diff --git a/ports/atmel-samd/README.rst b/ports/atmel-samd/README.rst
index 1ff2a0e80b..6037c7d3b1 100644
--- a/ports/atmel-samd/README.rst
+++ b/ports/atmel-samd/README.rst
@@ -170,13 +170,7 @@ These commands should be executed from the root directory of the repository
 
 Build commands are run from the ``circuitpython/ports/atmel-samd`` directory.
 
-To build for the Arduino Zero:
-
-.. code-block:: shell
-
-    make
-
-To build for other boards you must change it by setting ``BOARD``. For example:
+To build for a given board you must specify it by setting ``BOARD``. For example:
 
 .. code-block:: shell
 
diff --git a/ports/nrf/supervisor/qspi_flash.c b/ports/nrf/supervisor/qspi_flash.c
index 048db06f20..51a9ec0329 100644
--- a/ports/nrf/supervisor/qspi_flash.c
+++ b/ports/nrf/supervisor/qspi_flash.c
@@ -40,15 +40,13 @@
 
 bool spi_flash_command(uint8_t command) {
     nrf_qspi_cinstr_conf_t cinstr_cfg = {
-        .opcode = 0,
-        .length = 0,
+        .opcode = command,
+        .length = 1,
         .io2_level = true,
         .io3_level = true,
         .wipwait = false,
         .wren = false
     };
-    cinstr_cfg.opcode = command;
-    cinstr_cfg.length = 1;
     nrfx_qspi_cinstr_xfer(&cinstr_cfg, NULL, NULL);
     return true;
 }
@@ -62,8 +60,8 @@ bool spi_flash_read_command(uint8_t command, uint8_t* response, uint32_t length)
         .wipwait = false,
         .wren = false
     };
-    nrfx_qspi_cinstr_xfer(&cinstr_cfg, NULL, response);
-    return true;
+    return nrfx_qspi_cinstr_xfer(&cinstr_cfg, NULL, response) == NRFX_SUCCESS;
+
 }
 
 bool spi_flash_write_command(uint8_t command, uint8_t* data, uint32_t length) {
@@ -75,8 +73,7 @@ bool spi_flash_write_command(uint8_t command, uint8_t* data, uint32_t length) {
         .wipwait = false,
         .wren = false // We do this manually.
     };
-    nrfx_qspi_cinstr_xfer(&cinstr_cfg, data, NULL);
-    return true;
+    return nrfx_qspi_cinstr_xfer(&cinstr_cfg, data, NULL) == NRFX_SUCCESS;
 }
 
 bool spi_flash_sector_command(uint8_t command, uint32_t address) {
@@ -91,8 +88,7 @@ bool spi_flash_write_data(uint32_t address, uint8_t* data, uint32_t length) {
 }
 
 bool spi_flash_read_data(uint32_t address, uint8_t* data, uint32_t length) {
-    nrfx_qspi_read(data, length, address);
-    return true;
+    return nrfx_qspi_read(data, length, address) == NRFX_SUCCESS;
 }
 
 void spi_flash_init(void) {
@@ -115,7 +111,7 @@ void spi_flash_init(void) {
             .dpmconfig = false
         },
         .phy_if = {
-            .sck_freq = NRF_QSPI_FREQ_32MDIV16, // Start at a slow 2mhz and speed up once we know what we're talking to.
+            .sck_freq = NRF_QSPI_FREQ_32MDIV16, // Start at a slow 2MHz and speed up once we know what we're talking to.
             .sck_delay = 10,    // min time CS must stay high before going low again. in unit of 62.5 ns
             .spi_mode = NRF_QSPI_MODE_0,
             .dpmen = false
@@ -145,14 +141,18 @@ void spi_flash_init_device(const external_flash_device* device) {
     // Switch to single output line if the device doesn't support quad programs.
     if (!device->supports_qspi_writes) {
         NRF_QSPI->IFCONFIG0 &= ~QSPI_IFCONFIG0_WRITEOC_Msk;
-        NRF_QSPI->IFCONFIG0 |= QSPI_IFCONFIG0_WRITEOC_PP;
+        NRF_QSPI->IFCONFIG0 |= QSPI_IFCONFIG0_WRITEOC_PP << QSPI_IFCONFIG0_WRITEOC_Pos;
     }
 
     // Speed up as much as we can.
-    uint8_t sckfreq = 0;
+    // Start at 16 MHz and go down.
+    // At 32 MHz GD25Q16C doesn't work reliably on Feather 52840, even though it should work up to 104 MHz.
+    // sckfreq = 0 is 32 Mhz
+    // sckfreq = 1 is 16 MHz, etc.
+    uint8_t sckfreq = 1;
     while (32000000 / (sckfreq + 1) > device->max_clock_speed_mhz * 1000000 && sckfreq < 16) {
         sckfreq += 1;
     }
     NRF_QSPI->IFCONFIG1 &= ~QSPI_IFCONFIG1_SCKFREQ_Msk;
-    NRF_QSPI->IFCONFIG1 |=  sckfreq << QSPI_IFCONFIG1_SCKDELAY_Pos;
+    NRF_QSPI->IFCONFIG1 |=  sckfreq << QSPI_IFCONFIG1_SCKFREQ_Pos;
 }
diff --git a/supervisor/shared/stack.c b/supervisor/shared/stack.c
index 71e239c0a1..311fa31b22 100755
--- a/supervisor/shared/stack.c
+++ b/supervisor/shared/stack.c
@@ -56,7 +56,7 @@ void allocate_stack(void) {
 }
 
 inline bool stack_ok(void) {
-    return *stack_alloc->ptr == STACK_CANARY_VALUE;
+    return stack_alloc == NULL || *stack_alloc->ptr == STACK_CANARY_VALUE;
 }
 
 inline void assert_heap_ok(void) {