2
私は基本的なハンドシェイクをしようとしています。以下は、C8051F120のSMBus（システム管理バス）のISRです。私はそれにI2Cデバイスを実装しようとしています（興味がある人はads1115 7addr 0x48）。これは、主にF120のシリコンラボによって与えられた例であることに注意してください。SMBus（I2C）が意図した余分なACKを送る
void SMBUS_ISR (void) interrupt 7
{
bit FAIL = 0; // Used by the ISR to flag failed
// transfers
static unsigned char sent_byte_counter;
static unsigned char rec_byte_counter;
// Status code for the SMBus (SMB0STA register)
switch (SMB0STA)
{
// Master Transmitter/Receiver: START condition transmitted.
// Load SMB0DAT with slave device address.
case SMB_START: //0x08
// Master Transmitter/Receiver: repeated START condition transmitted.
// Load SMB0DAT with slave device address
case SMB_RP_START: //0x10
SMB0DAT = TARGET; // Load address of the slave.
SMB0DAT &= 0xFE; // Clear the LSB of the address for the
// R/W bit
SMB0DAT |= SMB_RW; // Load R/W bit
STA = 0; // Manually clear STA bit
rec_byte_counter = 1; // Reset the counter
sent_byte_counter = 1; // Reset the counter
break;
// Master Transmitter: Slave address + WRITE transmitted. ACK received.
// For a READ: N/A
//
// For a WRITE: Send the first data byte to the slave.
case SMB_MTADDACK: //0x18
SMB0DAT = SMB_DATA_OUT[sent_byte_counter-1];
sent_byte_counter++;
break;
// Master Transmitter: Slave address + WRITE transmitted. NACK received.
// Restart the transfer.
case SMB_MTADDNACK: //0x20
STA = 1; // Restart transfer
break;
// Master Transmitter: Data byte transmitted. ACK received.
// For a READ: N/A
//
// For a WRITE: Send all data. After the last data byte, send the stop
// bit.
case SMB_MTDBACK: //0x28
if (sent_byte_counter <= NUM_BYTES_WR)
{
// send data byte
SMB0DAT = SMB_DATA_OUT[sent_byte_counter-1];
sent_byte_counter++;
}
else
{
STO = 1; // Set STO to terminate transfer
SMB_BUSY = 0; // And free SMBus interface
}
break;
// Master Transmitter: Data byte transmitted. NACK received.
// Restart the transfer.
case SMB_MTDBNACK: //0x30
STA = 1; // Restart transfer
break;
// Master Receiver: Slave address + READ transmitted. ACK received.
// For a READ: check if this is a one-byte transfer. if so, set the
// NACK after the data byte is received to end the transfer. if not,
// set the ACK and receive the other data bytes.
//
// For a WRITE: N/A
case SMB_MRADDACK: //0x40
if (rec_byte_counter == NUM_BYTES_RD)
{
AA = 0; // Only one byte in this transfer,
// send NACK after byte is received
}
else
{
AA = 1; // More than one byte in this transfer,
// send ACK after byte is received
}
break;
// Master Receiver: Slave address + READ transmitted. NACK received.
// Restart the transfer.
case SMB_MRADDNACK: //0x48
STA = 1; // Restart transfer
break;
// Master Receiver: Data byte received. ACK transmitted.
// For a READ: receive each byte from the slave. if this is the last
// byte, send a NACK and set the STOP bit.
//
// For a WRITE: N/A
case SMB_MRDBACK: //0x50
if (rec_byte_counter < NUM_BYTES_RD)
{
SMB_DATA_IN[rec_byte_counter-1] = SMB0DAT; // Store received byte
AA = 1; // Send ACK to indicate byte received
rec_byte_counter++; // Increment the byte counter
}
else
{
AA = 0; // Send NACK to indicate last byte
// of this transfer
}
break;
// Master Receiver: Data byte received. NACK transmitted.
// For a READ: Read operation has completed. Read data register and
// send STOP.
