0 17 23 4 How to run the CEC demo UM0685 4 4 1 4 2 18 23 How to run the CEC demo The demo provided with this user manual is intended to run on three STM3210B EVAL evaluation boards It can be run on only two boards but in this case the send to the third device is not achieved refer to Figure 8 The demo runs at 72 MHz The CPU load for the 10 byte CEC receive or send frames over 15 seconds will be of around 2 Example of hardware connections between the three evaluation boards To run the CEC demo you have to connect the three evaluation boards as shown in Figure 5 That is you have to connect the board grounds together then all the PAO pins together they constitute the CEC bus Finally you have to connect a pull up resistor 27 kQ between the CEC bus and the 3 3 V power supply The latter can be provided by any of the boards Figure 5 CEC connections between the three STM3210B EVAL
10. LCD screenshot after reset 0 0 0 0 rns 19 Figure 7 LCD screenshot of a successful send transaction 00000 cee eee eee ee 19 Figure 8 LCD screen shot of a failed send transaction 000 0c eee eee 20 Figure 9 LCD screenshot of a successful receive transaction 0000 cece eee eens 20 Figure 10 LCD screenshot of a detected frame 0 cee 20 Figure 11 LCD screenshot of a failed receive transaction 00 000 eee 20 ky 5 23 CEC library description UM0685 6 23 CEC library description The STM32F10xxx CECLib is a set of common functions for CEC communication It includes the following functions Table 1 STM32F10xxx CEC library functions Function name CEC Init Description CEC initialization CEC NVIC Configuration CEC NVIC configuration CEC_Wait100us CEC timing for send receive a CEC bit CEC_TimingDelay_Decrement CEC time base generation CEC_SendStartBit CEC send start bit CEC_ReceiveStartBit CEC receive start bit CEC_SendAckBit CEC send acknowledge bit CEC_ReceiveAckBit CEC receive acknowledge bit CEC_SendDataBit CEC send data bit CEC_ReceiveDataBit CEC_SendByte CEC receive data bit CEC send data byte CEC_ReceiveByte CEC receive data byte CEC_SendFrame CEC send data frame CEC_ReceiveFrame CEC receive data frame x UM0685 CEC communi
11. Yes wait 100 us CEC counter em Yes Exit and return Error CEC counter Yes 20 2 ms No Exit and return bit value ai15934 3 2 7 CEC SendByte function Table 12 describes the CEC SendByte function Table 12 CEC SendByte function 2 Function name Prototype CEC SendByte ErrorStatus CEC SendByte u8 byte Behavior description Sends a CEC Header or Data block Input parameter byte the CEC opcode or operand to be transmitted Output parameter None Return parameter The status of the Header Data block transmission SUCCESS CEC byte was acknowledged by the destination ERROR CEC byte wasn t acknowledged by the destination Required preconditions None 13 23 CEC library functions UM0685 3 2 8 CEC ReceiveByte function Table 13 describes the CEC ReceiveByte function Table 13 CEC ReceiveByte function Function name CEC ReceiveByte Prototype u8 CEC ReceiveByte u8 HeaderDataIndicator Behavior description Receives a CEC Header or Data block HeaderDatalndicator indicates if the byte to receive is a Header or Data block It can be HeaderBlock for the Header block reception DataBlock for the Data block reception Input parameter Output parameter None Return parameter The received byte Required preconditions None 3 3 CEC high level functions 3 3 1 CEC SendFrame functi
12. a delay in 100 ps unit nTime Output parameter None Return parameter None Required preconditions None CEC TimingDelay Decrement function Table 5 describes the CEC TimingDelay Decrement function 9 23 CEC library functions UM0685 3 2 3 2 1 3 2 2 10 23 Table 5 CEC TimingDelay Decrement function Function name Prototype CEC TimingDelay Decrement void CEC TimingDelay Decrement void Behavior description Decrements the TimingDelay variable in the SysTick interrupt Input parameter None Output parameter None Return parameter None Required preconditions None CEC medium level functions CEC SendStartBit function Table 6 describes the C1 EC SendStartBit function Table 6 CEC SendStartBit function Function name Prototype CEC SendStartBit void CEC SendStartBit void Behavior description Sends the CEC start bit Input parameter None Output parameter None Return parameter None Required preconditions None CEC ReceiveStartBit function Table 7 describes the C EC ReceiveStartBit function Table 7 CEC ReceiveStartBit function Function name Prototype Behavior description CEC ReceiveStartBit u8 CEC ReceiveStartBit void Receives the CEC start bit Return parameter Input parameter None Output parameter None a u8 integer 1 if
