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uart-bridge: disable UART when writing to LCR

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Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
This commit is contained in:
Álvaro Fernández Rojas 2023-01-31 20:19:57 +01:00
parent ca81e5c242
commit 3ce41d326b
1 changed files with 161 additions and 10 deletions
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161
uart-bridge.c
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@ -3,7 +3,9 @@
* Copyright 2021 Álvaro Fernández Rojas <noltari@gmail.com>
*/
#include <hardware/clocks.h>
#include <hardware/irq.h>
#include <hardware/resets.h>
#include <hardware/structs/sio.h>
#include <hardware/uart.h>
#include <pico/multicore.h>
@ -101,6 +103,155 @@ static inline uint stopbits_usb2uart(uint8_t stop_bits)
}
}
uint32_t uart_disable_before_lcr_write(uart_inst_t *uart)
{
// Notes from PL011 reference manual:
//
// - Before writing LCR, must disable UART and wait for current TX + RX
// char to finish
//
// - There is a BUSY flag which waits for the current TX char, but this is
// OR'd with TX FIFO !FULL, so not usable when FIFOs are enabled and
// potentially nonempty
//
// - FIFOs can't be set to disabled whilst a character is in progress
// (else "FIFO integrity is not guaranteed")
//
// Combination of these means there is no general way to halt and poll for
// end of TX character, if FIFOs may be enabled. Either way, there is no
// way to poll for end of RX character.
//
// So... we're going to insert a 15 baud period delay before changing
// settings (comfortably higher than max data + start + stop + parity).
// Anything else would require API changes to permit a non-enabled UART
// state after init() where settings can be changed safely.
uint32_t cr_save = uart_get_hw(uart)->cr;
hw_clear_bits(&uart_get_hw(uart)->cr,
UART_UARTCR_UARTEN_BITS | UART_UARTCR_TXE_BITS | UART_UARTCR_RXE_BITS);
uint32_t current_ibrd = uart_get_hw(uart)->ibrd;
uint32_t current_fbrd = uart_get_hw(uart)->fbrd;
uint64_t baud_period_usec = 1u +
((uint64_t)64 * current_ibrd + current_fbrd) /
(4u * clock_get_hz(clk_peri));
busy_wait_us(15 * baud_period_usec);
return cr_save;
}
void _uart_set_fifo_enabled(uart_inst_t *uart, bool enabled) {
bool was_enabled = uart_is_enabled(uart);
uint32_t cr_save;
if (was_enabled)
cr_save = uart_disable_before_lcr_write(uart);
hw_write_masked(&uart_get_hw(uart)->lcr_h,
(bool_to_bit(enabled) << UART_UARTLCR_H_FEN_LSB),
UART_UARTLCR_H_FEN_BITS);
if (was_enabled)
uart_get_hw(uart)->cr = cr_save;
}
uint _uart_set_baudrate(uart_inst_t *uart, uint baudrate) {
invalid_params_if(UART, baudrate == 0);
uint32_t baud_rate_div = (8 * clock_get_hz(clk_peri) / baudrate);
uint32_t baud_ibrd = baud_rate_div >> 7;
uint32_t baud_fbrd;
if (baud_ibrd == 0) {
baud_ibrd = 1;
baud_fbrd = 0;
} else if (baud_ibrd >= 65535) {
baud_ibrd = 65535;
baud_fbrd = 0;
} else {
baud_fbrd = ((baud_rate_div & 0x7f) + 1) / 2;
}
// Need to cleanly disable UART before touching LCR
bool was_enabled = uart_is_enabled(uart);
uint32_t cr_save;
if (was_enabled)
cr_save = uart_disable_before_lcr_write(uart);
uart_get_hw(uart)->ibrd = baud_ibrd;
uart_get_hw(uart)->fbrd = baud_fbrd;
// PL011 needs a (dummy) LCR_H write to latch in the divisors. We don't
// want to actually change LCR_H contents here.