//
// For a WRITE: N/A
case SMB_MRDBNACK: //0x58
SMB_DATA_IN[rec_byte_counter-1] = SMB0DAT; // Store received byte
STO = 1;
SMB_BUSY = 0;
AA = 1; // Set AA for next transfer
break;
// Master Transmitter: Arbitration lost.
case SMB_MTARBLOST: //0x38
FAIL = 1; // Indicate failed transfer
// and handle at end of ISR
break;
// All other status codes invalid. Reset communication.
default:
FAIL = 1;
break;
}
if (FAIL) // If the transfer failed,
{
SMB0CN &= ~0x40; // Reset communication
SMB0CN |= 0x40;
STA = 0;
STO = 0;
AA = 0;
SMB_BUSY = 0; // Free SMBus
FAIL = 0;
}
SI = 0; // Clear interrupt flag
}
//-----------------------------------------------------------------------------
// Support Functions
//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
// SMB_Write
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters : None
//
// Writes a single byte to the slave with address specified by the <TARGET>
// variable.
// Calling sequence:
// 1) Write target slave address to the <TARGET> variable
// 2) Write outgoing data to the <SMB_DATA_OUT> array
// 3) Call SMB_Write()
//
void SMB_Write (void)
{
char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page
SFRPAGE = SMB0_PAGE;
while (SMB_BUSY); // Wait for SMBus to be free.
SMB_BUSY = 1; // Claim SMBus (set to busy)
SMB_RW = 0; // Mark this transfer as a WRITE
STA = 1; // Start transfer
SFRPAGE = SFRPAGE_SAVE; // Restore SFR page detector
}
//-----------------------------------------------------------------------------
// SMB_Read
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters : None
//
// Reads a single byte from the slave with address specified by the <TARGET>
// variable.
// Calling sequence:
// 1) Write target slave address to the <TARGET> variable
// 2) Call SMB_Write()
// 3) Read input data from <SMB_DATA_IN> array
//
void SMB_Read (void)
{
char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page
SFRPAGE = SMB0_PAGE;
while (SMB_BUSY); // Wait for bus to be free.
SMB_BUSY = 1; // Claim SMBus (set to busy)
SMB_RW = 1; // Mark this transfer as a READ
STA = 1; // Start transfer
while (SMB_BUSY); // Wait for transfer to complete
SFRPAGE = SFRPAGE_SAVE; // Restore SFR page detector
}
メインは連続して次のことを行います。3バイトを送信します。最初のバイトはデバイスレジスタポインタです。次に、同じレジスタを読み込みます（ポインタはすでに設定されているため）。それはこれをします。
while (1)
{
TARGET = SLAVE_ADDR; // Target the Slave for next SMBus
// transfer
SMB_DATA_OUT[0] = 0x01; // Device register
SMB_DATA_OUT[1] = 0x0A; // Register MSByte
SMB_DATA_OUT[2] = 0x03; // Register LSbyte
SMB_Write(); // Initiate SMBus write
// SMBus Read Sequence
TARGET = SLAVE_ADDR; // Target the Slave for next SMBus
// transfer
SMB_Read();
}
そしてここtrace capture of transferです：
マスターが余分なACKを送信して受け取るように私には見えます。だから私の主な焦点は、ケースにされています：
SMB_MRADDACK：// 0x40の
SMB_MRADDNACK：// 0x48
SMB_MRDBACK：// 0x50を
私の主な焦点は、より多くのようにSMB_MRADDNACKです：// 0x48とそれがISR呼び出しの間のif文を通過する回数。私はちょっとしたトラブルを抱えて、正確な失敗点の周りに頭を包んでいます。では、この余分なACKはどこから来ますか？月曜日の午後、ここまでに私がそれを理解しなければ、私はここを振り返ります。
ボーナスに関する質問：何らかの種類の埋め込みスタック交換がありますか？コミュニティで私の目立つものは見当たりませんでした。
ボーナス回答：Cygnal/SiLabsフォーラム（http://community.silabs.com/）に行ったことがありますか？それはSOフォーマットではありませんが、これは非常に有能な人たちによってアクティブになっています。 –