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Optimize read/write cycle functions

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If multiple read or write cycles are done in sequence, we'll no longer
needlessly update the data direction registers (which is a slow SPI
transaction). We can also skip updating the pullups on the AVR if
multiple read cycles occur in sequence.
This commit is contained in:
Doug Brown 2020-11-25 22:08:02 -08:00 committed by Doug Brown
parent 2943b80c42
commit 9521494971
1 changed files with 75 additions and 40 deletions
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37
hal/at90usb646/parallel_bus.c
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@ -74,6 +74,8 @@ static const GPIOPin flashWEPin = {GPIOB, FLASH_WE_PIN};
static const GPIOPin flashOEPin = {GPIOB, FLASH_OE_PIN};
/// The /CS pin for the flash chip
static const GPIOPin flashCSPin = {GPIOB, FLASH_CS_PIN};
/// Whether or not data pins are outputs
static bool dataIsOutput;
/** Initializes the 32-bit data/21-bit address parallel bus.
*
@ -100,6 +102,7 @@ void ParallelBus_Init(void)
// Set all data lines to pulled-up inputs
ParallelBus_SetDataDir(0);
ParallelBus_SetDataPullups(0xFFFFFFFF);
dataIsOutput = false;
// Note: During normal operation of read/write cycles, the pullups in the
// MCP23S17 will remember they are enabled, so we can do an optimization
// when using ParallelBus_ReadCycle/WriteCycle and assume they are already
@ -225,6 +228,10 @@ void ParallelBus_SetAddressDir(uint32_t outputs)
/** Sets which pins on the 32-bit data bus should be outputs
*
* @param outputs Mask of pins that should be outputs. 1 = output, 0 = input
*
* Typically all pins would be set as inputs or outputs, and it's automatically
* handled by the read/write cycle functions. This function exists mainly for
* test purposes.
*/
void ParallelBus_SetDataDir(uint32_t outputs)
{
@ -241,6 +248,17 @@ void ParallelBus_SetDataDir(uint32_t outputs)
// D0-D15 are part of the MCP23S17
MCP23S17_SetDDR(&mcp23s17, u.dataShorts[1]);
// If none of the pins are outputs, ensure dataIsOutput is false
if (outputs == 0)
{
dataIsOutput = false;
}
// If all of the pins are outputs, ensure dataIsOutput is true
else if (outputs == 0xFFFFFFFFUL)
{
dataIsOutput = true;
}
}
/** Sets the direction of the CS pin
@ -435,7 +453,7 @@ bool ParallelBus_ReadWE(void)
/** Performs a write cycle on the parallel bus.
*
* @param address The address to read from
* @param address The address to write to
* @param data The 32-bit data to write to the bus
*
* Because this function is used a lot during programming, it is super
@ -462,6 +480,9 @@ void ParallelBus_WriteCycle(uint32_t address, uint32_t data)
u.bytes[2] = (u.bytes[2] & 0x03) | ((u.bytes[2] & 0x1C) << 2) | (PORTD & 0x8C);
PORTD = u.bytes[2];
// If the data port is not already set as outputs, set it to be outputs now
if (!dataIsOutput)
{
// Set data as outputs. Bypass the SPI/GPIO drivers for this for efficiency.
DDRE = 0xFF;
DDRF = 0xFF;
@ -471,6 +492,8 @@ void ParallelBus_WriteCycle(uint32_t address, uint32_t data)
SPITransferNoRead(0);
SPITransferNoRead(0);
DeassertControl(MCP_CS_PIN);
dataIsOutput = true;
}
// Set data. Bypass the SPI/GPIO drivers again...
u.word = data;
@ -511,6 +534,9 @@ uint32_t ParallelBus_ReadCycle(uint32_t address)
// We should currently be in a state of "CS is asserted, OE/WE not asserted".
// As an optimization, operate under that assumption.
// If the data pins are set as outputs, change them to inputs
if (dataIsOutput)
{
// Set data as inputs. Bypass the SPI/GPIO drivers for this for efficiency.
DDRE = 0;
DDRF = 0;
@ -528,6 +554,9 @@ uint32_t ParallelBus_ReadCycle(uint32_t address)
PORTE = 0xFF;
PORTF = 0xFF;
dataIsOutput = false;
}
// Assert OE so we start reading from the chip. Safe to do now that
// the data pins have been set as inputs.
AssertControl(FLASH_OE_PIN);
@ -584,6 +613,9 @@ void ParallelBus_Read(uint32_t startAddress, uint32_t *buf, uint16_t len)
uint8_t bytes[4];
} u;
// If the data pins are set as outputs, change them to inputs
if (dataIsOutput)
{
// Set data as inputs. Bypass the SPI/GPIO drivers for this for efficiency.
DDRE = 0;
DDRF = 0;
@ -601,6 +633,9 @@ void ParallelBus_Read(uint32_t startAddress, uint32_t *buf, uint16_t len)
PORTE = 0xFF;
PORTF = 0xFF;
dataIsOutput = false;
}
// Assert OE, now the chip will start spitting out data.
AssertControl(FLASH_OE_PIN);