hw_set_bits(&uart_get_hw(uart)->lcr_h, 0);
// Re-enable using saved control register value
if (was_enabled)
uart_get_hw(uart)->cr = cr_save;
// See datasheet
return (4 * clock_get_hz(clk_peri)) / (64 * baud_ibrd + baud_fbrd);
}
void _uart_set_format(uart_inst_t *uart, uint data_bits, uint stop_bits, uart_parity_t parity) {
invalid_params_if(UART, data_bits < 5 || data_bits > 8);
invalid_params_if(UART, stop_bits != 1 && stop_bits != 2);
invalid_params_if(UART, parity != UART_PARITY_NONE && parity != UART_PARITY_EVEN && parity != UART_PARITY_ODD);
bool was_enabled = uart_is_enabled(uart);
uint32_t cr_save;
if (was_enabled)
cr_save = uart_disable_before_lcr_write(uart);
hw_write_masked(&uart_get_hw(uart)->lcr_h,
((data_bits - 5u) << UART_UARTLCR_H_WLEN_LSB) |
((stop_bits - 1u) << UART_UARTLCR_H_STP2_LSB) |
(bool_to_bit(parity != UART_PARITY_NONE) << UART_UARTLCR_H_PEN_LSB) |
(bool_to_bit(parity == UART_PARITY_EVEN) << UART_UARTLCR_H_EPS_LSB),
UART_UARTLCR_H_WLEN_BITS |
UART_UARTLCR_H_STP2_BITS |
UART_UARTLCR_H_PEN_BITS |
UART_UARTLCR_H_EPS_BITS);
if (was_enabled)
uart_get_hw(uart)->cr = cr_save;
}
static inline void uart_reset(uart_inst_t *uart) {
invalid_params_if(UART, uart != uart0 && uart != uart1);
reset_block(uart_get_index(uart) ? RESETS_RESET_UART1_BITS : RESETS_RESET_UART0_BITS);
}
static inline void uart_unreset(uart_inst_t *uart) {
invalid_params_if(UART, uart != uart0 && uart != uart1);
unreset_block_wait(uart_get_index(uart) ? RESETS_RESET_UART1_BITS : RESETS_RESET_UART0_BITS);
}
uint _uart_init(uart_inst_t *uart, uint baudrate) {
invalid_params_if(UART, uart != uart0 && uart != uart1);
if (clock_get_hz(clk_peri) == 0)
return 0;
uart_reset(uart);
uart_unreset(uart);
#if PICO_UART_ENABLE_CRLF_SUPPORT
uart_set_translate_crlf(uart, PICO_UART_DEFAULT_CRLF);
#endif
// Any LCR writes need to take place before enabling the UART
uint baud = _uart_set_baudrate(uart, baudrate);
_uart_set_format(uart, 8, 1, UART_PARITY_NONE);
// Enable FIFOs (must be before setting UARTEN, as this is an LCR access)
hw_set_bits(&uart_get_hw(uart)->lcr_h, UART_UARTLCR_H_FEN_BITS);
// Enable the UART, both TX and RX
uart_get_hw(uart)->cr = UART_UARTCR_UARTEN_BITS | UART_UARTCR_TXE_BITS | UART_UARTCR_RXE_BITS;
// Always enable DREQ signals -- no harm in this if DMA is not listening
uart_get_hw(uart)->dmacr = UART_UARTDMACR_TXDMAE_BITS | UART_UARTDMACR_RXDMAE_BITS;
return baud;
}
void update_uart_cfg(uint8_t itf)
{
const uart_id_t *ui = &UART_ID[itf];
@ -109,14 +260,14 @@ void update_uart_cfg(uint8_t itf)
mutex_enter_blocking(&ud->lc_mtx);
if (ud->usb_lc.bit_rate != ud->uart_lc.bit_rate) {
uart_set_baudrate(ui->inst, ud->usb_lc.bit_rate);
_uart_set_baudrate(ui->inst, ud->usb_lc.bit_rate);
ud->uart_lc.bit_rate = ud->usb_lc.bit_rate;
}
if ((ud->usb_lc.stop_bits != ud->uart_lc.stop_bits) ||
(ud->usb_lc.parity != ud->uart_lc.parity) ||
(ud->usb_lc.data_bits != ud->uart_lc.data_bits)) {
uart_set_format(ui->inst,
_uart_set_format(ui->inst,
databits_usb2uart(ud->usb_lc.data_bits),
stopbits_usb2uart(ud->usb_lc.stop_bits),
parity_usb2uart(ud->usb_lc.parity));
@ -284,12 +435,12 @@ void init_uart_data(uint8_t itf)
mutex_init(&ud->usb_mtx);
/* UART start */
uart_init(ui->inst, ud->usb_lc.bit_rate);
_uart_init(ui->inst, ud->usb_lc.bit_rate);
uart_set_hw_flow(ui->inst, false, false);
uart_set_format(ui->inst, databits_usb2uart(ud->usb_lc.data_bits),
_uart_set_format(ui->inst, databits_usb2uart(ud->usb_lc.data_bits),
stopbits_usb2uart(ud->usb_lc.stop_bits),
parity_usb2uart(ud->usb_lc.parity));
uart_set_fifo_enabled(ui->inst, false);
_uart_set_fifo_enabled(ui->inst, false);
/* UART RX Interrupt */
irq_set_exclusive_handler(ui->irq, ui->irq_fn);