13. ame with addressed messages EC ReceiveFrame receive CEC frame with addressed messages Q e oe o o o o o o o oO OG A Q O O QA OY Q Y s ky 21 23 Revision history UM0685 6 22 23 Revision history Table 16 Document revision history Date 06 Mar 2009 Revision 1 Initial release Changes UM0685 Please Read Carefully Information in this document is provided solely in connection with ST products STMicroelectronics NV and its subsidiaries ST reserve the right to make changes corrections modifications or improvements to this document and the products and services described herein at any time without notice All ST products are sold pursuant to ST s terms and conditions of sale Purchasers are solely responsible for the choice selection and use of the ST products and services described herein and ST assumes no liability whatsoever relating to the choice selection or use of the ST products and services described herein No license express or implied by estoppel or otherwise to any intellectual property rights is granted under this document If any part of this document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products or services or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such third party
14. as correctly received the frame from the sender with address 0x1 The data length only data block of the received frame is OxA 10 bytes The received data are OxDF 0x12 OxD3 0x56 0x97 OxA1 OxEC 0x7B Ox4F 0x22 Figure 9 LCD screenshot of a successful receive transaction Receive Sender Address 01 Number of bytes OA Data DE 12 D3 56 97 AT ECS BNAR 22 Figure 10 shows that the device detected a frame on the bus coming from the device with address 0x2 but it did not receive it because it is not the frame destination Figure 10 LCD screenshot of a detected frame Recei ve E Sender Address 02 Number of bytes 00 Data Figure 11 shows that an error has occurred while receiving the message Figure 11 LCD screenshot of a failed receive transaction Receive Failed Sender Address 00 Number of bytes Data UM0685 Conclusion 5 Conclusion This user manual describes the STM32F10xxx CEC library which contains the basic functions to communicate with the CEC protocol e EC Init CEC initialization EC SendStartBit send CEC start bit EC ReceiveStartBit receive CEC start bit EC SendAckBit send CEC ACK bit logical 0 EC ReceiveAckBit receive CEC ACK bit EC SendDataBit send CEC data bit EC ReceiveDataBit receive CEC data bit EC SendByte send CEC Header Data block EC ReceiveByte receive CEC Header Data block EC SendFrame Send CEC fr
15. cation 2 2 1 2 2 CEC communication CEC frame The CEC bus is a single wire protocol that can connect up to 10 audiovisual devices through standard HDMI cabling The CEC transaction is made up of a start bit a 10 bit header and a sequence of n 10 bit data blocks The Header block and the Data blocks each contain an end of message EOM bit and an acknowledge ACK bit Figure 1 shows a CEC frame format Figure 1 CEC frame 10 bits 10 bits 10 bits Start bit Header block Data bock 1 Data block n Example of Header block Example of Data block Initiator address Ox6 Destination address OxD Data OxE5 Header block Headerblock ofififofi ifofif of Data block Datablook LY of of sfof sf of Data tnitiator Destination com acx ACK ai15931 A Header block is a sequence of 10 bits the 4 bit logical address of the Initiator the 4 bit logical address of the Destination the end of message EOM bit and the Acknowledge ACK bit A Data block is a sequence of 10 bits an 8 bit field that represents the opcode or the operand the end of message EOM bit and the Acknowledge ACK bit The HDMI standard defines the opcodes and the possible number of operands for each message Hardware considerations The physical connection to the HDMI network is straightforward In accordance with the CEC specification the CEC pin of the HDMI connector has to be pulled up to a
