applications: serial_lte_modem: Free RAM for Thingy boards

Release unnecessarily used RAM to allow the CMUX + PPP
usage with Thingy:91 and CMUX + PPP + modem traces with
Thingy:91 X.

CONFIG_SLM_CMUX_UART_BUFFER_SIZE only needs to be slightly
larger than CONFIG_MODEM_CMUX_WORK_BUFFER_SIZE.

Signed-off-by: Markus Lassila <[email protected]>

Author: MarkusLassila

applications/serial_lte_modem/Kconfig

@@ -59,9 +59,11 @@ config SLM_UART_RX_BUF_COUNT
 config SLM_UART_RX_BUF_SIZE
 	int "Receive buffer size for UART"
 	range 128 4096
+	default 2048 if BOARD_THINGY91_NRF9160_NS || BOARD_THINGY91X_NRF9151_NS
 	default 256
 	help
 	  Amount of received (RX), unprocessed, UART traffic that can be held by single buffer.
+	  Increase buffer space for Thingy:91 and Thingy:91 X as hardware flow control is not used.
 	  These buffers are not used when CMUX is in use.
 
 config SLM_UART_TX_BUF_SIZE
@@ -189,7 +191,7 @@ config SLM_CMUX
 config SLM_CMUX_UART_BUFFER_SIZE
 	int "UART buffer size for CMUX"
 	depends on SLM_CMUX
-	default 6000
+	default 600
 	help
 	  Size of the buffer for data received in CMUX mode.
 	  Same buffer size is used for both RX and TX.

applications/serial_lte_modem/boards/thingy91_nrf9160_ns.conf

@@ -10,6 +10,3 @@
 
 # Configuration related to external sensors.
 CONFIG_SLM_POWER_PIN=26
-
-# Increase buffer space as hardware flow control is not used with Thingy:91.
-CONFIG_SLM_UART_RX_BUF_SIZE=2048

applications/serial_lte_modem/boards/thingy91x_nrf9151_ns.conf

@@ -10,6 +10,3 @@
 
 # Configuration related to external sensors.
 CONFIG_SLM_POWER_PIN=26
-
-# Increase buffer space as hardware flow control is not used with Thingy:91 X.
-CONFIG_SLM_UART_RX_BUF_SIZE=2048

applications/serial_lte_modem/overlay-cmux.conf

@@ -17,6 +17,12 @@ CONFIG_MODEM_BACKEND_UART_ASYNC=n
 CONFIG_MODEM_BACKEND_UART_SLM=y
 CONFIG_MODEM_BACKEND_UART_SLM_TRANSMIT_TIMEOUT_MS=1000
 
+# These buffers are unused after AT#CMUX is enabled
+# so use minimal buffer size
+CONFIG_SLM_UART_RX_BUF_COUNT=2
+CONFIG_SLM_UART_RX_BUF_SIZE=128
+CONFIG_SLM_UART_TX_BUF_SIZE=128
+
 # debug options
 #CONFIG_MODEM_CMUX_LOG_LEVEL_DBG=y
 #CONFIG_MODEM_MODULES_LOG_LEVEL_DBG=y

applications/serial_lte_modem/overlay-ppp-cmux-linux.conf

@@ -11,23 +11,23 @@ CONFIG_SLM_CR_TERMINATION=y
 
 CONFIG_MODEM_CMUX_MTU=127
 CONFIG_MODEM_CMUX_WORK_BUFFER_SIZE=536
-CONFIG_SLM_CMUX_UART_BUFFER_SIZE=6000
+CONFIG_SLM_CMUX_UART_BUFFER_SIZE=600
 
 # Enable SLM UART backend
 CONFIG_MODEM_BACKEND_UART=n
 CONFIG_MODEM_BACKEND_UART_ASYNC=n
 CONFIG_MODEM_BACKEND_UART_SLM=y
 
-# For sending full 6000 bytes at 115200 baudrate
-# 6000 * 10 / 115200 = 521 ms
-CONFIG_MODEM_BACKEND_UART_SLM_TRANSMIT_TIMEOUT_MS=521
+# For sending full 600 bytes at 115200 baudrate
+# 600 * 10 / 115200 = 52.1 ms
+CONFIG_MODEM_BACKEND_UART_SLM_TRANSMIT_TIMEOUT_MS=53
 # Assume at least baudrate 115200 for UART
 # so CMUX frame can be received in 12 ms (134*10/115200)
 CONFIG_MODEM_BACKEND_UART_SLM_RECEIVE_IDLE_TIMEOUT_MS=12
 
 # These buffers are unused after AT#CMUX is enabled
 # so use minimal buffer size
-CONFIG_SLM_UART_RX_BUF_COUNT=3
+CONFIG_SLM_UART_RX_BUF_COUNT=2
 CONFIG_SLM_UART_RX_BUF_SIZE=128
 CONFIG_SLM_UART_TX_BUF_SIZE=128