My platform is a c8051F120 microcontroller. I would like to send (=tx) bytes via UART0 using interrupts. My design so far is the following:
#define UART0_TX_SIZE 16
char UART0_tx[UART0_TX_SIZE];
short UART0_tx_uart = 0;
short UART0_tx_main = 0;
short UART0_tx_available = 0;
void UART0_putChar(char value) {
char SAVE_SFRPAGE;
bit EA_SAVE = EA;
// potentially blocking code
while (UART0_tx_available == UART0_TX_SIZE)
;
// disable interrupts
EA = 0;
EA = 0;
if (UART0_tx_available) {
UART0_tx[UART0_tx_main] = value;
++UART0_tx_main;
if (UART0_tx_main == UART0_TX_SIZE)
UART0_tx_main = 0;
++UART0_tx_available;
} else {
SAVE_SFRPAGE = SFRPAGE;
SFRPAGE = UART0_PAGE;
SBUF0 = value;
SFRPAGE = SAVE_SFRPAGE;
}
// reenable if necessary
EA = EA_SAVE;
}
// (return void works for other interrupts)
void UART0_Interrupt() interrupt (4) {
if (RI0 == 1) {
RI0 = 0;
}
if (TI0 == 1) { // cause of interrupt: previous tx is finished
TI0 = 0; // Q: Should this clear tx interrupt flag be further down?
if (SSTA0 & 0x20) { // Errors tx collision
SSTA0 &= 0xDF;
}
if (UART0_tx_available) { // If buffer not empty
--UART0_tx_available; // Decrease array size
SBUF0 = UART0_tx[UART0_tx_uart]; //Transmit
++UART0_tx_uart; //Update counter
if (UART0_tx_uart == UART0_TX_SIZE)
UART0_tx_uart = 0;
}
}
}
I am pretty sure that the initialization regarding UART0 registers and timing via Timer2 (not part of the above code) is correct, because I am able to use the blocking function:
char putchar_Blocking(char value) {
char SFRPAGE_SAVE = SFRPAGE;
SFRPAGE = UART0_PAGE;
while (!TI0) // while TI0 == 1 wait for transmit complete
;
TI0 = 0;
SBUF0 = value;
SFRPAGE = SFRPAGE_SAVE;
return value;
}
When I want to switch to the interrupt design, of course, I also set
ES0 = 1;
Does anybody find a flaw in my design that attempts to use the interupt? Or, does anybody have sample code for this? Thank you! And a big shout-out to jszakmeister, who answered my question regarding reading the TCNT register.