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17. e 1 STM32F10xxx CEC library functions aavava ranerne eee 6 Table 2 CBC Tnt TUNGNON s ed Stee t Let cae ncc edb eed sen eda Gus o dried kunne 8 Table 3 CEC NVIC Configuration function eee 9 Table 4 CEC Waitl100us function esri canin AE eee ren 9 Table 5 CEC TimingDelay Decrement function llle 10 Table 6 CEC_SendStartBit function llle 10 Table 7 CEC ReceiveStartBitfunction esee res 10 Table 8 CEC SendAckBitfunction aravnn vnr eee eee ees 11 Table 9 CEC ReceiveackBit function a2ravsvv eee es 11 Table 10 CEC_SendDataBit function vvvavnnnv eee eens 12 Table 11 CEC ReceiveDataBitfunction eee eee ees 12 Table 12 CEC SendBytefunction avvvvrnnnn eee eens 13 Table 13 CEC ReceiveBytefunction vravannnn eee eens 14 Table 14 CEC_SendFrame function 0 0 cc ee ee eran 14 Table 15 CEC ReceiveFrame function 00 0000 maaa a ea re 15 Table 16 Document revision history 0 000 eens 22 4 23 y UM0685 List of figures List of figures Figure 1 CEC frame 2 serae Sr e e RR ask cast EG ak ba bite dk eee 7 Figure 2 CEC Hardware requirement llle hh 7 Figure 3 Receive start bit flowchart aauvanrna rn rn rn 11 Figure 4 Receive data bit flowchart 0 0 0 cee n 13 Figure 5 CEC connections between the three STM3210B EVAL boards 55 18 Figure 6
18. gure two bits for preemption priority NVIC PriorityGroupConfig NVIC PriorityGroup 2 int main void RCC configuration RCC Configuration 8 23 UM0685 CEC library functions 3 1 2 3 1 3 3 1 4 2 NVIC configura tion NVIC Configuration CEC initializa CEC Init tion CEC NVIC Configuration function Table 3 describes the c Table 3 EC NVIC Configuration function CEC NVIC Configuration function Function name Prototype CEC NVIC Configuration void CEC NVIC Configuration void Behavior description Configures global interrupts of SystemTick and EXTI Required preconditions Input parameter None Output parameter None Return parameter None The SystemTick and EXTI global interrupt priorities used in the CEC library have to have the highest interrupt level in the application The used and reserved NVIC configurations for the CEC library are SystemTick Preemption priority 1 subpriority 1 EXTIO Preemption priority 2 subpriority 1 CEC Waiti00us function Table 4 describes the c Table 4 EC Init function CEC Wait100us function Function name Prototype Behavior description Input parameter void CEC Waiti00us vu32 nTime nTime is the number of 100 us units to be inserted Delay 100 us x CEC Waiti00us Insert
19. on Table 14 describes the CEC SendFrame function Table 14 CEC SendFrame function Function name CEC SendFrame ErrorStatus CEC SendFrame u8 InitiatorAddress u8 FollowerAddress u8 MessageLength u8 Message Prototype Behavior description Sends a CEC frame InitiatorAddress the initiator address from 0 to 15 FollowerAddress the destination address from 0 to 15 MessageLength the number of data bytes to send Message a pointer to the transmit buffer Input parameter Output parameter None The status of the CEC frame transmission Return parameter SUCCESS If the destination received the full frame correctly ERROR the destination does not receive the full frame correctly Required preconditions None Example define MyDeviceAddress 0x6 My device address define FollowerAddress OxF Follower address to send the frame u8 NumberOfTransmitAttempt 5 u8 TransmitBuffer 10 2 0xdf 0x12 0xd3 0x56 0x97 0xa1 0xec 0x7b 0x4f 0x 22 ky 14 23 UM0685 CEC library functions ErrorStatus SendStatus ERROR Send the CEC frame do SendStatus CEC SendFrame MyDeviceAddress FollowerAddress 10 TransmitBuffer waitOneSecond NumberOfTransmitAttempt while SendStatus SUCCESS NumberOfTransmitAttempt 3 3 2 CEC ReceiveFrame function Table 15 describes the CEC ReceiveFrame function Table
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21. receive ACK bit succeeded OxFF receive ACK bit failed Required preconditions None 3 2 5 CEC SendDataBit Table 10 describes the ci function Table 10 EC SendDataBit function CEC SendDataBit function Function name Prototype CEC SendDataBit void CEC SendDataBit u8 bit Behavior description Receives the CEC ACK bit ACK logical 0 Return parameter Input parameter None Output parameter None a u8 integer 0 receive ACK bit succeeded OxFF receive ACK failed Required preconditions None 3 2 6 CEC ReceiveDataBit function Table 11 describes the CEC ReceiveDataBit function Table 11 Function name Prototype CEC ReceiveDataBit function CEC ReceiveDataBit u8 CEC ReceiveDataBit void Behavior description Receives a CEC data bit Input parameter Output parameter Return parameter None None The received data bit as a u8 integer 1 if the data bit received was logical 1 0 if the data bit received was logical 0 OxFF if the data bit has not been received correctly Required preconditions None 12 23 4 UM0685 CEC library functions Receive data bit flowchart Rising edge No Yes eum es CEC counter gt 8 0 8 ms Figure 4 wait 100us CEC counter Yes Yes No CEC counter gt 4 0 4 ms Yes bit 1 Falling edge No 9t
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