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Merged
merged 3 commits into from
May 26, 2022
Merged

Implement hardware flow control on SAMD busio.UART #6434

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fb3077c
Implement UART hardware flow control on SAMD chips
stonehippo May 25, 2022
99b23b9
fix comment typo and mention datasheet
stonehippo May 26, 2022
8539d65
flip CTS and RTS pinmux to match RX and TX
stonehippo May 26, 2022
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62 changes: 56 additions & 6 deletions ports/atmel-samd/common-hal/busio/UART.c
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Original file line number Diff line number Diff line change
Expand Up @@ -71,19 +71,26 @@ void common_hal_busio_uart_construct(busio_uart_obj_t *self,
uint8_t rx_pad = 255; // Unset pad
uint32_t tx_pinmux = 0;
uint8_t tx_pad = 255; // Unset pad
uint32_t rts_pinmux = 0;
uint32_t cts_pinmux = 0;

// Set state so the object is deinited to start.
self->rx_pin = NO_PIN;
self->tx_pin = NO_PIN;
self->rts_pin = NO_PIN;
self->cts_pin = NO_PIN;

if ((rts != NULL) || (cts != NULL) || (rs485_dir != NULL) || (rs485_invert)) {
if ((rs485_dir != NULL) || (rs485_invert)) {
mp_raise_NotImplementedError(translate("RS485"));
}

mp_arg_validate_int_max(bits, 8, MP_QSTR_bits);

bool have_tx = tx != NULL;
bool have_rx = rx != NULL;
bool have_rts = rts != NULL;
bool have_cts = cts != NULL;

if (!have_tx && !have_rx) {
mp_raise_ValueError(translate("tx and rx cannot both be None"));
}
Expand Down Expand Up @@ -122,6 +129,9 @@ void common_hal_busio_uart_construct(busio_uart_obj_t *self,
#endif
tx_pinmux = PINMUX(tx->number, (i == 0) ? MUX_C : MUX_D);
tx_pad = tx->sercom[i].pad;
if (have_rts) {
rts_pinmux = PINMUX(rts->number, (i == 0) ? MUX_C : MUX_D);
}
if (rx == NULL) {
sercom = potential_sercom;
break;
Expand All @@ -134,6 +144,9 @@ void common_hal_busio_uart_construct(busio_uart_obj_t *self,
rx->sercom[j].pad != tx_pad) {
rx_pinmux = PINMUX(rx->number, (j == 0) ? MUX_C : MUX_D);
rx_pad = rx->sercom[j].pad;
if (have_cts) {
cts_pinmux = PINMUX(cts->number, (j == 0) ? MUX_C : MUX_D);
}
sercom = sercom_insts[rx->sercom[j].index];
sercom_index = rx->sercom[j].index;
break;
Expand Down Expand Up @@ -190,24 +203,35 @@ void common_hal_busio_uart_construct(busio_uart_obj_t *self,
// which don't necessarily match what we need. After calling it, set the values
// specific to this instantiation of UART.

// Set pads computed for this SERCOM.
// Set pads computed for this SERCOM. Refer to the datasheet for details on pads.
// TXPO:
// 0x0: TX pad 0; no RTS/CTS
// 0x1: TX pad 2; no RTS/CTS
// 0x2: TX pad 0; RTS: pad 2, CTS: pad 3 (not used by us right now)
// So divide by 2 to map pad to value.
// 0x1: reserved
// 0x2: TX pad 0; RTS: pad 2, CTS: pad 3
// 0x3: TX pad 0; RTS: pad 2; no CTS
// RXPO:
// 0x0: RX pad 0
// 0x1: RX pad 1
// 0x2: RX pad 2
// 0x3: RX pad 3

// Default to TXPO with no RTS/CTS
uint8_t computed_txpo = 0;
// If we have both CTS (with or without RTS), use second pinout
if (have_cts) {
computed_txpo = 2;
}
// If we have RTS only, use the third pinout
if (have_rts && !have_cts) {
computed_txpo = 3;
}

// Doing a group mask and set of the registers saves 60 bytes over setting the bitfields individually.

sercom->USART.CTRLA.reg &= ~(SERCOM_USART_CTRLA_TXPO_Msk |
SERCOM_USART_CTRLA_RXPO_Msk |
SERCOM_USART_CTRLA_FORM_Msk);
sercom->USART.CTRLA.reg |= SERCOM_USART_CTRLA_TXPO(tx_pad / 2) |
sercom->USART.CTRLA.reg |= SERCOM_USART_CTRLA_TXPO(computed_txpo) |
SERCOM_USART_CTRLA_RXPO(rx_pad) |
(parity == BUSIO_UART_PARITY_NONE ? 0 : SERCOM_USART_CTRLA_FORM(1));

Expand Down Expand Up @@ -257,6 +281,26 @@ void common_hal_busio_uart_construct(busio_uart_obj_t *self,
self->rx_pin = NO_PIN;
}

if (have_rts) {
gpio_set_pin_direction(rts->number, GPIO_DIRECTION_OUT);
gpio_set_pin_pull_mode(rts->number, GPIO_PULL_OFF);
gpio_set_pin_function(rts->number, rts_pinmux);
self->rts_pin = rts->number;
claim_pin(rts);
} else {
self->rts_pin = NO_PIN;
}

if (have_cts) {
gpio_set_pin_direction(cts->number, GPIO_DIRECTION_IN);
gpio_set_pin_pull_mode(cts->number, GPIO_PULL_OFF);
gpio_set_pin_function(cts->number, cts_pinmux);
self->cts_pin = cts->number;
claim_pin(cts);
} else {
self->cts_pin = NO_PIN;
}

usart_async_enable(usart_desc_p);
}

Expand All @@ -270,6 +314,8 @@ void common_hal_busio_uart_never_reset(busio_uart_obj_t *self) {
never_reset_sercom(hw);
never_reset_pin_number(self->rx_pin);
never_reset_pin_number(self->tx_pin);
never_reset_pin_number(self->rts_pin);
never_reset_pin_number(self->cts_pin);
}
}
return;
Expand All @@ -289,8 +335,12 @@ void common_hal_busio_uart_deinit(busio_uart_obj_t *self) {
usart_async_deinit(usart_desc_p);
reset_pin_number(self->rx_pin);
reset_pin_number(self->tx_pin);
reset_pin_number(self->rts_pin);
reset_pin_number(self->cts_pin);
self->rx_pin = NO_PIN;
self->tx_pin = NO_PIN;
self->rts_pin = NO_PIN;
self->cts_pin = NO_PIN;
}

// Read characters.
Expand Down
2 changes: 2 additions & 0 deletions ports/atmel-samd/common-hal/busio/UART.h
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,8 @@ typedef struct {
struct usart_async_descriptor usart_desc;
uint8_t rx_pin;
uint8_t tx_pin;
int8_t rts_pin;
int8_t cts_pin;
uint8_t character_bits;
bool rx_error;
uint32_t baudrate;
Expand Down